[V14] mm/debug: Add tests validating architecture page table helpers
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Message ID 1581909460-19148-1-git-send-email-anshuman.khandual@arm.com
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  • [V14] mm/debug: Add tests validating architecture page table helpers
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Commit Message

Anshuman Khandual Feb. 17, 2020, 3:17 a.m. UTC
This adds tests which will validate architecture page table helpers and
other accessors in their compliance with expected generic MM semantics.
This will help various architectures in validating changes to existing
page table helpers or addition of new ones.

This test covers basic page table entry transformations including but not
limited to old, young, dirty, clean, write, write protect etc at various
level along with populating intermediate entries with next page table page
and validating them.

Test page table pages are allocated from system memory with required size
and alignments. The mapped pfns at page table levels are derived from a
real pfn representing a valid kernel text symbol. This test gets called
inside kernel_init() right after async_synchronize_full().

This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any
architecture, which is willing to subscribe this test will need to select
ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390
and ppc32 platforms where the test is known to build and run successfully.
Going forward, other architectures too can subscribe the test after fixing
any build or runtime problems with their page table helpers. Meanwhile for
better platform coverage, the test can also be enabled with CONFIG_EXPERT
even without ARCH_HAS_DEBUG_VM_PGTABLE.

Folks interested in making sure that a given platform's page table helpers
conform to expected generic MM semantics should enable the above config
which will just trigger this test during boot. Any non conformity here will
be reported as an warning which would need to be fixed. This test will help
catch any changes to the agreed upon semantics expected from generic MM and
enable platforms to accommodate it thereafter.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Mike Rapoport <rppt@linux.ibm.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Kirill A. Shutemov <kirill@shutemov.name>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: linux-snps-arc@lists.infradead.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linuxppc-dev@lists.ozlabs.org
Cc: linux-s390@vger.kernel.org
Cc: linux-riscv@lists.infradead.org
Cc: x86@kernel.org
Cc: linux-arch@vger.kernel.org
Cc: linux-kernel@vger.kernel.org

Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Tested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>	# s390
Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>	# ppc32
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
---
This adds a test validation for architecture exported page table helpers.
Patch adds basic transformation tests at various levels of the page table.

This test was originally suggested by Catalin during arm64 THP migration
RFC discussion earlier. Going forward it can include more specific tests
with respect to various generic MM functions like THP, HugeTLB etc and
platform specific tests.

https://lore.kernel.org/linux-mm/20190628102003.GA56463@arrakis.emea.arm.com/

Needs to be applied on linux V5.6-rc2

Changes in V14:

- Disabled DEBUG_VM_PGFLAGS for IA64 and ARM (32 Bit) per Andrew and Christophe
- Updated DEBUG_VM_PGFLAGS documentation wrt EXPERT and disabled platforms
- Updated RANDOM_[OR|NZ]VALUE open encodings with GENMASK() per Catalin
- Updated s390 constraint bits from 12 to 4 (S390_MASK_BITS) per Gerald
- Updated in-code documentation for RANDOM_ORVALUE per Gerald
- Updated pxx_basic_tests() to use invert functions first per Catalin
- Dropped ARCH_HAS_4LEVEL_HACK check from pud_basic_tests()
- Replaced __ARCH_HAS_[4|5]LEVEL_HACK with __PAGETABLE_[PUD|P4D]_FOLDED per Catalin
- Trimmed the CC list on the commit message per Catalin

Changes in V13: (https://patchwork.kernel.org/project/linux-mm/list/?series=237125)

- Subscribed s390 platform and updated debug-vm-pgtable/arch-support.txt per Gerald
- Dropped keyword 'extern' from debug_vm_pgtable() declaration per Christophe
- Moved debug_vm_pgtable() declarations to <linux/mmdebug.h> per Christophe
- Moved debug_vm_pgtable() call site into kernel_init() per Christophe
- Changed CONFIG_DEBUG_VM_PGTABLE rules per Christophe
- Updated commit to include new supported platforms and changed config selection

Changes in V12: (https://patchwork.kernel.org/project/linux-mm/list/?series=233905)

- Replaced __mmdrop() with mmdrop()
- Enable ARCH_HAS_DEBUG_VM_PGTABLE on X86 for non CONFIG_X86_PAE platforms as the
  test procedure interfere with pre-allocated PMDs attached to the PGD resulting
  in runtime failures with VM_BUG_ON()

Changes in V11: (https://patchwork.kernel.org/project/linux-mm/list/?series=221135)

- Rebased the patch on V5.4

Changes in V10: (https://patchwork.kernel.org/project/linux-mm/list/?series=205529)

- Always enable DEBUG_VM_PGTABLE when DEBUG_VM is enabled per Ingo
- Added tags from Ingo

Changes in V9: (https://patchwork.kernel.org/project/linux-mm/list/?series=201429)

- Changed feature support enumeration for powerpc platforms per Christophe
- Changed config wrapper for basic_[pmd|pud]_tests() to enable ARC platform
- Enabled the test on ARC platform

Changes in V8: (https://patchwork.kernel.org/project/linux-mm/list/?series=194297)

- Enabled ARCH_HAS_DEBUG_VM_PGTABLE on PPC32 platform per Christophe
- Updated feature documentation as DEBUG_VM_PGTABLE is now enabled on PPC32 platform
- Moved ARCH_HAS_DEBUG_VM_PGTABLE earlier to indent it with DEBUG_VM per Christophe
- Added an information message in debug_vm_pgtable() per Christophe
- Dropped random_vaddr boundary condition checks per Christophe and Qian
- Replaced virt_addr_valid() check with pfn_valid() check in debug_vm_pgtable()
- Slightly changed pr_fmt(fmt) information

Changes in V7: (https://patchwork.kernel.org/project/linux-mm/list/?series=193051)

- Memory allocation and free routines for mapped pages have been droped
- Mapped pfns are derived from standard kernel text symbol per Matthew
- Moved debug_vm_pgtaable() after page_alloc_init_late() per Michal and Qian 
- Updated the commit message per Michal
- Updated W=1 GCC warning problem on x86 per Qian Cai
- Addition of new alloc_contig_pages() helper has been submitted separately

Changes in V6: (https://patchwork.kernel.org/project/linux-mm/list/?series=187589)

- Moved alloc_gigantic_page_order() into mm/page_alloc.c per Michal
- Moved alloc_gigantic_page_order() within CONFIG_CONTIG_ALLOC in the test
- Folded Andrew's include/asm-generic/pgtable.h fix into the test patch 2/2

Changes in V5: (https://patchwork.kernel.org/project/linux-mm/list/?series=185991)

- Redefined and moved X86 mm_p4d_folded() into a different header per Kirill/Ingo
- Updated the config option comment per Ingo and dropped 'kernel module' reference
- Updated the commit message and dropped 'kernel module' reference
- Changed DEBUG_ARCH_PGTABLE_TEST into DEBUG_VM_PGTABLE per Ingo
- Moved config option from mm/Kconfig.debug into lib/Kconfig.debug
- Renamed core test function arch_pgtable_tests() as debug_vm_pgtable()
- Renamed mm/arch_pgtable_test.c as mm/debug_vm_pgtable.c
- debug_vm_pgtable() gets called from kernel_init_freeable() after init_mm_internals()
- Added an entry in Documentation/features/debug/ per Ingo
- Enabled the test on arm64 and x86 platforms for now

Changes in V4: (https://patchwork.kernel.org/project/linux-mm/list/?series=183465)

- Disable DEBUG_ARCH_PGTABLE_TEST for ARM and IA64 platforms

Changes in V3: (https://lore.kernel.org/patchwork/project/lkml/list/?series=411216)

- Changed test trigger from module format into late_initcall()
- Marked all functions with __init to be freed after completion
- Changed all __PGTABLE_PXX_FOLDED checks as mm_pxx_folded()
- Folded in PPC32 fixes from Christophe

Changes in V2:

https://lore.kernel.org/linux-mm/1568268173-31302-1-git-send-email-anshuman.khandual@arm.com/T/#t

- Fixed small typo error in MODULE_DESCRIPTION()
- Fixed m64k build problems for lvalue concerns in pmd_xxx_tests()
- Fixed dynamic page table level folding problems on x86 as per Kirril
- Fixed second pointers during pxx_populate_tests() per Kirill and Gerald
- Allocate and free pte table with pte_alloc_one/pte_free per Kirill
- Modified pxx_clear_tests() to accommodate s390 lower 12 bits situation
- Changed RANDOM_NZVALUE value from 0xbe to 0xff
- Changed allocation, usage, free sequence for saved_ptep
- Renamed VMA_FLAGS as VMFLAGS
- Implemented a new method for random vaddr generation
- Implemented some other cleanups
- Dropped extern reference to mm_alloc()
- Created and exported new alloc_gigantic_page_order()
- Dropped the custom allocator and used new alloc_gigantic_page_order()

Changes in V1:

https://lore.kernel.org/linux-mm/1567497706-8649-1-git-send-email-anshuman.khandual@arm.com/

- Added fallback mechanism for PMD aligned memory allocation failure

Changes in RFC V2:

https://lore.kernel.org/linux-mm/1565335998-22553-1-git-send-email-anshuman.khandual@arm.com/T/#u

- Moved test module and it's config from lib/ to mm/
- Renamed config TEST_ARCH_PGTABLE as DEBUG_ARCH_PGTABLE_TEST
- Renamed file from test_arch_pgtable.c to arch_pgtable_test.c
- Added relevant MODULE_DESCRIPTION() and MODULE_AUTHOR() details
- Dropped loadable module config option
- Basic tests now use memory blocks with required size and alignment
- PUD aligned memory block gets allocated with alloc_contig_range()
- If PUD aligned memory could not be allocated it falls back on PMD aligned
  memory block from page allocator and pud_* tests are skipped
- Clear and populate tests now operate on real in memory page table entries
- Dummy mm_struct gets allocated with mm_alloc()
- Dummy page table entries get allocated with [pud|pmd|pte]_alloc_[map]()
- Simplified [p4d|pgd]_basic_tests(), now has random values in the entries

Original RFC V1:

https://lore.kernel.org/linux-mm/1564037723-26676-1-git-send-email-anshuman.khandual@arm.com/


 .../debug/debug-vm-pgtable/arch-support.txt   |  35 ++
 arch/arc/Kconfig                              |   1 +
 arch/arm64/Kconfig                            |   1 +
 arch/powerpc/Kconfig                          |   1 +
 arch/s390/Kconfig                             |   1 +
 arch/x86/Kconfig                              |   1 +
 arch/x86/include/asm/pgtable_64.h             |   6 +
 include/linux/mmdebug.h                       |   5 +
 init/main.c                                   |   2 +
 lib/Kconfig.debug                             |  26 ++
 mm/Makefile                                   |   1 +
 mm/debug_vm_pgtable.c                         | 389 ++++++++++++++++++
 12 files changed, 469 insertions(+)
 create mode 100644 Documentation/features/debug/debug-vm-pgtable/arch-support.txt
 create mode 100644 mm/debug_vm_pgtable.c

Comments

Anshuman Khandual Feb. 24, 2020, 1:58 a.m. UTC | #1
On 02/17/2020 08:47 AM, Anshuman Khandual wrote:
> This adds a test validation for architecture exported page table helpers.
> Patch adds basic transformation tests at various levels of the page table.
> 
> This test was originally suggested by Catalin during arm64 THP migration
> RFC discussion earlier. Going forward it can include more specific tests
> with respect to various generic MM functions like THP, HugeTLB etc and
> platform specific tests.
> 
> https://lore.kernel.org/linux-mm/20190628102003.GA56463@arrakis.emea.arm.com/
> 
> Needs to be applied on linux V5.6-rc2
> 
> Changes in V14:
> 
> - Disabled DEBUG_VM_PGFLAGS for IA64 and ARM (32 Bit) per Andrew and Christophe
> - Updated DEBUG_VM_PGFLAGS documentation wrt EXPERT and disabled platforms
> - Updated RANDOM_[OR|NZ]VALUE open encodings with GENMASK() per Catalin
> - Updated s390 constraint bits from 12 to 4 (S390_MASK_BITS) per Gerald
> - Updated in-code documentation for RANDOM_ORVALUE per Gerald
> - Updated pxx_basic_tests() to use invert functions first per Catalin
> - Dropped ARCH_HAS_4LEVEL_HACK check from pud_basic_tests()
> - Replaced __ARCH_HAS_[4|5]LEVEL_HACK with __PAGETABLE_[PUD|P4D]_FOLDED per Catalin
> - Trimmed the CC list on the commit message per Catalin

Hello Andrew,

As there are no further comments on this patch from last week, wondering
if you would possibly consider this patch. But if you feel there is still
something which need to be taken care here, please do let me know.

Thank you.

- Anshuman
Qian Cai Feb. 26, 2020, 2:09 p.m. UTC | #2
On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
> This adds tests which will validate architecture page table helpers and
> other accessors in their compliance with expected generic MM semantics.
> This will help various architectures in validating changes to existing
> page table helpers or addition of new ones.
> 
> This test covers basic page table entry transformations including but not
> limited to old, young, dirty, clean, write, write protect etc at various
> level along with populating intermediate entries with next page table page
> and validating them.
> 
> Test page table pages are allocated from system memory with required size
> and alignments. The mapped pfns at page table levels are derived from a
> real pfn representing a valid kernel text symbol. This test gets called
> inside kernel_init() right after async_synchronize_full().
> 
> This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any
> architecture, which is willing to subscribe this test will need to select
> ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390
> and ppc32 platforms where the test is known to build and run successfully.
> Going forward, other architectures too can subscribe the test after fixing
> any build or runtime problems with their page table helpers. Meanwhile for
> better platform coverage, the test can also be enabled with CONFIG_EXPERT
> even without ARCH_HAS_DEBUG_VM_PGTABLE.
> 
> Folks interested in making sure that a given platform's page table helpers
> conform to expected generic MM semantics should enable the above config
> which will just trigger this test during boot. Any non conformity here will
> be reported as an warning which would need to be fixed. This test will help
> catch any changes to the agreed upon semantics expected from generic MM and
> enable platforms to accommodate it thereafter.

How useful is this that straightly crash the powerpc?

[   23.263425][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
architecture page table helpers
[   23.263625][    T1] ------------[ cut here ]------------
[   23.263649][    T1] kernel BUG at arch/powerpc/mm/pgtable.c:274!
[   23.263675][    T1] Oops: Exception in kernel mode, sig: 5 [#1]
[   23.263698][    T1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=256
DEBUG_PAGEALLOC NUMA PowerNV
[   23.263731][    T1] Modules linked in:
[   23.263752][    T1] CPU: 4 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc3-next-
20200226 #1
[   23.263776][    T1] NIP:  c00000000007308c LR: c00000000103dbd8 CTR:
0000000000000000
[   23.263810][    T1] REGS: c00000003ddaf9c0 TRAP: 0700   Not tainted  (5.6.0-
rc3-next-20200226)
[   23.263846][    T1] MSR:  9000000000029033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR:
22000228  XER: 00000000
[   23.263888][    T1] CFAR: c000000000073030 IRQMASK: 0 
[   23.263888][    T1] GPR00: c00000000103dbd8 c00000003ddafc50 c000000001656f00
c000001d7b4ca080 
[   23.263888][    T1] GPR04: 0000000000000000 0000000000000009 c00000003ddafc04
0000000000000000 
[   23.263888][    T1] GPR08: f0ffffffffffffff 0000000000000001 c0000000016279d0
00000000000a0000 
[   23.263888][    T1] GPR12: 0000000000000000 c000001fffffae00 c000000000010e84
0000000000000000 
[   23.263888][    T1] GPR16: 0000000000000000 8000000000000105 0000000000000100
c000000001689a18 
[   23.263888][    T1] GPR20: c00020032c660000 c00020032c620000 c000000001716030
c00020032c600000 
[   23.263888][    T1] GPR24: 000000000000000d c000000001716030 c000001d7b4ca080
c000000001716040 
[   23.263888][    T1] GPR28: c000000001716038 0000000000000000 0000000000000000
0000000000000000 
[   23.264122][    T1] NIP [c00000000007308c] assert_pte_locked+0x11c/0x320
[   23.264154][    T1] LR [c00000000103dbd8] debug_vm_pgtable+0x770/0xb7c
[   23.264186][    T1] Call Trace:
[   23.264206][    T1] [c00000003ddafc50] [c000000000999760]
_raw_spin_unlock+0x30/0x70 (unreliable)
[   23.264244][    T1] [c00000003ddafcd0] [c00000000103d924]
debug_vm_pgtable+0x4bc/0xb7c
[   23.264279][    T1] [c00000003ddafdb0] [c000000000010eac]
kernel_init+0x30/0x194
[   23.264315][    T1] [c00000003ddafe20] [c00000000000b748]
ret_from_kernel_thread+0x5c/0x74
[   23.264349][    T1] Instruction dump:
[   23.264368][    T1] 60000000 3be00001 7fbef436 eafa0040 7fffc030 3bffffff
7fff07b4 7ffff038 
[   23.264409][    T1] 7bff1f24 7d37f82a 7d290074 7929d182 <0b090000> ebdb0000
e93c0000 7fde4a14 
[   23.264460][    T1] ---[ end trace 72d2931022e9ab24 ]---
[   23.627311][    T1] 
[   24.627407][    T1] Kernel panic - not syncing: Fatal exception
[   26.5

> 
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Mike Rapoport <rppt@linux.ibm.com>
> Cc: Vineet Gupta <vgupta@synopsys.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Cc: Paul Mackerras <paulus@samba.org>
> Cc: Michael Ellerman <mpe@ellerman.id.au>
> Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> Cc: Vasily Gorbik <gor@linux.ibm.com>
> Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Kirill A. Shutemov <kirill@shutemov.name>
> Cc: Paul Walmsley <paul.walmsley@sifive.com>
> Cc: Palmer Dabbelt <palmer@dabbelt.com>
> Cc: linux-snps-arc@lists.infradead.org
> Cc: linux-arm-kernel@lists.infradead.org
> Cc: linuxppc-dev@lists.ozlabs.org
> Cc: linux-s390@vger.kernel.org
> Cc: linux-riscv@lists.infradead.org
> Cc: x86@kernel.org
> Cc: linux-arch@vger.kernel.org
> Cc: linux-kernel@vger.kernel.org
> 
> Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> Reviewed-by: Ingo Molnar <mingo@kernel.org>
> Tested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>	# s390
> Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>	# ppc32
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> ---
> This adds a test validation for architecture exported page table helpers.
> Patch adds basic transformation tests at various levels of the page table.
> 
> This test was originally suggested by Catalin during arm64 THP migration
> RFC discussion earlier. Going forward it can include more specific tests
> with respect to various generic MM functions like THP, HugeTLB etc and
> platform specific tests.
> 
> https://lore.kernel.org/linux-mm/20190628102003.GA56463@arrakis.emea.arm.com/
> 
> Needs to be applied on linux V5.6-rc2
> 
> Changes in V14:
> 
> - Disabled DEBUG_VM_PGFLAGS for IA64 and ARM (32 Bit) per Andrew and Christophe
> - Updated DEBUG_VM_PGFLAGS documentation wrt EXPERT and disabled platforms
> - Updated RANDOM_[OR|NZ]VALUE open encodings with GENMASK() per Catalin
> - Updated s390 constraint bits from 12 to 4 (S390_MASK_BITS) per Gerald
> - Updated in-code documentation for RANDOM_ORVALUE per Gerald
> - Updated pxx_basic_tests() to use invert functions first per Catalin
> - Dropped ARCH_HAS_4LEVEL_HACK check from pud_basic_tests()
> - Replaced __ARCH_HAS_[4|5]LEVEL_HACK with __PAGETABLE_[PUD|P4D]_FOLDED per Catalin
> - Trimmed the CC list on the commit message per Catalin
> 
> Changes in V13: (https://patchwork.kernel.org/project/linux-mm/list/?series=237125)
> 
> - Subscribed s390 platform and updated debug-vm-pgtable/arch-support.txt per Gerald
> - Dropped keyword 'extern' from debug_vm_pgtable() declaration per Christophe
> - Moved debug_vm_pgtable() declarations to <linux/mmdebug.h> per Christophe
> - Moved debug_vm_pgtable() call site into kernel_init() per Christophe
> - Changed CONFIG_DEBUG_VM_PGTABLE rules per Christophe
> - Updated commit to include new supported platforms and changed config selection
> 
> Changes in V12: (https://patchwork.kernel.org/project/linux-mm/list/?series=233905)
> 
> - Replaced __mmdrop() with mmdrop()
> - Enable ARCH_HAS_DEBUG_VM_PGTABLE on X86 for non CONFIG_X86_PAE platforms as the
>   test procedure interfere with pre-allocated PMDs attached to the PGD resulting
>   in runtime failures with VM_BUG_ON()
> 
> Changes in V11: (https://patchwork.kernel.org/project/linux-mm/list/?series=221135)
> 
> - Rebased the patch on V5.4
> 
> Changes in V10: (https://patchwork.kernel.org/project/linux-mm/list/?series=205529)
> 
> - Always enable DEBUG_VM_PGTABLE when DEBUG_VM is enabled per Ingo
> - Added tags from Ingo
> 
> Changes in V9: (https://patchwork.kernel.org/project/linux-mm/list/?series=201429)
> 
> - Changed feature support enumeration for powerpc platforms per Christophe
> - Changed config wrapper for basic_[pmd|pud]_tests() to enable ARC platform
> - Enabled the test on ARC platform
> 
> Changes in V8: (https://patchwork.kernel.org/project/linux-mm/list/?series=194297)
> 
> - Enabled ARCH_HAS_DEBUG_VM_PGTABLE on PPC32 platform per Christophe
> - Updated feature documentation as DEBUG_VM_PGTABLE is now enabled on PPC32 platform
> - Moved ARCH_HAS_DEBUG_VM_PGTABLE earlier to indent it with DEBUG_VM per Christophe
> - Added an information message in debug_vm_pgtable() per Christophe
> - Dropped random_vaddr boundary condition checks per Christophe and Qian
> - Replaced virt_addr_valid() check with pfn_valid() check in debug_vm_pgtable()
> - Slightly changed pr_fmt(fmt) information
> 
> Changes in V7: (https://patchwork.kernel.org/project/linux-mm/list/?series=193051)
> 
> - Memory allocation and free routines for mapped pages have been droped
> - Mapped pfns are derived from standard kernel text symbol per Matthew
> - Moved debug_vm_pgtaable() after page_alloc_init_late() per Michal and Qian 
> - Updated the commit message per Michal
> - Updated W=1 GCC warning problem on x86 per Qian Cai
> - Addition of new alloc_contig_pages() helper has been submitted separately
> 
> Changes in V6: (https://patchwork.kernel.org/project/linux-mm/list/?series=187589)
> 
> - Moved alloc_gigantic_page_order() into mm/page_alloc.c per Michal
> - Moved alloc_gigantic_page_order() within CONFIG_CONTIG_ALLOC in the test
> - Folded Andrew's include/asm-generic/pgtable.h fix into the test patch 2/2
> 
> Changes in V5: (https://patchwork.kernel.org/project/linux-mm/list/?series=185991)
> 
> - Redefined and moved X86 mm_p4d_folded() into a different header per Kirill/Ingo
> - Updated the config option comment per Ingo and dropped 'kernel module' reference
> - Updated the commit message and dropped 'kernel module' reference
> - Changed DEBUG_ARCH_PGTABLE_TEST into DEBUG_VM_PGTABLE per Ingo
> - Moved config option from mm/Kconfig.debug into lib/Kconfig.debug
> - Renamed core test function arch_pgtable_tests() as debug_vm_pgtable()
> - Renamed mm/arch_pgtable_test.c as mm/debug_vm_pgtable.c
> - debug_vm_pgtable() gets called from kernel_init_freeable() after init_mm_internals()
> - Added an entry in Documentation/features/debug/ per Ingo
> - Enabled the test on arm64 and x86 platforms for now
> 
> Changes in V4: (https://patchwork.kernel.org/project/linux-mm/list/?series=183465)
> 
> - Disable DEBUG_ARCH_PGTABLE_TEST for ARM and IA64 platforms
> 
> Changes in V3: (https://lore.kernel.org/patchwork/project/lkml/list/?series=411216)
> 
> - Changed test trigger from module format into late_initcall()
> - Marked all functions with __init to be freed after completion
> - Changed all __PGTABLE_PXX_FOLDED checks as mm_pxx_folded()
> - Folded in PPC32 fixes from Christophe
> 
> Changes in V2:
> 
> https://lore.kernel.org/linux-mm/1568268173-31302-1-git-send-email-anshuman.khandual@arm.com/T/#t
> 
> - Fixed small typo error in MODULE_DESCRIPTION()
> - Fixed m64k build problems for lvalue concerns in pmd_xxx_tests()
> - Fixed dynamic page table level folding problems on x86 as per Kirril
> - Fixed second pointers during pxx_populate_tests() per Kirill and Gerald
> - Allocate and free pte table with pte_alloc_one/pte_free per Kirill
> - Modified pxx_clear_tests() to accommodate s390 lower 12 bits situation
> - Changed RANDOM_NZVALUE value from 0xbe to 0xff
> - Changed allocation, usage, free sequence for saved_ptep
> - Renamed VMA_FLAGS as VMFLAGS
> - Implemented a new method for random vaddr generation
> - Implemented some other cleanups
> - Dropped extern reference to mm_alloc()
> - Created and exported new alloc_gigantic_page_order()
> - Dropped the custom allocator and used new alloc_gigantic_page_order()
> 
> Changes in V1:
> 
> https://lore.kernel.org/linux-mm/1567497706-8649-1-git-send-email-anshuman.khandual@arm.com/
> 
> - Added fallback mechanism for PMD aligned memory allocation failure
> 
> Changes in RFC V2:
> 
> https://lore.kernel.org/linux-mm/1565335998-22553-1-git-send-email-anshuman.khandual@arm.com/T/#u
> 
> - Moved test module and it's config from lib/ to mm/
> - Renamed config TEST_ARCH_PGTABLE as DEBUG_ARCH_PGTABLE_TEST
> - Renamed file from test_arch_pgtable.c to arch_pgtable_test.c
> - Added relevant MODULE_DESCRIPTION() and MODULE_AUTHOR() details
> - Dropped loadable module config option
> - Basic tests now use memory blocks with required size and alignment
> - PUD aligned memory block gets allocated with alloc_contig_range()
> - If PUD aligned memory could not be allocated it falls back on PMD aligned
>   memory block from page allocator and pud_* tests are skipped
> - Clear and populate tests now operate on real in memory page table entries
> - Dummy mm_struct gets allocated with mm_alloc()
> - Dummy page table entries get allocated with [pud|pmd|pte]_alloc_[map]()
> - Simplified [p4d|pgd]_basic_tests(), now has random values in the entries
> 
> Original RFC V1:
> 
> https://lore.kernel.org/linux-mm/1564037723-26676-1-git-send-email-anshuman.khandual@arm.com/
> 
> 
>  .../debug/debug-vm-pgtable/arch-support.txt   |  35 ++
>  arch/arc/Kconfig                              |   1 +
>  arch/arm64/Kconfig                            |   1 +
>  arch/powerpc/Kconfig                          |   1 +
>  arch/s390/Kconfig                             |   1 +
>  arch/x86/Kconfig                              |   1 +
>  arch/x86/include/asm/pgtable_64.h             |   6 +
>  include/linux/mmdebug.h                       |   5 +
>  init/main.c                                   |   2 +
>  lib/Kconfig.debug                             |  26 ++
>  mm/Makefile                                   |   1 +
>  mm/debug_vm_pgtable.c                         | 389 ++++++++++++++++++
>  12 files changed, 469 insertions(+)
>  create mode 100644 Documentation/features/debug/debug-vm-pgtable/arch-support.txt
>  create mode 100644 mm/debug_vm_pgtable.c
> 
> diff --git a/Documentation/features/debug/debug-vm-pgtable/arch-support.txt b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
> new file mode 100644
> index 000000000000..64d0f9b15c49
> --- /dev/null
> +++ b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
> @@ -0,0 +1,35 @@
> +#
> +# Feature name:          debug-vm-pgtable
> +#         Kconfig:       ARCH_HAS_DEBUG_VM_PGTABLE
> +#         description:   arch supports pgtable tests for semantics compliance
> +#
> +    -----------------------
> +    |         arch |status|
> +    -----------------------
> +    |       alpha: | TODO |
> +    |         arc: |  ok  |
> +    |         arm: | TODO |
> +    |       arm64: |  ok  |
> +    |         c6x: | TODO |
> +    |        csky: | TODO |
> +    |       h8300: | TODO |
> +    |     hexagon: | TODO |
> +    |        ia64: | TODO |
> +    |        m68k: | TODO |
> +    |  microblaze: | TODO |
> +    |        mips: | TODO |
> +    |       nds32: | TODO |
> +    |       nios2: | TODO |
> +    |    openrisc: | TODO |
> +    |      parisc: | TODO |
> +    |  powerpc/32: |  ok  |
> +    |  powerpc/64: | TODO |
> +    |       riscv: | TODO |
> +    |        s390: |  ok  |
> +    |          sh: | TODO |
> +    |       sparc: | TODO |
> +    |          um: | TODO |
> +    |   unicore32: | TODO |
> +    |         x86: |  ok  |
> +    |      xtensa: | TODO |
> +    -----------------------
> diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> index ff2a393b635c..3e72e6cf0e42 100644
> --- a/arch/arc/Kconfig
> +++ b/arch/arc/Kconfig
> @@ -6,6 +6,7 @@
>  config ARC
>  	def_bool y
>  	select ARC_TIMERS
> +	select ARCH_HAS_DEBUG_VM_PGTABLE
>  	select ARCH_HAS_DMA_PREP_COHERENT
>  	select ARCH_HAS_PTE_SPECIAL
>  	select ARCH_HAS_SETUP_DMA_OPS
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 0b30e884e088..aaf8ba415145 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -11,6 +11,7 @@ config ARM64
>  	select ACPI_PPTT if ACPI
>  	select ARCH_CLOCKSOURCE_DATA
>  	select ARCH_HAS_DEBUG_VIRTUAL
> +	select ARCH_HAS_DEBUG_VM_PGTABLE
>  	select ARCH_HAS_DEVMEM_IS_ALLOWED
>  	select ARCH_HAS_DMA_PREP_COHERENT
>  	select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
> diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> index 497b7d0b2d7e..8d5ae14c5d4c 100644
> --- a/arch/powerpc/Kconfig
> +++ b/arch/powerpc/Kconfig
> @@ -116,6 +116,7 @@ config PPC
>  	#
>  	select ARCH_32BIT_OFF_T if PPC32
>  	select ARCH_HAS_DEBUG_VIRTUAL
> +	select ARCH_HAS_DEBUG_VM_PGTABLE if PPC32
>  	select ARCH_HAS_DEVMEM_IS_ALLOWED
>  	select ARCH_HAS_ELF_RANDOMIZE
>  	select ARCH_HAS_FORTIFY_SOURCE
> diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> index 8abe77536d9d..af284dbb07e7 100644
> --- a/arch/s390/Kconfig
> +++ b/arch/s390/Kconfig
> @@ -59,6 +59,7 @@ config KASAN_SHADOW_OFFSET
>  config S390
>  	def_bool y
>  	select ARCH_BINFMT_ELF_STATE
> +	select ARCH_HAS_DEBUG_VM_PGTABLE
>  	select ARCH_HAS_DEVMEM_IS_ALLOWED
>  	select ARCH_HAS_ELF_RANDOMIZE
>  	select ARCH_HAS_FORTIFY_SOURCE
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index beea77046f9b..df8a19e52e82 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -61,6 +61,7 @@ config X86
>  	select ARCH_CLOCKSOURCE_INIT
>  	select ARCH_HAS_ACPI_TABLE_UPGRADE	if ACPI
>  	select ARCH_HAS_DEBUG_VIRTUAL
> +	select ARCH_HAS_DEBUG_VM_PGTABLE	if !X86_PAE
>  	select ARCH_HAS_DEVMEM_IS_ALLOWED
>  	select ARCH_HAS_ELF_RANDOMIZE
>  	select ARCH_HAS_FAST_MULTIPLIER
> diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
> index 0b6c4042942a..fb0e76d254b3 100644
> --- a/arch/x86/include/asm/pgtable_64.h
> +++ b/arch/x86/include/asm/pgtable_64.h
> @@ -53,6 +53,12 @@ static inline void sync_initial_page_table(void) { }
>  
>  struct mm_struct;
>  
> +#define mm_p4d_folded mm_p4d_folded
> +static inline bool mm_p4d_folded(struct mm_struct *mm)
> +{
> +	return !pgtable_l5_enabled();
> +}
> +
>  void set_pte_vaddr_p4d(p4d_t *p4d_page, unsigned long vaddr, pte_t new_pte);
>  void set_pte_vaddr_pud(pud_t *pud_page, unsigned long vaddr, pte_t new_pte);
>  
> diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> index 2ad72d2c8cc5..5339aa14b749 100644
> --- a/include/linux/mmdebug.h
> +++ b/include/linux/mmdebug.h
> @@ -64,4 +64,9 @@ void dump_mm(const struct mm_struct *mm);
>  #define VM_BUG_ON_PGFLAGS(cond, page) BUILD_BUG_ON_INVALID(cond)
>  #endif
>  
> +#ifdef CONFIG_DEBUG_VM_PGTABLE
> +void debug_vm_pgtable(void);
> +#else
> +static inline void debug_vm_pgtable(void) { }
> +#endif
>  #endif
> diff --git a/init/main.c b/init/main.c
> index cc0ee4873419..adf37e8b1d69 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -94,6 +94,7 @@
>  #include <linux/rodata_test.h>
>  #include <linux/jump_label.h>
>  #include <linux/mem_encrypt.h>
> +#include <linux/mmdebug.h>
>  
>  #include <asm/io.h>
>  #include <asm/bugs.h>
> @@ -1323,6 +1324,7 @@ static int __ref kernel_init(void *unused)
>  	kernel_init_freeable();
>  	/* need to finish all async __init code before freeing the memory */
>  	async_synchronize_full();
> +	debug_vm_pgtable();
>  	ftrace_free_init_mem();
>  	free_initmem();
>  	mark_readonly();
> diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> index 69def4a9df00..1b5bd9f7c967 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -653,6 +653,12 @@ config SCHED_STACK_END_CHECK
>  	  data corruption or a sporadic crash at a later stage once the region
>  	  is examined. The runtime overhead introduced is minimal.
>  
> +config ARCH_HAS_DEBUG_VM_PGTABLE
> +	bool
> +	help
> +	  An architecture should select this when it can successfully
> +	  build and run DEBUG_VM_PGTABLE.
> +
>  config DEBUG_VM
>  	bool "Debug VM"
>  	depends on DEBUG_KERNEL
> @@ -688,6 +694,26 @@ config DEBUG_VM_PGFLAGS
>  
>  	  If unsure, say N.
>  
> +config DEBUG_VM_PGTABLE
> +	bool "Debug arch page table for semantics compliance"
> +	depends on MMU
> +	depends on !IA64 && !ARM
> +	depends on ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
> +	default n if !ARCH_HAS_DEBUG_VM_PGTABLE
> +	default y if DEBUG_VM
> +	help
> +	  This option provides a debug method which can be used to test
> +	  architecture page table helper functions on various platforms in
> +	  verifying if they comply with expected generic MM semantics. This
> +	  will help architecture code in making sure that any changes or
> +	  new additions of these helpers still conform to expected
> +	  semantics of the generic MM. Platforms will have to opt in for
> +	  this through ARCH_HAS_DEBUG_VM_PGTABLE. Although it can also be
> +	  enabled through EXPERT without requiring code change. This test
> +	  is disabled on IA64 and ARM platforms where it fails to build.
> +
> +	  If unsure, say N.
> +
>  config ARCH_HAS_DEBUG_VIRTUAL
>  	bool
>  
> diff --git a/mm/Makefile b/mm/Makefile
> index 272e66039e70..b0692e6a4b58 100644
> --- a/mm/Makefile
> +++ b/mm/Makefile
> @@ -87,6 +87,7 @@ obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
>  obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
>  obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
>  obj-$(CONFIG_DEBUG_RODATA_TEST) += rodata_test.o
> +obj-$(CONFIG_DEBUG_VM_PGTABLE) += debug_vm_pgtable.o
>  obj-$(CONFIG_PAGE_OWNER) += page_owner.o
>  obj-$(CONFIG_CLEANCACHE) += cleancache.o
>  obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> new file mode 100644
> index 000000000000..70bf8ed8fd51
> --- /dev/null
> +++ b/mm/debug_vm_pgtable.c
> @@ -0,0 +1,389 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * This kernel test validates architecture page table helpers and
> + * accessors and helps in verifying their continued compliance with
> + * expected generic MM semantics.
> + *
> + * Copyright (C) 2019 ARM Ltd.
> + *
> + * Author: Anshuman Khandual <anshuman.khandual@arm.com>
> + */
> +#define pr_fmt(fmt) "debug_vm_pgtable: %s: " fmt, __func__
> +
> +#include <linux/gfp.h>
> +#include <linux/highmem.h>
> +#include <linux/hugetlb.h>
> +#include <linux/kernel.h>
> +#include <linux/kconfig.h>
> +#include <linux/mm.h>
> +#include <linux/mman.h>
> +#include <linux/mm_types.h>
> +#include <linux/module.h>
> +#include <linux/pfn_t.h>
> +#include <linux/printk.h>
> +#include <linux/random.h>
> +#include <linux/spinlock.h>
> +#include <linux/swap.h>
> +#include <linux/swapops.h>
> +#include <linux/start_kernel.h>
> +#include <linux/sched/mm.h>
> +#include <asm/pgalloc.h>
> +#include <asm/pgtable.h>
> +
> +/*
> + * Basic operations
> + *
> + * mkold(entry)			= An old and not a young entry
> + * mkyoung(entry)		= A young and not an old entry
> + * mkdirty(entry)		= A dirty and not a clean entry
> + * mkclean(entry)		= A clean and not a dirty entry
> + * mkwrite(entry)		= A write and not a write protected entry
> + * wrprotect(entry)		= A write protected and not a write entry
> + * pxx_bad(entry)		= A mapped and non-table entry
> + * pxx_same(entry1, entry2)	= Both entries hold the exact same value
> + */
> +#define VMFLAGS	(VM_READ|VM_WRITE|VM_EXEC)
> +
> +/*
> + * On s390 platform, the lower 4 bits are used to identify given page table
> + * entry type. But these bits might affect the ability to clear entries with
> + * pxx_clear() because of how dynamic page table folding works on s390. So
> + * while loading up the entries do not change the lower 4 bits. It does not
> + * have affect any other platform.
> + */
> +#define S390_MASK_BITS	4
> +#define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
> +#define RANDOM_NZVALUE	GENMASK(7, 0)
> +
> +static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
> +{
> +	pte_t pte = pfn_pte(pfn, prot);
> +
> +	WARN_ON(!pte_same(pte, pte));
> +	WARN_ON(!pte_young(pte_mkyoung(pte_mkold(pte))));
> +	WARN_ON(!pte_dirty(pte_mkdirty(pte_mkclean(pte))));
> +	WARN_ON(!pte_write(pte_mkwrite(pte_wrprotect(pte))));
> +	WARN_ON(pte_young(pte_mkold(pte_mkyoung(pte))));
> +	WARN_ON(pte_dirty(pte_mkclean(pte_mkdirty(pte))));
> +	WARN_ON(pte_write(pte_wrprotect(pte_mkwrite(pte))));
> +}
> +
> +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> +static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot)
> +{
> +	pmd_t pmd = pfn_pmd(pfn, prot);
> +
> +	WARN_ON(!pmd_same(pmd, pmd));
> +	WARN_ON(!pmd_young(pmd_mkyoung(pmd_mkold(pmd))));
> +	WARN_ON(!pmd_dirty(pmd_mkdirty(pmd_mkclean(pmd))));
> +	WARN_ON(!pmd_write(pmd_mkwrite(pmd_wrprotect(pmd))));
> +	WARN_ON(pmd_young(pmd_mkold(pmd_mkyoung(pmd))));
> +	WARN_ON(pmd_dirty(pmd_mkclean(pmd_mkdirty(pmd))));
> +	WARN_ON(pmd_write(pmd_wrprotect(pmd_mkwrite(pmd))));
> +	/*
> +	 * A huge page does not point to next level page table
> +	 * entry. Hence this must qualify as pmd_bad().
> +	 */
> +	WARN_ON(!pmd_bad(pmd_mkhuge(pmd)));
> +}
> +
> +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> +static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot)
> +{
> +	pud_t pud = pfn_pud(pfn, prot);
> +
> +	WARN_ON(!pud_same(pud, pud));
> +	WARN_ON(!pud_young(pud_mkyoung(pud_mkold(pud))));
> +	WARN_ON(!pud_write(pud_mkwrite(pud_wrprotect(pud))));
> +	WARN_ON(pud_write(pud_wrprotect(pud_mkwrite(pud))));
> +	WARN_ON(pud_young(pud_mkold(pud_mkyoung(pud))));
> +
> +	if (mm_pmd_folded(mm))
> +		return;
> +
> +	/*
> +	 * A huge page does not point to next level page table
> +	 * entry. Hence this must qualify as pud_bad().
> +	 */
> +	WARN_ON(!pud_bad(pud_mkhuge(pud)));
> +}
> +#else
> +static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) { }
> +#endif
> +#else
> +static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot) { }
> +static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) { }
> +#endif
> +
> +static void __init p4d_basic_tests(unsigned long pfn, pgprot_t prot)
> +{
> +	p4d_t p4d;
> +
> +	memset(&p4d, RANDOM_NZVALUE, sizeof(p4d_t));
> +	WARN_ON(!p4d_same(p4d, p4d));
> +}
> +
> +static void __init pgd_basic_tests(unsigned long pfn, pgprot_t prot)
> +{
> +	pgd_t pgd;
> +
> +	memset(&pgd, RANDOM_NZVALUE, sizeof(pgd_t));
> +	WARN_ON(!pgd_same(pgd, pgd));
> +}
> +
> +#ifndef __PAGETABLE_PUD_FOLDED
> +static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp)
> +{
> +	pud_t pud = READ_ONCE(*pudp);
> +
> +	if (mm_pmd_folded(mm))
> +		return;
> +
> +	pud = __pud(pud_val(pud) | RANDOM_ORVALUE);
> +	WRITE_ONCE(*pudp, pud);
> +	pud_clear(pudp);
> +	pud = READ_ONCE(*pudp);
> +	WARN_ON(!pud_none(pud));
> +}
> +
> +static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
> +				      pmd_t *pmdp)
> +{
> +	pud_t pud;
> +
> +	if (mm_pmd_folded(mm))
> +		return;
> +	/*
> +	 * This entry points to next level page table page.
> +	 * Hence this must not qualify as pud_bad().
> +	 */
> +	pmd_clear(pmdp);
> +	pud_clear(pudp);
> +	pud_populate(mm, pudp, pmdp);
> +	pud = READ_ONCE(*pudp);
> +	WARN_ON(pud_bad(pud));
> +}
> +#else
> +static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp) { }
> +static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
> +				      pmd_t *pmdp)
> +{
> +}
> +#endif
> +
> +#ifndef __PAGETABLE_P4D_FOLDED
> +static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp)
> +{
> +	p4d_t p4d = READ_ONCE(*p4dp);
> +
> +	if (mm_pud_folded(mm))
> +		return;
> +
> +	p4d = __p4d(p4d_val(p4d) | RANDOM_ORVALUE);
> +	WRITE_ONCE(*p4dp, p4d);
> +	p4d_clear(p4dp);
> +	p4d = READ_ONCE(*p4dp);
> +	WARN_ON(!p4d_none(p4d));
> +}
> +
> +static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
> +				      pud_t *pudp)
> +{
> +	p4d_t p4d;
> +
> +	if (mm_pud_folded(mm))
> +		return;
> +
> +	/*
> +	 * This entry points to next level page table page.
> +	 * Hence this must not qualify as p4d_bad().
> +	 */
> +	pud_clear(pudp);
> +	p4d_clear(p4dp);
> +	p4d_populate(mm, p4dp, pudp);
> +	p4d = READ_ONCE(*p4dp);
> +	WARN_ON(p4d_bad(p4d));
> +}
> +
> +static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp)
> +{
> +	pgd_t pgd = READ_ONCE(*pgdp);
> +
> +	if (mm_p4d_folded(mm))
> +		return;
> +
> +	pgd = __pgd(pgd_val(pgd) | RANDOM_ORVALUE);
> +	WRITE_ONCE(*pgdp, pgd);
> +	pgd_clear(pgdp);
> +	pgd = READ_ONCE(*pgdp);
> +	WARN_ON(!pgd_none(pgd));
> +}
> +
> +static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
> +				      p4d_t *p4dp)
> +{
> +	pgd_t pgd;
> +
> +	if (mm_p4d_folded(mm))
> +		return;
> +
> +	/*
> +	 * This entry points to next level page table page.
> +	 * Hence this must not qualify as pgd_bad().
> +	 */
> +	p4d_clear(p4dp);
> +	pgd_clear(pgdp);
> +	pgd_populate(mm, pgdp, p4dp);
> +	pgd = READ_ONCE(*pgdp);
> +	WARN_ON(pgd_bad(pgd));
> +}
> +#else
> +static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp) { }
> +static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp) { }
> +static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
> +				      pud_t *pudp)
> +{
> +}
> +static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
> +				      p4d_t *p4dp)
> +{
> +}
> +#endif
> +
> +static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)
> +{
> +	pte_t pte = READ_ONCE(*ptep);
> +
> +	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
> +	WRITE_ONCE(*ptep, pte);
> +	pte_clear(mm, 0, ptep);
> +	pte = READ_ONCE(*ptep);
> +	WARN_ON(!pte_none(pte));
> +}
> +
> +static void __init pmd_clear_tests(struct mm_struct *mm, pmd_t *pmdp)
> +{
> +	pmd_t pmd = READ_ONCE(*pmdp);
> +
> +	pmd = __pmd(pmd_val(pmd) | RANDOM_ORVALUE);
> +	WRITE_ONCE(*pmdp, pmd);
> +	pmd_clear(pmdp);
> +	pmd = READ_ONCE(*pmdp);
> +	WARN_ON(!pmd_none(pmd));
> +}
> +
> +static void __init pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
> +				      pgtable_t pgtable)
> +{
> +	pmd_t pmd;
> +
> +	/*
> +	 * This entry points to next level page table page.
> +	 * Hence this must not qualify as pmd_bad().
> +	 */
> +	pmd_clear(pmdp);
> +	pmd_populate(mm, pmdp, pgtable);
> +	pmd = READ_ONCE(*pmdp);
> +	WARN_ON(pmd_bad(pmd));
> +}
> +
> +static unsigned long __init get_random_vaddr(void)
> +{
> +	unsigned long random_vaddr, random_pages, total_user_pages;
> +
> +	total_user_pages = (TASK_SIZE - FIRST_USER_ADDRESS) / PAGE_SIZE;
> +
> +	random_pages = get_random_long() % total_user_pages;
> +	random_vaddr = FIRST_USER_ADDRESS + random_pages * PAGE_SIZE;
> +
> +	return random_vaddr;
> +}
> +
> +void __init debug_vm_pgtable(void)
> +{
> +	struct mm_struct *mm;
> +	pgd_t *pgdp;
> +	p4d_t *p4dp, *saved_p4dp;
> +	pud_t *pudp, *saved_pudp;
> +	pmd_t *pmdp, *saved_pmdp, pmd;
> +	pte_t *ptep;
> +	pgtable_t saved_ptep;
> +	pgprot_t prot;
> +	phys_addr_t paddr;
> +	unsigned long vaddr, pte_aligned, pmd_aligned;
> +	unsigned long pud_aligned, p4d_aligned, pgd_aligned;
> +
> +	pr_info("Validating architecture page table helpers\n");
> +	prot = vm_get_page_prot(VMFLAGS);
> +	vaddr = get_random_vaddr();
> +	mm = mm_alloc();
> +	if (!mm) {
> +		pr_err("mm_struct allocation failed\n");
> +		return;
> +	}
> +
> +	/*
> +	 * PFN for mapping at PTE level is determined from a standard kernel
> +	 * text symbol. But pfns for higher page table levels are derived by
> +	 * masking lower bits of this real pfn. These derived pfns might not
> +	 * exist on the platform but that does not really matter as pfn_pxx()
> +	 * helpers will still create appropriate entries for the test. This
> +	 * helps avoid large memory block allocations to be used for mapping
> +	 * at higher page table levels.
> +	 */
> +	paddr = __pa(&start_kernel);
> +
> +	pte_aligned = (paddr & PAGE_MASK) >> PAGE_SHIFT;
> +	pmd_aligned = (paddr & PMD_MASK) >> PAGE_SHIFT;
> +	pud_aligned = (paddr & PUD_MASK) >> PAGE_SHIFT;
> +	p4d_aligned = (paddr & P4D_MASK) >> PAGE_SHIFT;
> +	pgd_aligned = (paddr & PGDIR_MASK) >> PAGE_SHIFT;
> +	WARN_ON(!pfn_valid(pte_aligned));
> +
> +	pgdp = pgd_offset(mm, vaddr);
> +	p4dp = p4d_alloc(mm, pgdp, vaddr);
> +	pudp = pud_alloc(mm, p4dp, vaddr);
> +	pmdp = pmd_alloc(mm, pudp, vaddr);
> +	ptep = pte_alloc_map(mm, pmdp, vaddr);
> +
> +	/*
> +	 * Save all the page table page addresses as the page table
> +	 * entries will be used for testing with random or garbage
> +	 * values. These saved addresses will be used for freeing
> +	 * page table pages.
> +	 */
> +	pmd = READ_ONCE(*pmdp);
> +	saved_p4dp = p4d_offset(pgdp, 0UL);
> +	saved_pudp = pud_offset(p4dp, 0UL);
> +	saved_pmdp = pmd_offset(pudp, 0UL);
> +	saved_ptep = pmd_pgtable(pmd);
> +
> +	pte_basic_tests(pte_aligned, prot);
> +	pmd_basic_tests(pmd_aligned, prot);
> +	pud_basic_tests(pud_aligned, prot);
> +	p4d_basic_tests(p4d_aligned, prot);
> +	pgd_basic_tests(pgd_aligned, prot);
> +
> +	pte_clear_tests(mm, ptep);
> +	pmd_clear_tests(mm, pmdp);
> +	pud_clear_tests(mm, pudp);
> +	p4d_clear_tests(mm, p4dp);
> +	pgd_clear_tests(mm, pgdp);
> +
> +	pte_unmap(ptep);
> +
> +	pmd_populate_tests(mm, pmdp, saved_ptep);
> +	pud_populate_tests(mm, pudp, saved_pmdp);
> +	p4d_populate_tests(mm, p4dp, saved_pudp);
> +	pgd_populate_tests(mm, pgdp, saved_p4dp);
> +
> +	p4d_free(mm, saved_p4dp);
> +	pud_free(mm, saved_pudp);
> +	pmd_free(mm, saved_pmdp);
> +	pte_free(mm, saved_ptep);
> +
> +	mm_dec_nr_puds(mm);
> +	mm_dec_nr_pmds(mm);
> +	mm_dec_nr_ptes(mm);
> +	mmdrop(mm);
> +}
Qian Cai Feb. 26, 2020, 2:12 p.m. UTC | #3
On Wed, 2020-02-26 at 09:09 -0500, Qian Cai wrote:
> On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
> > This adds tests which will validate architecture page table helpers and
> > other accessors in their compliance with expected generic MM semantics.
> > This will help various architectures in validating changes to existing
> > page table helpers or addition of new ones.
> > 
> > This test covers basic page table entry transformations including but not
> > limited to old, young, dirty, clean, write, write protect etc at various
> > level along with populating intermediate entries with next page table page
> > and validating them.
> > 
> > Test page table pages are allocated from system memory with required size
> > and alignments. The mapped pfns at page table levels are derived from a
> > real pfn representing a valid kernel text symbol. This test gets called
> > inside kernel_init() right after async_synchronize_full().
> > 
> > This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any
> > architecture, which is willing to subscribe this test will need to select
> > ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390
> > and ppc32 platforms where the test is known to build and run successfully.
> > Going forward, other architectures too can subscribe the test after fixing
> > any build or runtime problems with their page table helpers. Meanwhile for
> > better platform coverage, the test can also be enabled with CONFIG_EXPERT
> > even without ARCH_HAS_DEBUG_VM_PGTABLE.
> > 
> > Folks interested in making sure that a given platform's page table helpers
> > conform to expected generic MM semantics should enable the above config
> > which will just trigger this test during boot. Any non conformity here will
> > be reported as an warning which would need to be fixed. This test will help
> > catch any changes to the agreed upon semantics expected from generic MM and
> > enable platforms to accommodate it thereafter.
> 
> How useful is this that straightly crash the powerpc?

And then generate warnings on arm64,

[  146.634626][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
architecture page table helpers
[  146.643995][    T1] ------------[ cut here ]------------
[  146.649350][    T1] virt_to_phys used for non-linear address:
(____ptrval____) (start_kernel+0x0/0x580)
[  146.658840][    T1] WARNING: CPU: 165 PID: 1 at arch/arm64/mm/physaddr.c:15
__virt_to_phys+0x98/0xe0
[  146.667976][    T1] Modules linked in:
[  146.671741][    T1] CPU: 165 PID: 1 Comm: swapper/0 Tainted:
G             L    5.6.0-rc3-next-20200226 #1
[  146.681397][    T1] Hardware name: HPE Apollo
70             /C01_APACHE_MB         , BIOS L50_5.13_1.11 06/18/2019
[  146.691840][    T1] pstate: 60400009 (nZCv daif +PAN -UAO)
[  146.697334][    T1] pc : __virt_to_phys+0x98/0xe0
[  146.702045][    T1] lr : __virt_to_phys+0x98/0xe0
[  146.706753][    T1] sp : 18ff00082b7afe10
[  146.710766][    T1] x29: 18ff00082b7afe30 x28: 0000000000000000 
[  146.716782][    T1] x27: 0000000000000000 x26: 0000000000000000 
[  146.722798][    T1] x25: 0000000000000000 x24: 0000000000000000 
[  146.728813][    T1] x23: 0000000000000000 x22: 0000000000000000 
[  146.734827][    T1] x21: 0000000000000000 x20: ffff9000135b4000 
[  146.740842][    T1] x19: ffff900011200858 x18: 0000000000000000 
[  146.746857][    T1] x17: 0000000000000000 x16: 0000000000000000 
[  146.752872][    T1] x15: 0000000000000000 x14: 3078302b6c656e72 
[  146.758887][    T1] x13: 656b5f7472617473 x12: ffff90001369ea90 
[  146.764901][    T1] x11: 00000000000000c9 x10: ffff800082b76c0e 
[  146.770917][    T1] x9 : 9d6a2e2260401300 x8 : 9d6a2e2260401300 
[  146.776932][    T1] x7 : aaaaaaaaaaaaaaaa x6 : 0000000000000000 
[  146.782946][    T1] x5 : 0000000000000080 x4 : 0000000000000000 
[  146.788960][    T1] x3 : 0000000000000010 x2 : 0000000000000008 
[  146.794975][    T1] x1 : 0000000000000006 x0 : 0000000000000053 
[  146.800990][    T1] Call trace:
[  146.804140][    T1]  __virt_to_phys+0x98/0xe0
[  146.808512][    T1]  debug_vm_pgtable+0x74/0x3fc
[  146.813140][    T1]  kernel_init+0x1c/0x208
[  146.817334][    T1]  ret_from_fork+0x10/0x18
[  146.821608][    T1] irq event stamp: 19843388
[  146.825978][    T1] hardirqs last  enabled at (19843387):
[<ffff9000101d959c>] console_unlock+0x8d0/0x970
[  146.835553][    T1] hardirqs last disabled at (19843388):
[<ffff9000100ad0e0>] do_debug_exception+0x58/0x2cc
[  146.845387][    T1] softirqs last  enabled at (19843384):
[<ffff900010081b8c>] __do_softirq+0x864/0x900
[  146.854796][    T1] softirqs last disabled at (19843377):
[<ffff900010120b70>] irq_exit+0x1c8/0x238
[  146.863845][    T1] ---[ end trace 31678d9e845dff89 ]---

> 
> [   23.263425][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
> architecture page table helpers
> [   23.263625][    T1] ------------[ cut here ]------------
> [   23.263649][    T1] kernel BUG at arch/powerpc/mm/pgtable.c:274!
> [   23.263675][    T1] Oops: Exception in kernel mode, sig: 5 [#1]
> [   23.263698][    T1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=256
> DEBUG_PAGEALLOC NUMA PowerNV
> [   23.263731][    T1] Modules linked in:
> [   23.263752][    T1] CPU: 4 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc3-next-
> 20200226 #1
> [   23.263776][    T1] NIP:  c00000000007308c LR: c00000000103dbd8 CTR:
> 0000000000000000
> [   23.263810][    T1] REGS: c00000003ddaf9c0 TRAP: 0700   Not tainted  (5.6.0-
> rc3-next-20200226)
> [   23.263846][    T1] MSR:  9000000000029033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR:
> 22000228  XER: 00000000
> [   23.263888][    T1] CFAR: c000000000073030 IRQMASK: 0 
> [   23.263888][    T1] GPR00: c00000000103dbd8 c00000003ddafc50 c000000001656f00
> c000001d7b4ca080 
> [   23.263888][    T1] GPR04: 0000000000000000 0000000000000009 c00000003ddafc04
> 0000000000000000 
> [   23.263888][    T1] GPR08: f0ffffffffffffff 0000000000000001 c0000000016279d0
> 00000000000a0000 
> [   23.263888][    T1] GPR12: 0000000000000000 c000001fffffae00 c000000000010e84
> 0000000000000000 
> [   23.263888][    T1] GPR16: 0000000000000000 8000000000000105 0000000000000100
> c000000001689a18 
> [   23.263888][    T1] GPR20: c00020032c660000 c00020032c620000 c000000001716030
> c00020032c600000 
> [   23.263888][    T1] GPR24: 000000000000000d c000000001716030 c000001d7b4ca080
> c000000001716040 
> [   23.263888][    T1] GPR28: c000000001716038 0000000000000000 0000000000000000
> 0000000000000000 
> [   23.264122][    T1] NIP [c00000000007308c] assert_pte_locked+0x11c/0x320
> [   23.264154][    T1] LR [c00000000103dbd8] debug_vm_pgtable+0x770/0xb7c
> [   23.264186][    T1] Call Trace:
> [   23.264206][    T1] [c00000003ddafc50] [c000000000999760]
> _raw_spin_unlock+0x30/0x70 (unreliable)
> [   23.264244][    T1] [c00000003ddafcd0] [c00000000103d924]
> debug_vm_pgtable+0x4bc/0xb7c
> [   23.264279][    T1] [c00000003ddafdb0] [c000000000010eac]
> kernel_init+0x30/0x194
> [   23.264315][    T1] [c00000003ddafe20] [c00000000000b748]
> ret_from_kernel_thread+0x5c/0x74
> [   23.264349][    T1] Instruction dump:
> [   23.264368][    T1] 60000000 3be00001 7fbef436 eafa0040 7fffc030 3bffffff
> 7fff07b4 7ffff038 
> [   23.264409][    T1] 7bff1f24 7d37f82a 7d290074 7929d182 <0b090000> ebdb0000
> e93c0000 7fde4a14 
> [   23.264460][    T1] ---[ end trace 72d2931022e9ab24 ]---
> [   23.627311][    T1] 
> [   24.627407][    T1] Kernel panic - not syncing: Fatal exception
> [   26.5
> 
> > 
> > Cc: Andrew Morton <akpm@linux-foundation.org>
> > Cc: Mike Rapoport <rppt@linux.ibm.com>
> > Cc: Vineet Gupta <vgupta@synopsys.com>
> > Cc: Catalin Marinas <catalin.marinas@arm.com>
> > Cc: Will Deacon <will@kernel.org>
> > Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> > Cc: Paul Mackerras <paulus@samba.org>
> > Cc: Michael Ellerman <mpe@ellerman.id.au>
> > Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
> > Cc: Vasily Gorbik <gor@linux.ibm.com>
> > Cc: Christian Borntraeger <borntraeger@de.ibm.com>
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Borislav Petkov <bp@alien8.de>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: Kirill A. Shutemov <kirill@shutemov.name>
> > Cc: Paul Walmsley <paul.walmsley@sifive.com>
> > Cc: Palmer Dabbelt <palmer@dabbelt.com>
> > Cc: linux-snps-arc@lists.infradead.org
> > Cc: linux-arm-kernel@lists.infradead.org
> > Cc: linuxppc-dev@lists.ozlabs.org
> > Cc: linux-s390@vger.kernel.org
> > Cc: linux-riscv@lists.infradead.org
> > Cc: x86@kernel.org
> > Cc: linux-arch@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > 
> > Suggested-by: Catalin Marinas <catalin.marinas@arm.com>
> > Reviewed-by: Ingo Molnar <mingo@kernel.org>
> > Tested-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>	# s390
> > Tested-by: Christophe Leroy <christophe.leroy@c-s.fr>	# ppc32
> > Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> > Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
> > Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> > ---
> > This adds a test validation for architecture exported page table helpers.
> > Patch adds basic transformation tests at various levels of the page table.
> > 
> > This test was originally suggested by Catalin during arm64 THP migration
> > RFC discussion earlier. Going forward it can include more specific tests
> > with respect to various generic MM functions like THP, HugeTLB etc and
> > platform specific tests.
> > 
> > https://lore.kernel.org/linux-mm/20190628102003.GA56463@arrakis.emea.arm.com/
> > 
> > Needs to be applied on linux V5.6-rc2
> > 
> > Changes in V14:
> > 
> > - Disabled DEBUG_VM_PGFLAGS for IA64 and ARM (32 Bit) per Andrew and Christophe
> > - Updated DEBUG_VM_PGFLAGS documentation wrt EXPERT and disabled platforms
> > - Updated RANDOM_[OR|NZ]VALUE open encodings with GENMASK() per Catalin
> > - Updated s390 constraint bits from 12 to 4 (S390_MASK_BITS) per Gerald
> > - Updated in-code documentation for RANDOM_ORVALUE per Gerald
> > - Updated pxx_basic_tests() to use invert functions first per Catalin
> > - Dropped ARCH_HAS_4LEVEL_HACK check from pud_basic_tests()
> > - Replaced __ARCH_HAS_[4|5]LEVEL_HACK with __PAGETABLE_[PUD|P4D]_FOLDED per Catalin
> > - Trimmed the CC list on the commit message per Catalin
> > 
> > Changes in V13: (https://patchwork.kernel.org/project/linux-mm/list/?series=237125)
> > 
> > - Subscribed s390 platform and updated debug-vm-pgtable/arch-support.txt per Gerald
> > - Dropped keyword 'extern' from debug_vm_pgtable() declaration per Christophe
> > - Moved debug_vm_pgtable() declarations to <linux/mmdebug.h> per Christophe
> > - Moved debug_vm_pgtable() call site into kernel_init() per Christophe
> > - Changed CONFIG_DEBUG_VM_PGTABLE rules per Christophe
> > - Updated commit to include new supported platforms and changed config selection
> > 
> > Changes in V12: (https://patchwork.kernel.org/project/linux-mm/list/?series=233905)
> > 
> > - Replaced __mmdrop() with mmdrop()
> > - Enable ARCH_HAS_DEBUG_VM_PGTABLE on X86 for non CONFIG_X86_PAE platforms as the
> >   test procedure interfere with pre-allocated PMDs attached to the PGD resulting
> >   in runtime failures with VM_BUG_ON()
> > 
> > Changes in V11: (https://patchwork.kernel.org/project/linux-mm/list/?series=221135)
> > 
> > - Rebased the patch on V5.4
> > 
> > Changes in V10: (https://patchwork.kernel.org/project/linux-mm/list/?series=205529)
> > 
> > - Always enable DEBUG_VM_PGTABLE when DEBUG_VM is enabled per Ingo
> > - Added tags from Ingo
> > 
> > Changes in V9: (https://patchwork.kernel.org/project/linux-mm/list/?series=201429)
> > 
> > - Changed feature support enumeration for powerpc platforms per Christophe
> > - Changed config wrapper for basic_[pmd|pud]_tests() to enable ARC platform
> > - Enabled the test on ARC platform
> > 
> > Changes in V8: (https://patchwork.kernel.org/project/linux-mm/list/?series=194297)
> > 
> > - Enabled ARCH_HAS_DEBUG_VM_PGTABLE on PPC32 platform per Christophe
> > - Updated feature documentation as DEBUG_VM_PGTABLE is now enabled on PPC32 platform
> > - Moved ARCH_HAS_DEBUG_VM_PGTABLE earlier to indent it with DEBUG_VM per Christophe
> > - Added an information message in debug_vm_pgtable() per Christophe
> > - Dropped random_vaddr boundary condition checks per Christophe and Qian
> > - Replaced virt_addr_valid() check with pfn_valid() check in debug_vm_pgtable()
> > - Slightly changed pr_fmt(fmt) information
> > 
> > Changes in V7: (https://patchwork.kernel.org/project/linux-mm/list/?series=193051)
> > 
> > - Memory allocation and free routines for mapped pages have been droped
> > - Mapped pfns are derived from standard kernel text symbol per Matthew
> > - Moved debug_vm_pgtaable() after page_alloc_init_late() per Michal and Qian 
> > - Updated the commit message per Michal
> > - Updated W=1 GCC warning problem on x86 per Qian Cai
> > - Addition of new alloc_contig_pages() helper has been submitted separately
> > 
> > Changes in V6: (https://patchwork.kernel.org/project/linux-mm/list/?series=187589)
> > 
> > - Moved alloc_gigantic_page_order() into mm/page_alloc.c per Michal
> > - Moved alloc_gigantic_page_order() within CONFIG_CONTIG_ALLOC in the test
> > - Folded Andrew's include/asm-generic/pgtable.h fix into the test patch 2/2
> > 
> > Changes in V5: (https://patchwork.kernel.org/project/linux-mm/list/?series=185991)
> > 
> > - Redefined and moved X86 mm_p4d_folded() into a different header per Kirill/Ingo
> > - Updated the config option comment per Ingo and dropped 'kernel module' reference
> > - Updated the commit message and dropped 'kernel module' reference
> > - Changed DEBUG_ARCH_PGTABLE_TEST into DEBUG_VM_PGTABLE per Ingo
> > - Moved config option from mm/Kconfig.debug into lib/Kconfig.debug
> > - Renamed core test function arch_pgtable_tests() as debug_vm_pgtable()
> > - Renamed mm/arch_pgtable_test.c as mm/debug_vm_pgtable.c
> > - debug_vm_pgtable() gets called from kernel_init_freeable() after init_mm_internals()
> > - Added an entry in Documentation/features/debug/ per Ingo
> > - Enabled the test on arm64 and x86 platforms for now
> > 
> > Changes in V4: (https://patchwork.kernel.org/project/linux-mm/list/?series=183465)
> > 
> > - Disable DEBUG_ARCH_PGTABLE_TEST for ARM and IA64 platforms
> > 
> > Changes in V3: (https://lore.kernel.org/patchwork/project/lkml/list/?series=411216)
> > 
> > - Changed test trigger from module format into late_initcall()
> > - Marked all functions with __init to be freed after completion
> > - Changed all __PGTABLE_PXX_FOLDED checks as mm_pxx_folded()
> > - Folded in PPC32 fixes from Christophe
> > 
> > Changes in V2:
> > 
> > https://lore.kernel.org/linux-mm/1568268173-31302-1-git-send-email-anshuman.khandual@arm.com/T/#t
> > 
> > - Fixed small typo error in MODULE_DESCRIPTION()
> > - Fixed m64k build problems for lvalue concerns in pmd_xxx_tests()
> > - Fixed dynamic page table level folding problems on x86 as per Kirril
> > - Fixed second pointers during pxx_populate_tests() per Kirill and Gerald
> > - Allocate and free pte table with pte_alloc_one/pte_free per Kirill
> > - Modified pxx_clear_tests() to accommodate s390 lower 12 bits situation
> > - Changed RANDOM_NZVALUE value from 0xbe to 0xff
> > - Changed allocation, usage, free sequence for saved_ptep
> > - Renamed VMA_FLAGS as VMFLAGS
> > - Implemented a new method for random vaddr generation
> > - Implemented some other cleanups
> > - Dropped extern reference to mm_alloc()
> > - Created and exported new alloc_gigantic_page_order()
> > - Dropped the custom allocator and used new alloc_gigantic_page_order()
> > 
> > Changes in V1:
> > 
> > https://lore.kernel.org/linux-mm/1567497706-8649-1-git-send-email-anshuman.khandual@arm.com/
> > 
> > - Added fallback mechanism for PMD aligned memory allocation failure
> > 
> > Changes in RFC V2:
> > 
> > https://lore.kernel.org/linux-mm/1565335998-22553-1-git-send-email-anshuman.khandual@arm.com/T/#u
> > 
> > - Moved test module and it's config from lib/ to mm/
> > - Renamed config TEST_ARCH_PGTABLE as DEBUG_ARCH_PGTABLE_TEST
> > - Renamed file from test_arch_pgtable.c to arch_pgtable_test.c
> > - Added relevant MODULE_DESCRIPTION() and MODULE_AUTHOR() details
> > - Dropped loadable module config option
> > - Basic tests now use memory blocks with required size and alignment
> > - PUD aligned memory block gets allocated with alloc_contig_range()
> > - If PUD aligned memory could not be allocated it falls back on PMD aligned
> >   memory block from page allocator and pud_* tests are skipped
> > - Clear and populate tests now operate on real in memory page table entries
> > - Dummy mm_struct gets allocated with mm_alloc()
> > - Dummy page table entries get allocated with [pud|pmd|pte]_alloc_[map]()
> > - Simplified [p4d|pgd]_basic_tests(), now has random values in the entries
> > 
> > Original RFC V1:
> > 
> > https://lore.kernel.org/linux-mm/1564037723-26676-1-git-send-email-anshuman.khandual@arm.com/
> > 
> > 
> >  .../debug/debug-vm-pgtable/arch-support.txt   |  35 ++
> >  arch/arc/Kconfig                              |   1 +
> >  arch/arm64/Kconfig                            |   1 +
> >  arch/powerpc/Kconfig                          |   1 +
> >  arch/s390/Kconfig                             |   1 +
> >  arch/x86/Kconfig                              |   1 +
> >  arch/x86/include/asm/pgtable_64.h             |   6 +
> >  include/linux/mmdebug.h                       |   5 +
> >  init/main.c                                   |   2 +
> >  lib/Kconfig.debug                             |  26 ++
> >  mm/Makefile                                   |   1 +
> >  mm/debug_vm_pgtable.c                         | 389 ++++++++++++++++++
> >  12 files changed, 469 insertions(+)
> >  create mode 100644 Documentation/features/debug/debug-vm-pgtable/arch-support.txt
> >  create mode 100644 mm/debug_vm_pgtable.c
> > 
> > diff --git a/Documentation/features/debug/debug-vm-pgtable/arch-support.txt b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
> > new file mode 100644
> > index 000000000000..64d0f9b15c49
> > --- /dev/null
> > +++ b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
> > @@ -0,0 +1,35 @@
> > +#
> > +# Feature name:          debug-vm-pgtable
> > +#         Kconfig:       ARCH_HAS_DEBUG_VM_PGTABLE
> > +#         description:   arch supports pgtable tests for semantics compliance
> > +#
> > +    -----------------------
> > +    |         arch |status|
> > +    -----------------------
> > +    |       alpha: | TODO |
> > +    |         arc: |  ok  |
> > +    |         arm: | TODO |
> > +    |       arm64: |  ok  |
> > +    |         c6x: | TODO |
> > +    |        csky: | TODO |
> > +    |       h8300: | TODO |
> > +    |     hexagon: | TODO |
> > +    |        ia64: | TODO |
> > +    |        m68k: | TODO |
> > +    |  microblaze: | TODO |
> > +    |        mips: | TODO |
> > +    |       nds32: | TODO |
> > +    |       nios2: | TODO |
> > +    |    openrisc: | TODO |
> > +    |      parisc: | TODO |
> > +    |  powerpc/32: |  ok  |
> > +    |  powerpc/64: | TODO |
> > +    |       riscv: | TODO |
> > +    |        s390: |  ok  |
> > +    |          sh: | TODO |
> > +    |       sparc: | TODO |
> > +    |          um: | TODO |
> > +    |   unicore32: | TODO |
> > +    |         x86: |  ok  |
> > +    |      xtensa: | TODO |
> > +    -----------------------
> > diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
> > index ff2a393b635c..3e72e6cf0e42 100644
> > --- a/arch/arc/Kconfig
> > +++ b/arch/arc/Kconfig
> > @@ -6,6 +6,7 @@
> >  config ARC
> >  	def_bool y
> >  	select ARC_TIMERS
> > +	select ARCH_HAS_DEBUG_VM_PGTABLE
> >  	select ARCH_HAS_DMA_PREP_COHERENT
> >  	select ARCH_HAS_PTE_SPECIAL
> >  	select ARCH_HAS_SETUP_DMA_OPS
> > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> > index 0b30e884e088..aaf8ba415145 100644
> > --- a/arch/arm64/Kconfig
> > +++ b/arch/arm64/Kconfig
> > @@ -11,6 +11,7 @@ config ARM64
> >  	select ACPI_PPTT if ACPI
> >  	select ARCH_CLOCKSOURCE_DATA
> >  	select ARCH_HAS_DEBUG_VIRTUAL
> > +	select ARCH_HAS_DEBUG_VM_PGTABLE
> >  	select ARCH_HAS_DEVMEM_IS_ALLOWED
> >  	select ARCH_HAS_DMA_PREP_COHERENT
> >  	select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index 497b7d0b2d7e..8d5ae14c5d4c 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -116,6 +116,7 @@ config PPC
> >  	#
> >  	select ARCH_32BIT_OFF_T if PPC32
> >  	select ARCH_HAS_DEBUG_VIRTUAL
> > +	select ARCH_HAS_DEBUG_VM_PGTABLE if PPC32
> >  	select ARCH_HAS_DEVMEM_IS_ALLOWED
> >  	select ARCH_HAS_ELF_RANDOMIZE
> >  	select ARCH_HAS_FORTIFY_SOURCE
> > diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
> > index 8abe77536d9d..af284dbb07e7 100644
> > --- a/arch/s390/Kconfig
> > +++ b/arch/s390/Kconfig
> > @@ -59,6 +59,7 @@ config KASAN_SHADOW_OFFSET
> >  config S390
> >  	def_bool y
> >  	select ARCH_BINFMT_ELF_STATE
> > +	select ARCH_HAS_DEBUG_VM_PGTABLE
> >  	select ARCH_HAS_DEVMEM_IS_ALLOWED
> >  	select ARCH_HAS_ELF_RANDOMIZE
> >  	select ARCH_HAS_FORTIFY_SOURCE
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index beea77046f9b..df8a19e52e82 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -61,6 +61,7 @@ config X86
> >  	select ARCH_CLOCKSOURCE_INIT
> >  	select ARCH_HAS_ACPI_TABLE_UPGRADE	if ACPI
> >  	select ARCH_HAS_DEBUG_VIRTUAL
> > +	select ARCH_HAS_DEBUG_VM_PGTABLE	if !X86_PAE
> >  	select ARCH_HAS_DEVMEM_IS_ALLOWED
> >  	select ARCH_HAS_ELF_RANDOMIZE
> >  	select ARCH_HAS_FAST_MULTIPLIER
> > diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
> > index 0b6c4042942a..fb0e76d254b3 100644
> > --- a/arch/x86/include/asm/pgtable_64.h
> > +++ b/arch/x86/include/asm/pgtable_64.h
> > @@ -53,6 +53,12 @@ static inline void sync_initial_page_table(void) { }
> >  
> >  struct mm_struct;
> >  
> > +#define mm_p4d_folded mm_p4d_folded
> > +static inline bool mm_p4d_folded(struct mm_struct *mm)
> > +{
> > +	return !pgtable_l5_enabled();
> > +}
> > +
> >  void set_pte_vaddr_p4d(p4d_t *p4d_page, unsigned long vaddr, pte_t new_pte);
> >  void set_pte_vaddr_pud(pud_t *pud_page, unsigned long vaddr, pte_t new_pte);
> >  
> > diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
> > index 2ad72d2c8cc5..5339aa14b749 100644
> > --- a/include/linux/mmdebug.h
> > +++ b/include/linux/mmdebug.h
> > @@ -64,4 +64,9 @@ void dump_mm(const struct mm_struct *mm);
> >  #define VM_BUG_ON_PGFLAGS(cond, page) BUILD_BUG_ON_INVALID(cond)
> >  #endif
> >  
> > +#ifdef CONFIG_DEBUG_VM_PGTABLE
> > +void debug_vm_pgtable(void);
> > +#else
> > +static inline void debug_vm_pgtable(void) { }
> > +#endif
> >  #endif
> > diff --git a/init/main.c b/init/main.c
> > index cc0ee4873419..adf37e8b1d69 100644
> > --- a/init/main.c
> > +++ b/init/main.c
> > @@ -94,6 +94,7 @@
> >  #include <linux/rodata_test.h>
> >  #include <linux/jump_label.h>
> >  #include <linux/mem_encrypt.h>
> > +#include <linux/mmdebug.h>
> >  
> >  #include <asm/io.h>
> >  #include <asm/bugs.h>
> > @@ -1323,6 +1324,7 @@ static int __ref kernel_init(void *unused)
> >  	kernel_init_freeable();
> >  	/* need to finish all async __init code before freeing the memory */
> >  	async_synchronize_full();
> > +	debug_vm_pgtable();
> >  	ftrace_free_init_mem();
> >  	free_initmem();
> >  	mark_readonly();
> > diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
> > index 69def4a9df00..1b5bd9f7c967 100644
> > --- a/lib/Kconfig.debug
> > +++ b/lib/Kconfig.debug
> > @@ -653,6 +653,12 @@ config SCHED_STACK_END_CHECK
> >  	  data corruption or a sporadic crash at a later stage once the region
> >  	  is examined. The runtime overhead introduced is minimal.
> >  
> > +config ARCH_HAS_DEBUG_VM_PGTABLE
> > +	bool
> > +	help
> > +	  An architecture should select this when it can successfully
> > +	  build and run DEBUG_VM_PGTABLE.
> > +
> >  config DEBUG_VM
> >  	bool "Debug VM"
> >  	depends on DEBUG_KERNEL
> > @@ -688,6 +694,26 @@ config DEBUG_VM_PGFLAGS
> >  
> >  	  If unsure, say N.
> >  
> > +config DEBUG_VM_PGTABLE
> > +	bool "Debug arch page table for semantics compliance"
> > +	depends on MMU
> > +	depends on !IA64 && !ARM
> > +	depends on ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
> > +	default n if !ARCH_HAS_DEBUG_VM_PGTABLE
> > +	default y if DEBUG_VM
> > +	help
> > +	  This option provides a debug method which can be used to test
> > +	  architecture page table helper functions on various platforms in
> > +	  verifying if they comply with expected generic MM semantics. This
> > +	  will help architecture code in making sure that any changes or
> > +	  new additions of these helpers still conform to expected
> > +	  semantics of the generic MM. Platforms will have to opt in for
> > +	  this through ARCH_HAS_DEBUG_VM_PGTABLE. Although it can also be
> > +	  enabled through EXPERT without requiring code change. This test
> > +	  is disabled on IA64 and ARM platforms where it fails to build.
> > +
> > +	  If unsure, say N.
> > +
> >  config ARCH_HAS_DEBUG_VIRTUAL
> >  	bool
> >  
> > diff --git a/mm/Makefile b/mm/Makefile
> > index 272e66039e70..b0692e6a4b58 100644
> > --- a/mm/Makefile
> > +++ b/mm/Makefile
> > @@ -87,6 +87,7 @@ obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
> >  obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
> >  obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
> >  obj-$(CONFIG_DEBUG_RODATA_TEST) += rodata_test.o
> > +obj-$(CONFIG_DEBUG_VM_PGTABLE) += debug_vm_pgtable.o
> >  obj-$(CONFIG_PAGE_OWNER) += page_owner.o
> >  obj-$(CONFIG_CLEANCACHE) += cleancache.o
> >  obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
> > diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> > new file mode 100644
> > index 000000000000..70bf8ed8fd51
> > --- /dev/null
> > +++ b/mm/debug_vm_pgtable.c
> > @@ -0,0 +1,389 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * This kernel test validates architecture page table helpers and
> > + * accessors and helps in verifying their continued compliance with
> > + * expected generic MM semantics.
> > + *
> > + * Copyright (C) 2019 ARM Ltd.
> > + *
> > + * Author: Anshuman Khandual <anshuman.khandual@arm.com>
> > + */
> > +#define pr_fmt(fmt) "debug_vm_pgtable: %s: " fmt, __func__
> > +
> > +#include <linux/gfp.h>
> > +#include <linux/highmem.h>
> > +#include <linux/hugetlb.h>
> > +#include <linux/kernel.h>
> > +#include <linux/kconfig.h>
> > +#include <linux/mm.h>
> > +#include <linux/mman.h>
> > +#include <linux/mm_types.h>
> > +#include <linux/module.h>
> > +#include <linux/pfn_t.h>
> > +#include <linux/printk.h>
> > +#include <linux/random.h>
> > +#include <linux/spinlock.h>
> > +#include <linux/swap.h>
> > +#include <linux/swapops.h>
> > +#include <linux/start_kernel.h>
> > +#include <linux/sched/mm.h>
> > +#include <asm/pgalloc.h>
> > +#include <asm/pgtable.h>
> > +
> > +/*
> > + * Basic operations
> > + *
> > + * mkold(entry)			= An old and not a young entry
> > + * mkyoung(entry)		= A young and not an old entry
> > + * mkdirty(entry)		= A dirty and not a clean entry
> > + * mkclean(entry)		= A clean and not a dirty entry
> > + * mkwrite(entry)		= A write and not a write protected entry
> > + * wrprotect(entry)		= A write protected and not a write entry
> > + * pxx_bad(entry)		= A mapped and non-table entry
> > + * pxx_same(entry1, entry2)	= Both entries hold the exact same value
> > + */
> > +#define VMFLAGS	(VM_READ|VM_WRITE|VM_EXEC)
> > +
> > +/*
> > + * On s390 platform, the lower 4 bits are used to identify given page table
> > + * entry type. But these bits might affect the ability to clear entries with
> > + * pxx_clear() because of how dynamic page table folding works on s390. So
> > + * while loading up the entries do not change the lower 4 bits. It does not
> > + * have affect any other platform.
> > + */
> > +#define S390_MASK_BITS	4
> > +#define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
> > +#define RANDOM_NZVALUE	GENMASK(7, 0)
> > +
> > +static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
> > +{
> > +	pte_t pte = pfn_pte(pfn, prot);
> > +
> > +	WARN_ON(!pte_same(pte, pte));
> > +	WARN_ON(!pte_young(pte_mkyoung(pte_mkold(pte))));
> > +	WARN_ON(!pte_dirty(pte_mkdirty(pte_mkclean(pte))));
> > +	WARN_ON(!pte_write(pte_mkwrite(pte_wrprotect(pte))));
> > +	WARN_ON(pte_young(pte_mkold(pte_mkyoung(pte))));
> > +	WARN_ON(pte_dirty(pte_mkclean(pte_mkdirty(pte))));
> > +	WARN_ON(pte_write(pte_wrprotect(pte_mkwrite(pte))));
> > +}
> > +
> > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > +static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot)
> > +{
> > +	pmd_t pmd = pfn_pmd(pfn, prot);
> > +
> > +	WARN_ON(!pmd_same(pmd, pmd));
> > +	WARN_ON(!pmd_young(pmd_mkyoung(pmd_mkold(pmd))));
> > +	WARN_ON(!pmd_dirty(pmd_mkdirty(pmd_mkclean(pmd))));
> > +	WARN_ON(!pmd_write(pmd_mkwrite(pmd_wrprotect(pmd))));
> > +	WARN_ON(pmd_young(pmd_mkold(pmd_mkyoung(pmd))));
> > +	WARN_ON(pmd_dirty(pmd_mkclean(pmd_mkdirty(pmd))));
> > +	WARN_ON(pmd_write(pmd_wrprotect(pmd_mkwrite(pmd))));
> > +	/*
> > +	 * A huge page does not point to next level page table
> > +	 * entry. Hence this must qualify as pmd_bad().
> > +	 */
> > +	WARN_ON(!pmd_bad(pmd_mkhuge(pmd)));
> > +}
> > +
> > +#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
> > +static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot)
> > +{
> > +	pud_t pud = pfn_pud(pfn, prot);
> > +
> > +	WARN_ON(!pud_same(pud, pud));
> > +	WARN_ON(!pud_young(pud_mkyoung(pud_mkold(pud))));
> > +	WARN_ON(!pud_write(pud_mkwrite(pud_wrprotect(pud))));
> > +	WARN_ON(pud_write(pud_wrprotect(pud_mkwrite(pud))));
> > +	WARN_ON(pud_young(pud_mkold(pud_mkyoung(pud))));
> > +
> > +	if (mm_pmd_folded(mm))
> > +		return;
> > +
> > +	/*
> > +	 * A huge page does not point to next level page table
> > +	 * entry. Hence this must qualify as pud_bad().
> > +	 */
> > +	WARN_ON(!pud_bad(pud_mkhuge(pud)));
> > +}
> > +#else
> > +static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) { }
> > +#endif
> > +#else
> > +static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot) { }
> > +static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) { }
> > +#endif
> > +
> > +static void __init p4d_basic_tests(unsigned long pfn, pgprot_t prot)
> > +{
> > +	p4d_t p4d;
> > +
> > +	memset(&p4d, RANDOM_NZVALUE, sizeof(p4d_t));
> > +	WARN_ON(!p4d_same(p4d, p4d));
> > +}
> > +
> > +static void __init pgd_basic_tests(unsigned long pfn, pgprot_t prot)
> > +{
> > +	pgd_t pgd;
> > +
> > +	memset(&pgd, RANDOM_NZVALUE, sizeof(pgd_t));
> > +	WARN_ON(!pgd_same(pgd, pgd));
> > +}
> > +
> > +#ifndef __PAGETABLE_PUD_FOLDED
> > +static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp)
> > +{
> > +	pud_t pud = READ_ONCE(*pudp);
> > +
> > +	if (mm_pmd_folded(mm))
> > +		return;
> > +
> > +	pud = __pud(pud_val(pud) | RANDOM_ORVALUE);
> > +	WRITE_ONCE(*pudp, pud);
> > +	pud_clear(pudp);
> > +	pud = READ_ONCE(*pudp);
> > +	WARN_ON(!pud_none(pud));
> > +}
> > +
> > +static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
> > +				      pmd_t *pmdp)
> > +{
> > +	pud_t pud;
> > +
> > +	if (mm_pmd_folded(mm))
> > +		return;
> > +	/*
> > +	 * This entry points to next level page table page.
> > +	 * Hence this must not qualify as pud_bad().
> > +	 */
> > +	pmd_clear(pmdp);
> > +	pud_clear(pudp);
> > +	pud_populate(mm, pudp, pmdp);
> > +	pud = READ_ONCE(*pudp);
> > +	WARN_ON(pud_bad(pud));
> > +}
> > +#else
> > +static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp) { }
> > +static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
> > +				      pmd_t *pmdp)
> > +{
> > +}
> > +#endif
> > +
> > +#ifndef __PAGETABLE_P4D_FOLDED
> > +static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp)
> > +{
> > +	p4d_t p4d = READ_ONCE(*p4dp);
> > +
> > +	if (mm_pud_folded(mm))
> > +		return;
> > +
> > +	p4d = __p4d(p4d_val(p4d) | RANDOM_ORVALUE);
> > +	WRITE_ONCE(*p4dp, p4d);
> > +	p4d_clear(p4dp);
> > +	p4d = READ_ONCE(*p4dp);
> > +	WARN_ON(!p4d_none(p4d));
> > +}
> > +
> > +static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
> > +				      pud_t *pudp)
> > +{
> > +	p4d_t p4d;
> > +
> > +	if (mm_pud_folded(mm))
> > +		return;
> > +
> > +	/*
> > +	 * This entry points to next level page table page.
> > +	 * Hence this must not qualify as p4d_bad().
> > +	 */
> > +	pud_clear(pudp);
> > +	p4d_clear(p4dp);
> > +	p4d_populate(mm, p4dp, pudp);
> > +	p4d = READ_ONCE(*p4dp);
> > +	WARN_ON(p4d_bad(p4d));
> > +}
> > +
> > +static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp)
> > +{
> > +	pgd_t pgd = READ_ONCE(*pgdp);
> > +
> > +	if (mm_p4d_folded(mm))
> > +		return;
> > +
> > +	pgd = __pgd(pgd_val(pgd) | RANDOM_ORVALUE);
> > +	WRITE_ONCE(*pgdp, pgd);
> > +	pgd_clear(pgdp);
> > +	pgd = READ_ONCE(*pgdp);
> > +	WARN_ON(!pgd_none(pgd));
> > +}
> > +
> > +static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
> > +				      p4d_t *p4dp)
> > +{
> > +	pgd_t pgd;
> > +
> > +	if (mm_p4d_folded(mm))
> > +		return;
> > +
> > +	/*
> > +	 * This entry points to next level page table page.
> > +	 * Hence this must not qualify as pgd_bad().
> > +	 */
> > +	p4d_clear(p4dp);
> > +	pgd_clear(pgdp);
> > +	pgd_populate(mm, pgdp, p4dp);
> > +	pgd = READ_ONCE(*pgdp);
> > +	WARN_ON(pgd_bad(pgd));
> > +}
> > +#else
> > +static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp) { }
> > +static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp) { }
> > +static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
> > +				      pud_t *pudp)
> > +{
> > +}
> > +static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
> > +				      p4d_t *p4dp)
> > +{
> > +}
> > +#endif
> > +
> > +static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)
> > +{
> > +	pte_t pte = READ_ONCE(*ptep);
> > +
> > +	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
> > +	WRITE_ONCE(*ptep, pte);
> > +	pte_clear(mm, 0, ptep);
> > +	pte = READ_ONCE(*ptep);
> > +	WARN_ON(!pte_none(pte));
> > +}
> > +
> > +static void __init pmd_clear_tests(struct mm_struct *mm, pmd_t *pmdp)
> > +{
> > +	pmd_t pmd = READ_ONCE(*pmdp);
> > +
> > +	pmd = __pmd(pmd_val(pmd) | RANDOM_ORVALUE);
> > +	WRITE_ONCE(*pmdp, pmd);
> > +	pmd_clear(pmdp);
> > +	pmd = READ_ONCE(*pmdp);
> > +	WARN_ON(!pmd_none(pmd));
> > +}
> > +
> > +static void __init pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
> > +				      pgtable_t pgtable)
> > +{
> > +	pmd_t pmd;
> > +
> > +	/*
> > +	 * This entry points to next level page table page.
> > +	 * Hence this must not qualify as pmd_bad().
> > +	 */
> > +	pmd_clear(pmdp);
> > +	pmd_populate(mm, pmdp, pgtable);
> > +	pmd = READ_ONCE(*pmdp);
> > +	WARN_ON(pmd_bad(pmd));
> > +}
> > +
> > +static unsigned long __init get_random_vaddr(void)
> > +{
> > +	unsigned long random_vaddr, random_pages, total_user_pages;
> > +
> > +	total_user_pages = (TASK_SIZE - FIRST_USER_ADDRESS) / PAGE_SIZE;
> > +
> > +	random_pages = get_random_long() % total_user_pages;
> > +	random_vaddr = FIRST_USER_ADDRESS + random_pages * PAGE_SIZE;
> > +
> > +	return random_vaddr;
> > +}
> > +
> > +void __init debug_vm_pgtable(void)
> > +{
> > +	struct mm_struct *mm;
> > +	pgd_t *pgdp;
> > +	p4d_t *p4dp, *saved_p4dp;
> > +	pud_t *pudp, *saved_pudp;
> > +	pmd_t *pmdp, *saved_pmdp, pmd;
> > +	pte_t *ptep;
> > +	pgtable_t saved_ptep;
> > +	pgprot_t prot;
> > +	phys_addr_t paddr;
> > +	unsigned long vaddr, pte_aligned, pmd_aligned;
> > +	unsigned long pud_aligned, p4d_aligned, pgd_aligned;
> > +
> > +	pr_info("Validating architecture page table helpers\n");
> > +	prot = vm_get_page_prot(VMFLAGS);
> > +	vaddr = get_random_vaddr();
> > +	mm = mm_alloc();
> > +	if (!mm) {
> > +		pr_err("mm_struct allocation failed\n");
> > +		return;
> > +	}
> > +
> > +	/*
> > +	 * PFN for mapping at PTE level is determined from a standard kernel
> > +	 * text symbol. But pfns for higher page table levels are derived by
> > +	 * masking lower bits of this real pfn. These derived pfns might not
> > +	 * exist on the platform but that does not really matter as pfn_pxx()
> > +	 * helpers will still create appropriate entries for the test. This
> > +	 * helps avoid large memory block allocations to be used for mapping
> > +	 * at higher page table levels.
> > +	 */
> > +	paddr = __pa(&start_kernel);
> > +
> > +	pte_aligned = (paddr & PAGE_MASK) >> PAGE_SHIFT;
> > +	pmd_aligned = (paddr & PMD_MASK) >> PAGE_SHIFT;
> > +	pud_aligned = (paddr & PUD_MASK) >> PAGE_SHIFT;
> > +	p4d_aligned = (paddr & P4D_MASK) >> PAGE_SHIFT;
> > +	pgd_aligned = (paddr & PGDIR_MASK) >> PAGE_SHIFT;
> > +	WARN_ON(!pfn_valid(pte_aligned));
> > +
> > +	pgdp = pgd_offset(mm, vaddr);
> > +	p4dp = p4d_alloc(mm, pgdp, vaddr);
> > +	pudp = pud_alloc(mm, p4dp, vaddr);
> > +	pmdp = pmd_alloc(mm, pudp, vaddr);
> > +	ptep = pte_alloc_map(mm, pmdp, vaddr);
> > +
> > +	/*
> > +	 * Save all the page table page addresses as the page table
> > +	 * entries will be used for testing with random or garbage
> > +	 * values. These saved addresses will be used for freeing
> > +	 * page table pages.
> > +	 */
> > +	pmd = READ_ONCE(*pmdp);
> > +	saved_p4dp = p4d_offset(pgdp, 0UL);
> > +	saved_pudp = pud_offset(p4dp, 0UL);
> > +	saved_pmdp = pmd_offset(pudp, 0UL);
> > +	saved_ptep = pmd_pgtable(pmd);
> > +
> > +	pte_basic_tests(pte_aligned, prot);
> > +	pmd_basic_tests(pmd_aligned, prot);
> > +	pud_basic_tests(pud_aligned, prot);
> > +	p4d_basic_tests(p4d_aligned, prot);
> > +	pgd_basic_tests(pgd_aligned, prot);
> > +
> > +	pte_clear_tests(mm, ptep);
> > +	pmd_clear_tests(mm, pmdp);
> > +	pud_clear_tests(mm, pudp);
> > +	p4d_clear_tests(mm, p4dp);
> > +	pgd_clear_tests(mm, pgdp);
> > +
> > +	pte_unmap(ptep);
> > +
> > +	pmd_populate_tests(mm, pmdp, saved_ptep);
> > +	pud_populate_tests(mm, pudp, saved_pmdp);
> > +	p4d_populate_tests(mm, p4dp, saved_pudp);
> > +	pgd_populate_tests(mm, pgdp, saved_p4dp);
> > +
> > +	p4d_free(mm, saved_p4dp);
> > +	pud_free(mm, saved_pudp);
> > +	pmd_free(mm, saved_pmdp);
> > +	pte_free(mm, saved_ptep);
> > +
> > +	mm_dec_nr_puds(mm);
> > +	mm_dec_nr_pmds(mm);
> > +	mm_dec_nr_ptes(mm);
> > +	mmdrop(mm);
> > +}
Christophe Leroy Feb. 26, 2020, 2:44 p.m. UTC | #4
Le 26/02/2020 à 15:12, Qian Cai a écrit :
> On Wed, 2020-02-26 at 09:09 -0500, Qian Cai wrote:
>> On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
>>
>> How useful is this that straightly crash the powerpc?
> 
> And then generate warnings on arm64,
> 
> [  146.634626][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
> architecture page table helpers
> [  146.643995][    T1] ------------[ cut here ]------------
> [  146.649350][    T1] virt_to_phys used for non-linear address:
> (____ptrval____) (start_kernel+0x0/0x580)

Must be something wrong with the following in debug_vm_pgtable()

	paddr = __pa(&start_kernel);

Is there any explaination why start_kernel() is not in linear memory on 
ARM64 ?

Christophe
Christophe Leroy Feb. 26, 2020, 2:45 p.m. UTC | #5
Le 26/02/2020 à 15:09, Qian Cai a écrit :
> On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
>> This adds tests which will validate architecture page table helpers and
>> other accessors in their compliance with expected generic MM semantics.
>> This will help various architectures in validating changes to existing
>> page table helpers or addition of new ones.
>>
>> This test covers basic page table entry transformations including but not
>> limited to old, young, dirty, clean, write, write protect etc at various
>> level along with populating intermediate entries with next page table page
>> and validating them.
>>
>> Test page table pages are allocated from system memory with required size
>> and alignments. The mapped pfns at page table levels are derived from a
>> real pfn representing a valid kernel text symbol. This test gets called
>> inside kernel_init() right after async_synchronize_full().
>>
>> This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any
>> architecture, which is willing to subscribe this test will need to select
>> ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390
>> and ppc32 platforms where the test is known to build and run successfully.
>> Going forward, other architectures too can subscribe the test after fixing
>> any build or runtime problems with their page table helpers. Meanwhile for
>> better platform coverage, the test can also be enabled with CONFIG_EXPERT
>> even without ARCH_HAS_DEBUG_VM_PGTABLE.
>>
>> Folks interested in making sure that a given platform's page table helpers
>> conform to expected generic MM semantics should enable the above config
>> which will just trigger this test during boot. Any non conformity here will
>> be reported as an warning which would need to be fixed. This test will help
>> catch any changes to the agreed upon semantics expected from generic MM and
>> enable platforms to accommodate it thereafter.
> 
> How useful is this that straightly crash the powerpc?
> 
> [   23.263425][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
> architecture page table helpers
> [   23.263625][    T1] ------------[ cut here ]------------
> [   23.263649][    T1] kernel BUG at arch/powerpc/mm/pgtable.c:274!

The problem on PPC64 is known and has to be investigated and fixed.

Christophe
Qian Cai Feb. 26, 2020, 3:51 p.m. UTC | #6
On Wed, 2020-02-26 at 15:45 +0100, Christophe Leroy wrote:
> 
> Le 26/02/2020 à 15:09, Qian Cai a écrit :
> > On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
> > > This adds tests which will validate architecture page table helpers and
> > > other accessors in their compliance with expected generic MM semantics.
> > > This will help various architectures in validating changes to existing
> > > page table helpers or addition of new ones.
> > > 
> > > This test covers basic page table entry transformations including but not
> > > limited to old, young, dirty, clean, write, write protect etc at various
> > > level along with populating intermediate entries with next page table page
> > > and validating them.
> > > 
> > > Test page table pages are allocated from system memory with required size
> > > and alignments. The mapped pfns at page table levels are derived from a
> > > real pfn representing a valid kernel text symbol. This test gets called
> > > inside kernel_init() right after async_synchronize_full().
> > > 
> > > This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any
> > > architecture, which is willing to subscribe this test will need to select
> > > ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390
> > > and ppc32 platforms where the test is known to build and run successfully.
> > > Going forward, other architectures too can subscribe the test after fixing
> > > any build or runtime problems with their page table helpers. Meanwhile for
> > > better platform coverage, the test can also be enabled with CONFIG_EXPERT
> > > even without ARCH_HAS_DEBUG_VM_PGTABLE.
> > > 
> > > Folks interested in making sure that a given platform's page table helpers
> > > conform to expected generic MM semantics should enable the above config
> > > which will just trigger this test during boot. Any non conformity here will
> > > be reported as an warning which would need to be fixed. This test will help
> > > catch any changes to the agreed upon semantics expected from generic MM and
> > > enable platforms to accommodate it thereafter.
> > 
> > How useful is this that straightly crash the powerpc?
> > 
> > [   23.263425][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
> > architecture page table helpers
> > [   23.263625][    T1] ------------[ cut here ]------------
> > [   23.263649][    T1] kernel BUG at arch/powerpc/mm/pgtable.c:274!
> 
> The problem on PPC64 is known and has to be investigated and fixed.

It might be interesting to hear what powerpc64 maintainers would say about it
and if it is actually worth "fixing" in the arch code, but that BUG_ON() was
there since 2009 and had not been exposed until this patch comes alone?
Anshuman Khandual Feb. 27, 2020, 2:34 a.m. UTC | #7
On 02/26/2020 08:14 PM, Christophe Leroy wrote:
> 
> 
> Le 26/02/2020 à 15:12, Qian Cai a écrit :
>> On Wed, 2020-02-26 at 09:09 -0500, Qian Cai wrote:
>>> On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
>>>
>>> How useful is this that straightly crash the powerpc?
>>
>> And then generate warnings on arm64,
>>
>> [  146.634626][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
>> architecture page table helpers
>> [  146.643995][    T1] ------------[ cut here ]------------
>> [  146.649350][    T1] virt_to_phys used for non-linear address:
>> (____ptrval____) (start_kernel+0x0/0x580)
> 
> Must be something wrong with the following in debug_vm_pgtable()
> 
>     paddr = __pa(&start_kernel);
> 
> Is there any explaination why start_kernel() is not in linear memory on ARM64 ?


Cc: + James Morse <james.morse@arm.com>

This warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol
i.e 'start_kernel' which might be outside the linear map. This happens due to
kernel mapping position randomization with KASLR. Adding James here in case he
might like to add more.

__pa_symbol() should have been used instead, for accessing the physical address
here. On arm64 __pa() does check for linear address with __is_lm_address() and
switch accordingly if it is a kernel text symbol. Nevertheless, its much better
to use __pa_symbol() here rather than __pa().

Rather than respining the patch once more, will just send a fix replacing this
helper __pa() with __pa_symbol() for Andrew to pick up as this patch is already
part of linux-next (next-20200226). But can definitely respin if that will be
preferred.

Thanks Qian for catching this.

> 
> Christophe
>
Andrew Morton Feb. 27, 2020, 4:03 a.m. UTC | #8
On Thu, 27 Feb 2020 08:04:05 +0530 Anshuman Khandual <anshuman.khandual@arm.com> wrote:

> > Must be something wrong with the following in debug_vm_pgtable()
> > 
> >     paddr = __pa(&start_kernel);
> > 
> > Is there any explaination why start_kernel() is not in linear memory on ARM64 ?
> 
> 
> Cc: + James Morse <james.morse@arm.com>
> 
> This warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol
> i.e 'start_kernel' which might be outside the linear map. This happens due to
> kernel mapping position randomization with KASLR. Adding James here in case he
> might like to add more.
> 
> __pa_symbol() should have been used instead, for accessing the physical address
> here. On arm64 __pa() does check for linear address with __is_lm_address() and
> switch accordingly if it is a kernel text symbol. Nevertheless, its much better
> to use __pa_symbol() here rather than __pa().
> 
> Rather than respining the patch once more, will just send a fix replacing this
> helper __pa() with __pa_symbol() for Andrew to pick up as this patch is already
> part of linux-next (next-20200226). But can definitely respin if that will be
> preferred.

I didn't see this fix?  I assume it's this?  If so, are we sure it's OK to be
added to -next without testing??



From: Andrew Morton <akpm@linux-foundation.org>
Subject: mm-debug-add-tests-validating-architecture-page-table-helpers-fix

A warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol
i.e 'start_kernel' which might be outside the linear map.  This happens
due to kernel mapping position randomization with KASLR.

__pa_symbol() should have been used instead, for accessing the physical
address here.  On arm64 __pa() does check for linear address with
__is_lm_address() and switch accordingly if it is a kernel text symbol. 
Nevertheless, its much better to use __pa_symbol() here rather than
__pa().

Reported-by: Qian Cai <cai@lca.pw>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: James Morse <james.morse@arm.com>
Cc: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/debug_vm_pgtable.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/debug_vm_pgtable.c~mm-debug-add-tests-validating-architecture-page-table-helpers-fix
+++ a/mm/debug_vm_pgtable.c
@@ -331,7 +331,7 @@ void __init debug_vm_pgtable(void)
 	 * helps avoid large memory block allocations to be used for mapping
 	 * at higher page table levels.
 	 */
-	paddr = __pa(&start_kernel);
+	paddr = __pa_symbol(&start_kernel);
 
 	pte_aligned = (paddr & PAGE_MASK) >> PAGE_SHIFT;
 	pmd_aligned = (paddr & PMD_MASK) >> PAGE_SHIFT;
Anshuman Khandual Feb. 27, 2020, 4:07 a.m. UTC | #9
On 02/27/2020 09:33 AM, Andrew Morton wrote:
> On Thu, 27 Feb 2020 08:04:05 +0530 Anshuman Khandual <anshuman.khandual@arm.com> wrote:
> 
>>> Must be something wrong with the following in debug_vm_pgtable()
>>>
>>>     paddr = __pa(&start_kernel);
>>>
>>> Is there any explaination why start_kernel() is not in linear memory on ARM64 ?
>>
>>
>> Cc: + James Morse <james.morse@arm.com>
>>
>> This warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol
>> i.e 'start_kernel' which might be outside the linear map. This happens due to
>> kernel mapping position randomization with KASLR. Adding James here in case he
>> might like to add more.
>>
>> __pa_symbol() should have been used instead, for accessing the physical address
>> here. On arm64 __pa() does check for linear address with __is_lm_address() and
>> switch accordingly if it is a kernel text symbol. Nevertheless, its much better
>> to use __pa_symbol() here rather than __pa().
>>
>> Rather than respining the patch once more, will just send a fix replacing this
>> helper __pa() with __pa_symbol() for Andrew to pick up as this patch is already
>> part of linux-next (next-20200226). But can definitely respin if that will be
>> preferred.
> 
> I didn't see this fix?  I assume it's this?  If so, are we sure it's OK to be
> added to -next without testing??

My patch just missed your response here within a minute :) Please consider this.
It has been tested on x86 and arm64.

https://patchwork.kernel.org/patch/11407715/

> 
> 
> 
> From: Andrew Morton <akpm@linux-foundation.org>
> Subject: mm-debug-add-tests-validating-architecture-page-table-helpers-fix
> 
> A warning gets exposed with DEBUG_VIRTUAL due to __pa() on a kernel symbol
> i.e 'start_kernel' which might be outside the linear map.  This happens
> due to kernel mapping position randomization with KASLR.
> 
> __pa_symbol() should have been used instead, for accessing the physical
> address here.  On arm64 __pa() does check for linear address with
> __is_lm_address() and switch accordingly if it is a kernel text symbol. 
> Nevertheless, its much better to use __pa_symbol() here rather than
> __pa().
> 
> Reported-by: Qian Cai <cai@lca.pw>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Christophe Leroy <christophe.leroy@c-s.fr>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  mm/debug_vm_pgtable.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> --- a/mm/debug_vm_pgtable.c~mm-debug-add-tests-validating-architecture-page-table-helpers-fix
> +++ a/mm/debug_vm_pgtable.c
> @@ -331,7 +331,7 @@ void __init debug_vm_pgtable(void)
>  	 * helps avoid large memory block allocations to be used for mapping
>  	 * at higher page table levels.
>  	 */
> -	paddr = __pa(&start_kernel);
> +	paddr = __pa_symbol(&start_kernel);
>  
>  	pte_aligned = (paddr & PAGE_MASK) >> PAGE_SHIFT;
>  	pmd_aligned = (paddr & PMD_MASK) >> PAGE_SHIFT;
> _
> 
>
Qian Cai March 2, 2020, 7:40 p.m. UTC | #10
On Wed, 2020-02-26 at 10:51 -0500, Qian Cai wrote:
> On Wed, 2020-02-26 at 15:45 +0100, Christophe Leroy wrote:
> > 
> > Le 26/02/2020 à 15:09, Qian Cai a écrit :
> > > On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
> > > > This adds tests which will validate architecture page table helpers and
> > > > other accessors in their compliance with expected generic MM semantics.
> > > > This will help various architectures in validating changes to existing
> > > > page table helpers or addition of new ones.
> > > > 
> > > > This test covers basic page table entry transformations including but not
> > > > limited to old, young, dirty, clean, write, write protect etc at various
> > > > level along with populating intermediate entries with next page table page
> > > > and validating them.
> > > > 
> > > > Test page table pages are allocated from system memory with required size
> > > > and alignments. The mapped pfns at page table levels are derived from a
> > > > real pfn representing a valid kernel text symbol. This test gets called
> > > > inside kernel_init() right after async_synchronize_full().
> > > > 
> > > > This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any
> > > > architecture, which is willing to subscribe this test will need to select
> > > > ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390
> > > > and ppc32 platforms where the test is known to build and run successfully.
> > > > Going forward, other architectures too can subscribe the test after fixing
> > > > any build or runtime problems with their page table helpers. Meanwhile for
> > > > better platform coverage, the test can also be enabled with CONFIG_EXPERT
> > > > even without ARCH_HAS_DEBUG_VM_PGTABLE.
> > > > 
> > > > Folks interested in making sure that a given platform's page table helpers
> > > > conform to expected generic MM semantics should enable the above config
> > > > which will just trigger this test during boot. Any non conformity here will
> > > > be reported as an warning which would need to be fixed. This test will help
> > > > catch any changes to the agreed upon semantics expected from generic MM and
> > > > enable platforms to accommodate it thereafter.
> > > 
> > > How useful is this that straightly crash the powerpc?
> > > 
> > > [   23.263425][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
> > > architecture page table helpers
> > > [   23.263625][    T1] ------------[ cut here ]------------
> > > [   23.263649][    T1] kernel BUG at arch/powerpc/mm/pgtable.c:274!
> > 
> > The problem on PPC64 is known and has to be investigated and fixed.
> 
> It might be interesting to hear what powerpc64 maintainers would say about it
> and if it is actually worth "fixing" in the arch code, but that BUG_ON() was
> there since 2009 and had not been exposed until this patch comes alone?

This patch below makes it works on powerpc64 in order to dodge the BUG_ON()s in 
assert_pte_locked() triggered by pte_clear_tests().


diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 96dd7d574cef..50b385233971 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -55,6 +55,8 @@
 #define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
 #define RANDOM_NZVALUE	GENMASK(7, 0)
 
+unsigned long vaddr;
+
 static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
 {
 	pte_t pte = pfn_pte(pfn, prot);
@@ -256,7 +258,7 @@ static void __init pte_clear_tests(struct mm_struct *mm,
pte_t *ptep)
 
 	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
 	WRITE_ONCE(*ptep, pte);
-	pte_clear(mm, 0, ptep);
+	pte_clear(mm, vaddr, ptep);
 	pte = READ_ONCE(*ptep);
 	WARN_ON(!pte_none(pte));
 }
@@ -310,8 +312,9 @@ void __init debug_vm_pgtable(void)
 	pgtable_t saved_ptep;
 	pgprot_t prot;
 	phys_addr_t paddr;
-	unsigned long vaddr, pte_aligned, pmd_aligned;
+	unsigned long pte_aligned, pmd_aligned;
 	unsigned long pud_aligned, p4d_aligned, pgd_aligned;
+	spinlock_t *ptl;
 
 	pr_info("Validating architecture page table helpers\n");
 	prot = vm_get_page_prot(VMFLAGS);
@@ -344,7 +347,7 @@ void __init debug_vm_pgtable(void)
 	p4dp = p4d_alloc(mm, pgdp, vaddr);
 	pudp = pud_alloc(mm, p4dp, vaddr);
 	pmdp = pmd_alloc(mm, pudp, vaddr);
-	ptep = pte_alloc_map(mm, pmdp, vaddr);
+	ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
 
 	/*
 	 * Save all the page table page addresses as the page table
@@ -370,7 +373,7 @@ void __init debug_vm_pgtable(void)
 	p4d_clear_tests(mm, p4dp);
 	pgd_clear_tests(mm, pgdp);
 
-	pte_unmap(ptep);
+	pte_unmap_unlock(ptep, ptl);
 
 	pmd_populate_tests(mm, pmdp, saved_ptep);
 	pud_populate_tests(mm, pudp, saved_pmdp);
Anshuman Khandual March 3, 2020, 5:55 a.m. UTC | #11
On 03/03/2020 01:10 AM, Qian Cai wrote:
> On Wed, 2020-02-26 at 10:51 -0500, Qian Cai wrote:
>> On Wed, 2020-02-26 at 15:45 +0100, Christophe Leroy wrote:
>>>
>>> Le 26/02/2020 à 15:09, Qian Cai a écrit :
>>>> On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
>>>>> This adds tests which will validate architecture page table helpers and
>>>>> other accessors in their compliance with expected generic MM semantics.
>>>>> This will help various architectures in validating changes to existing
>>>>> page table helpers or addition of new ones.
>>>>>
>>>>> This test covers basic page table entry transformations including but not
>>>>> limited to old, young, dirty, clean, write, write protect etc at various
>>>>> level along with populating intermediate entries with next page table page
>>>>> and validating them.
>>>>>
>>>>> Test page table pages are allocated from system memory with required size
>>>>> and alignments. The mapped pfns at page table levels are derived from a
>>>>> real pfn representing a valid kernel text symbol. This test gets called
>>>>> inside kernel_init() right after async_synchronize_full().
>>>>>
>>>>> This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any
>>>>> architecture, which is willing to subscribe this test will need to select
>>>>> ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390
>>>>> and ppc32 platforms where the test is known to build and run successfully.
>>>>> Going forward, other architectures too can subscribe the test after fixing
>>>>> any build or runtime problems with their page table helpers. Meanwhile for
>>>>> better platform coverage, the test can also be enabled with CONFIG_EXPERT
>>>>> even without ARCH_HAS_DEBUG_VM_PGTABLE.
>>>>>
>>>>> Folks interested in making sure that a given platform's page table helpers
>>>>> conform to expected generic MM semantics should enable the above config
>>>>> which will just trigger this test during boot. Any non conformity here will
>>>>> be reported as an warning which would need to be fixed. This test will help
>>>>> catch any changes to the agreed upon semantics expected from generic MM and
>>>>> enable platforms to accommodate it thereafter.
>>>>
>>>> How useful is this that straightly crash the powerpc?
>>>>
>>>> [   23.263425][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
>>>> architecture page table helpers
>>>> [   23.263625][    T1] ------------[ cut here ]------------
>>>> [   23.263649][    T1] kernel BUG at arch/powerpc/mm/pgtable.c:274!
>>>
>>> The problem on PPC64 is known and has to be investigated and fixed.
>>
>> It might be interesting to hear what powerpc64 maintainers would say about it
>> and if it is actually worth "fixing" in the arch code, but that BUG_ON() was
>> there since 2009 and had not been exposed until this patch comes alone?
> 
> This patch below makes it works on powerpc64 in order to dodge the BUG_ON()s in 
> assert_pte_locked() triggered by pte_clear_tests().
> 
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 96dd7d574cef..50b385233971 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -55,6 +55,8 @@
>  #define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
>  #define RANDOM_NZVALUE	GENMASK(7, 0)
>  
> +unsigned long vaddr;
> +
>  static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
>  {
>  	pte_t pte = pfn_pte(pfn, prot);
> @@ -256,7 +258,7 @@ static void __init pte_clear_tests(struct mm_struct *mm,
> pte_t *ptep)
>  
>  	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>  	WRITE_ONCE(*ptep, pte);
> -	pte_clear(mm, 0, ptep);
> +	pte_clear(mm, vaddr, ptep);
>  	pte = READ_ONCE(*ptep);
>  	WARN_ON(!pte_none(pte));
>  }
> @@ -310,8 +312,9 @@ void __init debug_vm_pgtable(void)
>  	pgtable_t saved_ptep;
>  	pgprot_t prot;
>  	phys_addr_t paddr;
> -	unsigned long vaddr, pte_aligned, pmd_aligned;
> +	unsigned long pte_aligned, pmd_aligned;
>  	unsigned long pud_aligned, p4d_aligned, pgd_aligned;
> +	spinlock_t *ptl;
>  
>  	pr_info("Validating architecture page table helpers\n");
>  	prot = vm_get_page_prot(VMFLAGS);
> @@ -344,7 +347,7 @@ void __init debug_vm_pgtable(void)
>  	p4dp = p4d_alloc(mm, pgdp, vaddr);
>  	pudp = pud_alloc(mm, p4dp, vaddr);
>  	pmdp = pmd_alloc(mm, pudp, vaddr);
> -	ptep = pte_alloc_map(mm, pmdp, vaddr);
> +	ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>  
>  	/*
>  	 * Save all the page table page addresses as the page table
> @@ -370,7 +373,7 @@ void __init debug_vm_pgtable(void)
>  	p4d_clear_tests(mm, p4dp);
>  	pgd_clear_tests(mm, pgdp);
>  
> -	pte_unmap(ptep);
> +	pte_unmap_unlock(ptep, ptl);
>  
>  	pmd_populate_tests(mm, pmdp, saved_ptep);
>  	pud_populate_tests(mm, pudp, saved_pmdp);
> 

Below is slightly modified version of your change above and should still
prevent the bug on powerpc. Will it be possible for you to re-test this
? Once confirmed, will send a patch enabling this test on powerpc64
keeping your authorship. Thank you.

 mm/debug_vm_pgtable.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 96dd7d574cef..c310f52c2b80 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -250,13 +250,14 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
 }
 #endif

-static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)
+static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
+                                  unsigned long vaddr)
 {
        pte_t pte = READ_ONCE(*ptep);

        pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
        WRITE_ONCE(*ptep, pte);
-       pte_clear(mm, 0, ptep);
+       pte_clear(mm, vaddr, ptep);
        pte = READ_ONCE(*ptep);
        WARN_ON(!pte_none(pte));
 }
@@ -302,6 +303,7 @@ static unsigned long __init get_random_vaddr(void)
 void __init debug_vm_pgtable(void)
 {
        struct mm_struct *mm;
+       spinlock_t *uninitialized_var(ptl);
        pgd_t *pgdp;
        p4d_t *p4dp, *saved_p4dp;
        pud_t *pudp, *saved_pudp;
@@ -344,7 +346,7 @@ void __init debug_vm_pgtable(void)
        p4dp = p4d_alloc(mm, pgdp, vaddr);
        pudp = pud_alloc(mm, p4dp, vaddr);
        pmdp = pmd_alloc(mm, pudp, vaddr);
-       ptep = pte_alloc_map(mm, pmdp, vaddr);
+       ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);

        /*
         * Save all the page table page addresses as the page table
@@ -364,13 +366,13 @@ void __init debug_vm_pgtable(void)
        p4d_basic_tests(p4d_aligned, prot);
        pgd_basic_tests(pgd_aligned, prot);

-       pte_clear_tests(mm, ptep);
+       pte_clear_tests(mm, ptep, vaddr);
        pmd_clear_tests(mm, pmdp);
        pud_clear_tests(mm, pudp);
        p4d_clear_tests(mm, p4dp);
        pgd_clear_tests(mm, pgdp);

-       pte_unmap(ptep);
+       pte_unmap_unlock(ptep, ptl);

        pmd_populate_tests(mm, pmdp, saved_ptep);
        pud_populate_tests(mm, pudp, saved_pmdp);
Christophe Leroy March 3, 2020, 5:59 a.m. UTC | #12
Le 02/03/2020 à 20:40, Qian Cai a écrit :
> On Wed, 2020-02-26 at 10:51 -0500, Qian Cai wrote:
>> On Wed, 2020-02-26 at 15:45 +0100, Christophe Leroy wrote:
>>>
>>> Le 26/02/2020 à 15:09, Qian Cai a écrit :
>>>> On Mon, 2020-02-17 at 08:47 +0530, Anshuman Khandual wrote:
>>>>> This adds tests which will validate architecture page table helpers and
>>>>> other accessors in their compliance with expected generic MM semantics.
>>>>> This will help various architectures in validating changes to existing
>>>>> page table helpers or addition of new ones.
>>>>>
>>>>> This test covers basic page table entry transformations including but not
>>>>> limited to old, young, dirty, clean, write, write protect etc at various
>>>>> level along with populating intermediate entries with next page table page
>>>>> and validating them.
>>>>>
>>>>> Test page table pages are allocated from system memory with required size
>>>>> and alignments. The mapped pfns at page table levels are derived from a
>>>>> real pfn representing a valid kernel text symbol. This test gets called
>>>>> inside kernel_init() right after async_synchronize_full().
>>>>>
>>>>> This test gets built and run when CONFIG_DEBUG_VM_PGTABLE is selected. Any
>>>>> architecture, which is willing to subscribe this test will need to select
>>>>> ARCH_HAS_DEBUG_VM_PGTABLE. For now this is limited to arc, arm64, x86, s390
>>>>> and ppc32 platforms where the test is known to build and run successfully.
>>>>> Going forward, other architectures too can subscribe the test after fixing
>>>>> any build or runtime problems with their page table helpers. Meanwhile for
>>>>> better platform coverage, the test can also be enabled with CONFIG_EXPERT
>>>>> even without ARCH_HAS_DEBUG_VM_PGTABLE.
>>>>>
>>>>> Folks interested in making sure that a given platform's page table helpers
>>>>> conform to expected generic MM semantics should enable the above config
>>>>> which will just trigger this test during boot. Any non conformity here will
>>>>> be reported as an warning which would need to be fixed. This test will help
>>>>> catch any changes to the agreed upon semantics expected from generic MM and
>>>>> enable platforms to accommodate it thereafter.
>>>>
>>>> How useful is this that straightly crash the powerpc?
>>>>
>>>> [   23.263425][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
>>>> architecture page table helpers
>>>> [   23.263625][    T1] ------------[ cut here ]------------
>>>> [   23.263649][    T1] kernel BUG at arch/powerpc/mm/pgtable.c:274!
>>>
>>> The problem on PPC64 is known and has to be investigated and fixed.
>>
>> It might be interesting to hear what powerpc64 maintainers would say about it
>> and if it is actually worth "fixing" in the arch code, but that BUG_ON() was
>> there since 2009 and had not been exposed until this patch comes alone?
> 
> This patch below makes it works on powerpc64 in order to dodge the BUG_ON()s in
> assert_pte_locked() triggered by pte_clear_tests().
> 
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 96dd7d574cef..50b385233971 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -55,6 +55,8 @@
>   #define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
>   #define RANDOM_NZVALUE	GENMASK(7, 0)
>   
> +unsigned long vaddr;
> +

Can we avoid global var ?

>   static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
>   {
>   	pte_t pte = pfn_pte(pfn, prot);
> @@ -256,7 +258,7 @@ static void __init pte_clear_tests(struct mm_struct *mm,
> pte_t *ptep)
>   
>   	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>   	WRITE_ONCE(*ptep, pte);
> -	pte_clear(mm, 0, ptep);
> +	pte_clear(mm, vaddr, ptep);
>   	pte = READ_ONCE(*ptep);
>   	WARN_ON(!pte_none(pte));
>   }
> @@ -310,8 +312,9 @@ void __init debug_vm_pgtable(void)
>   	pgtable_t saved_ptep;
>   	pgprot_t prot;
>   	phys_addr_t paddr;
> -	unsigned long vaddr, pte_aligned, pmd_aligned;

Can we pass local vaddr to pte_clear_tests() instead of making it a 
global var ?

> +	unsigned long pte_aligned, pmd_aligned;
>   	unsigned long pud_aligned, p4d_aligned, pgd_aligned;
> +	spinlock_t *ptl;
>   
>   	pr_info("Validating architecture page table helpers\n");
>   	prot = vm_get_page_prot(VMFLAGS);
> @@ -344,7 +347,7 @@ void __init debug_vm_pgtable(void)
>   	p4dp = p4d_alloc(mm, pgdp, vaddr);
>   	pudp = pud_alloc(mm, p4dp, vaddr);
>   	pmdp = pmd_alloc(mm, pudp, vaddr);
> -	ptep = pte_alloc_map(mm, pmdp, vaddr);
> +	ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
>   
>   	/*
>   	 * Save all the page table page addresses as the page table
> @@ -370,7 +373,7 @@ void __init debug_vm_pgtable(void)
>   	p4d_clear_tests(mm, p4dp);
>   	pgd_clear_tests(mm, pgdp);
>   
> -	pte_unmap(ptep);
> +	pte_unmap_unlock(ptep, ptl);
>   
>   	pmd_populate_tests(mm, pmdp, saved_ptep);
>   	pud_populate_tests(mm, pudp, saved_pmdp);
> 

Christophe
Qian Cai March 4, 2020, 1:39 a.m. UTC | #13
> Below is slightly modified version of your change above and should still
> prevent the bug on powerpc. Will it be possible for you to re-test this
> ? Once confirmed, will send a patch enabling this test on powerpc64
> keeping your authorship. Thank you.

This works fine on radix MMU but I decided to go a bit future to test hash
MMU. The kernel will stuck here below. I did confirm that pte_alloc_map_lock()
was successful, so I don’t understand hash MMU well enough to tell why
it could still take an interrupt at pte_clear_tests() even before we calls
pte_unmap_unlock()?

[   33.881515][    T1] ok 8 - property-entry
[   33.883653][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
architecture page table helpers
[   60.418885][    C8] watchdog: BUG: soft lockup - CPU#8 stuck for 23s!
[swapper/0:1]
[   60.418913][    C8] Modules linked in:
[   60.418927][    C8] irq event stamp: 2896762
[   60.418945][    C8] hardirqs last  enabled at (2896761): [<c00000000000dec8>]
fast_exc_return_irq+0x28/0x34
[   60.418960][    C8] hardirqs last disabled at (2896762): [<c00000000000924c>]
decrementer_common+0x10c/0x130
[   60.418985][    C8] softirqs last  enabled at (2896760): [<c0000000009a1bf0>]
__do_softirq+0x640/0x8c8
[   60.419009][    C8] softirqs last disabled at (2896753): [<c000000000113cbc>]
irq_exit+0x16c/0x1d0
[   60.419024][    C8] CPU: 8 PID: 1 Comm: swapper/0 Not tainted 5.6.0-rc4-next-
20200303+ #7
[   60.419055][    C8] NIP:  c00000000103dc14 LR: c00000000103db0c CTR:
0000000000000000
[   60.419076][    C8] REGS: c00000003dd4fa30 TRAP: 0901   Not tainted  (5.6.0-
rc4-next-20200303+)
[   60.419107][    C8] MSR:  9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR:
42000222  XER: 00000000
[   60.419134][    C8] CFAR: c00000000103dc1c IRQMASK: 0 
[   60.419134][    C8] GPR00: c00000000103db0c c00000003dd4fcc0 c000000001657d00
05210001000000c0 
[   60.419134][    C8] GPR04: 8000000000000105 000000000000000a 00000000f4d9864c
0000000000000001 
[   60.419134][    C8] GPR08: 0000000000000000 ffffffffffffffff 0000000000000001
00000000000a0000 
[   60.419134][    C8] GPR12: 0000000000000000 c000001fffff9880 
[   60.419220][    C8] NIP [c00000000103dc14] debug_vm_pgtable+0x7a8/0xbb4
hash__pte_update at arch/powerpc/include/asm/book3s/64/hash.h:159
(inlined by) pte_update at arch/powerpc/include/asm/book3s/64/pgtable.h:359
(inlined by) pte_clear at arch/powerpc/include/asm/book3s/64/pgtable.h:477
(inlined by) pte_clear_tests at mm/debug_vm_pgtable.c:259
(inlined by) debug_vm_pgtable at mm/debug_vm_pgtable.c:368
[   60.419241][    C8] LR [c00000000103db0c] debug_vm_pgtable+0x6a0/0xbb4
pmd_basic_tests at mm/debug_vm_pgtable.c:74
(inlined by) debug_vm_pgtable at mm/debug_vm_pgtable.c:363
[   60.419260][    C8] Call Trace:
[   60.419278][    C8] [c00000003dd4fcc0] [c00000000103d994]
debug_vm_pgtable+0x528/0xbb4 (unreliable)
[   60.419302][    C8] [c00000003dd4fdb0] [c000000000010eac]
kernel_init+0x30/0x194
[   60.419325][    C8] [c00000003dd4fe20] [c00000000000b748]
ret_from_kernel_thread+0x5c/0x74
[   60.419363][    C8] Instruction dump:
[   60.419382][    C8] 7d075078 7ce74b78 7ce0f9ad 40c2fff0 7e449378 7fc3f378
4b03531d 60000000 
[   60.419416][    C8] 48000080 3920ffff 39400001 39000000 <7e00f8a8> 7e075039
40c2fff8 7e074878 
[   98.908889][    C8] rcu: INFO: rcu_sched self-detected stall on CPU
[   98.908933][    C8] rcu:         8-....: (6500 ticks this GP)
idle=522/1/0x4000000000000002 softirq=132/132 fqs=3250 
[   98.908963][    C8]         (t=6501 jiffies g=-719 q=510)
[   98.908984][    C8] NMI backtrace for cpu 8
[   98.909012][    C8] CPU: 8 PID: 1 Comm: swapper/0 Tainted:
G             L    5.6.0-rc4-next-20200303+ #7
[   98.909025][    C8] Call Trace:
[   98.909046][    C8] [c00000003dd4f360] [c000000000970fe0]
dump_stack+0xf4/0x164 (unreliable)
[   98.909070][    C8] [c00000003dd4f3b0] [c00000000097dcf4]
nmi_cpu_backtrace+0x1b4/0x1e0
[   98.909084][    C8] [c00000003dd4f450] [c00000000097df48]
nmi_trigger_cpumask_backtrace+0x228/0x2c0
[   98.909118][    C8] [c00000003dd4f500] [c000000000057bf8]
arch_trigger_cpumask_backtrace+0x28/0x40
[   98.909152][    C8] [c00000003dd4f520] [c000000000202dd4]
rcu_dump_cpu_stacks+0x1c4/0x234
[   98.909184][    C8] [c00000003dd4f5a0] [c000000000201634]
rcu_sched_clock_irq+0xd54/0x1130
[   98.909207][    C8] [c00000003dd4f6c0] [c000000000217068]
update_process_times+0x48/0xb0
[   98.909239][    C8] [c00000003dd4f6f0] [c0000000002358b4]
tick_sched_handle+0x34/0xb0
[   98.909262][    C8] [c00000003dd4f720] [c0000000002361d8]
tick_sched_timer+0x68/0xe0
[   98.909284][    C8] [c00000003dd4f760] [c000000000219768]
__hrtimer_run_queues+0x528/0xa60
[   98.909306][    C8] [c00000003dd4f880] [c00000000021ab58]
hrtimer_interrupt+0x128/0x330
[   98.909329][    C8] [c00000003dd4f930] [c00000000002e1b4]
timer_interrupt+0x264/0x680
[   98.909352][    C8] [c00000003dd4f9c0] [c000000000009264]
decrementer_common+0x124/0x130
[   98.909366][    C8] --- interrupt: 901 at debug_vm_pgtable+0x7a8/0xbb4
[   98.909366][    C8]     LR = debug_vm_pgtable+0x6a0/0xbb4
[   98.909402][    C8] [c00000003dd4fcc0] [c00000000103d994]
debug_vm_pgtable+0x528/0xbb4 (unreliable)
[   98.909435][    C8] [c00000003dd4fdb0] [c000000000010eac]
kernel_init+0x30/0x194
[   98.909467][    C8] [c00000003dd4fe20] [c00000000000b748]
ret_from_kernel_thread+0x5c/0x74
[  124.418885][    C8] watchdog: BUG: soft lockup - CPU#8 stuck for 22s!
[swapper/0:1]
[  124.418914][    C8] Modules linked in:
[  124.418926][    C8] irq event stamp: 2937938
[  124.418940][    C8] hardirqs last  enabled at (2937937): [<c00000000000dec8>]
fast_exc_return_irq+0x28/0x34
[  124.418964][    C8] hardirqs last disabled at (2937938): [<c00000000000924c>]
decrementer_common+0x10c/0x130
[  124.418980][    C8] softirqs last  enabled at (2937936): [<c0000000009a1bf0>]
__do_softirq+0x640/0x8c8
[  124.419013][    C8] softirqs last disabled at (2937929): [<c000000000113cbc>]
irq_exit+0x16c/0x1d0
[  124.419036][    C8] CPU: 8 PID: 1 Comm: swapper/0 Tainted:
G             L    5.6.0-rc4-next-20200303+ #7
[  124.419059][    C8] NIP:  c00000000103dc14 LR: c00000000103db0c CTR:
0000000000000000
[  124.419080][    C8] REGS: c00000003dd4fa30 TRAP: 0901   Tainted:
G             L     (5.6.0-rc4-next-20200303+)
[  124.419103][    C8] MSR:  9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE>  CR:
42000222  XER: 00000000
[  124.419121][    C8] CFAR: c00000000103dc1c IRQMASK: 0 
[  124.419121][    C8] GPR00: c00000000103db0c c00000003dd4fcc0 c000000001657d00
05210001000000c0 
[  124.419121][    C8] GPR04: 8000000000000105 000000000000000a 00000000f4d9864c
0000000000000001 
[  124.419121][    C8] GPR08: 0000000000000000 ffffffffffffffff 0000000000000001
00000000000a0000 
[  124.419121][    C8] GPR12: 0000000000000000 c000001fffff9880 
[  124.419234][    C8] NIP [c00000000103dc14] debug_vm_pgtable+0x7a8/0xbb4
[  124.419254][    C8] LR [c00000000103db0c] debug_vm_pgtable+0x6a0/0xbb4
[  124.419274][    C8] Call Trace:
[  124.419291][    C8] [c00000003dd4fcc0] [c00000000103d994]
debug_vm_pgtable+0x528/0xbb4 (unreliable)
[  124.419324][    C8] [c00000003dd4fdb0] [c000000000010eac]
kernel_init+0x30/0x194
[  124.419347][    C8] [c00000003dd4fe20] [c00000000000b748]
ret_from_kernel_thread+0x5c/0x74
[  124.419359][    C8] Instruction dump:
[  124.419378][    C8] 7d075078 7ce74b78 7ce0f9ad 40c2fff0 7e449378 7fc3f378
4b03531d 60000000 
[  124.419412][    C8] 48000080 3920ffff 39400001 39000000 <7e00f8a8> 7e075039
40c2fff8 7e074878

> 
> mm/debug_vm_pgtable.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
> index 96dd7d574cef..c310f52c2b80 100644
> --- a/mm/debug_vm_pgtable.c
> +++ b/mm/debug_vm_pgtable.c
> @@ -250,13 +250,14 @@ static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
> }
> #endif
> 
> -static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)
> +static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep,
> +                                  unsigned long vaddr)
> {
>        pte_t pte = READ_ONCE(*ptep);
> 
>        pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
>        WRITE_ONCE(*ptep, pte);
> -       pte_clear(mm, 0, ptep);
> +       pte_clear(mm, vaddr, ptep);
>        pte = READ_ONCE(*ptep);
>        WARN_ON(!pte_none(pte));
> }
> @@ -302,6 +303,7 @@ static unsigned long __init get_random_vaddr(void)
> void __init debug_vm_pgtable(void)
> {
>        struct mm_struct *mm;
> +       spinlock_t *uninitialized_var(ptl);
>        pgd_t *pgdp;
>        p4d_t *p4dp, *saved_p4dp;
>        pud_t *pudp, *saved_pudp;
> @@ -344,7 +346,7 @@ void __init debug_vm_pgtable(void)
>        p4dp = p4d_alloc(mm, pgdp, vaddr);
>        pudp = pud_alloc(mm, p4dp, vaddr);
>        pmdp = pmd_alloc(mm, pudp, vaddr);
> -       ptep = pte_alloc_map(mm, pmdp, vaddr);
> +       ptep = pte_alloc_map_lock(mm, pmdp, vaddr, &ptl);
> 
>        /*
>         * Save all the page table page addresses as the page table
> @@ -364,13 +366,13 @@ void __init debug_vm_pgtable(void)
>        p4d_basic_tests(p4d_aligned, prot);
>        pgd_basic_tests(pgd_aligned, prot);
> 
> -       pte_clear_tests(mm, ptep);
> +       pte_clear_tests(mm, ptep, vaddr);
>        pmd_clear_tests(mm, pmdp);
>        pud_clear_tests(mm, pudp);
>        p4d_clear_tests(mm, p4dp);
>        pgd_clear_tests(mm, pgdp);
> 
> -       pte_unmap(ptep);
> +       pte_unmap_unlock(ptep, ptl);
> 
>        pmd_populate_tests(mm, pmdp, saved_ptep);
>        pud_populate_tests(mm, pudp, saved_pmdp);
> -- 
> 2.20.1
Christophe Leroy March 4, 2020, 6:48 a.m. UTC | #14
Le 04/03/2020 à 02:39, Qian Cai a écrit :
> 
>> Below is slightly modified version of your change above and should still
>> prevent the bug on powerpc. Will it be possible for you to re-test this
>> ? Once confirmed, will send a patch enabling this test on powerpc64
>> keeping your authorship. Thank you.
> 
> This works fine on radix MMU but I decided to go a bit future to test hash
> MMU. The kernel will stuck here below. I did confirm that pte_alloc_map_lock()
> was successful, so I don’t understand hash MMU well enough to tell why
> it could still take an interrupt at pte_clear_tests() even before we calls
> pte_unmap_unlock()?

AFAIU, you are not taking an interrupt here. You are stuck in the 
pte_update(), most likely due to nested locks. Try with LOCKDEP ?

Christophe

> 
> [   33.881515][    T1] ok 8 - property-entry
> [   33.883653][    T1] debug_vm_pgtable: debug_vm_pgtable: Validating
> architecture page table helpers
> [   60.418885][    C8] watchdog: BUG: soft lockup - CPU#8 stuck for 23s!
> [swapper/0:1]
Qian Cai March 4, 2020, 11:29 a.m. UTC | #15
> On Mar 4, 2020, at 1:49 AM, Christophe Leroy <christophe.leroy@c-s.fr> wrote:
> 
> AFAIU, you are not taking an interrupt here. You are stuck in the pte_update(), most likely due to nested locks. Try with LOCKDEP ?

Not exactly sure what did you mean here, but the kernel has all lockdep enabled and did not flag anything here.
Anshuman Khandual March 5, 2020, 12:54 a.m. UTC | #16
On 03/04/2020 04:59 PM, Qian Cai wrote:
> 
> 
>> On Mar 4, 2020, at 1:49 AM, Christophe Leroy <christophe.leroy@c-s.fr> wrote:
>>
>> AFAIU, you are not taking an interrupt here. You are stuck in the pte_update(), most likely due to nested locks. Try with LOCKDEP ?
> 
> Not exactly sure what did you mean here, but the kernel has all lockdep enabled and did not flag anything here.

As the patch has been dropped from Linux next (next-20200304) perhaps in
order to fold back the __pa_symbol() fix [1], so I am planning to respin
the original patch once more as V15 while adding Qian's signed off by for
the powerpc part. For now lets enable radix MMU ppc64 along with existing
ppc32. As PPC_RADIX_MMU depends on PPC_BOOK3S_64, the following change
should be good enough ?

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 497b7d0b2d7e..8d5ae14c5d4c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -116,6 +116,7 @@  config PPC
 	#
 	select ARCH_32BIT_OFF_T if PPC32
 	select ARCH_HAS_DEBUG_VIRTUAL
+	select ARCH_HAS_DEBUG_VM_PGTABLE if (PPC_RADIX_MMU || PPC32)
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FORTIFY_SOURCE

[1] https://patchwork.kernel.org/patch/11407715/
Christophe Leroy March 5, 2020, 5:43 a.m. UTC | #17
Le 05/03/2020 à 01:54, Anshuman Khandual a écrit :
> 
> 
> On 03/04/2020 04:59 PM, Qian Cai wrote:
>>
>>
>>> On Mar 4, 2020, at 1:49 AM, Christophe Leroy <christophe.leroy@c-s.fr> wrote:
>>>
>>> AFAIU, you are not taking an interrupt here. You are stuck in the pte_update(), most likely due to nested locks. Try with LOCKDEP ?
>>
>> Not exactly sure what did you mean here, but the kernel has all lockdep enabled and did not flag anything here.
> 
> As the patch has been dropped from Linux next (next-20200304) perhaps in
> order to fold back the __pa_symbol() fix [1], so I am planning to respin
> the original patch once more as V15 while adding Qian's signed off by for
> the powerpc part. For now lets enable radix MMU ppc64 along with existing
> ppc32. As PPC_RADIX_MMU depends on PPC_BOOK3S_64, the following change
> should be good enough ?

I don't think so, even if you have the Radix MMU compiled in, hash MMU 
is used when Radix is not available or disabled. So until the Hash MMU 
problem is fixed, you cannot enable it by default.

Christophe
Anshuman Khandual March 5, 2020, 6:23 a.m. UTC | #18
On 03/05/2020 11:13 AM, Christophe Leroy wrote:
> 
> 
> Le 05/03/2020 à 01:54, Anshuman Khandual a écrit :
>>
>>
>> On 03/04/2020 04:59 PM, Qian Cai wrote:
>>>
>>>
>>>> On Mar 4, 2020, at 1:49 AM, Christophe Leroy <christophe.leroy@c-s.fr> wrote:
>>>>
>>>> AFAIU, you are not taking an interrupt here. You are stuck in the pte_update(), most likely due to nested locks. Try with LOCKDEP ?
>>>
>>> Not exactly sure what did you mean here, but the kernel has all lockdep enabled and did not flag anything here.
>>
>> As the patch has been dropped from Linux next (next-20200304) perhaps in
>> order to fold back the __pa_symbol() fix [1], so I am planning to respin
>> the original patch once more as V15 while adding Qian's signed off by for
>> the powerpc part. For now lets enable radix MMU ppc64 along with existing
>> ppc32. As PPC_RADIX_MMU depends on PPC_BOOK3S_64, the following change
>> should be good enough ?
> 
> I don't think so, even if you have the Radix MMU compiled in, hash MMU is used when Radix is not available or disabled. So until the Hash MMU problem is fixed, you cannot enable it by default.

So this implies, that with DEBUG_VM given kernel compiled with Radix MMU will
get stuck in soft lock up when forced to use hash MMU in cases where Radix MMU
is either not available or is disabled. Hence, we cannot enable that.

I will still fold the changes from Qian without enabling ppc64 Radix MMU and
respin V15. These new changes dont hurt, build every where and works good
on arm64 and x86 platforms. More over we know that they also fix a problem
for ppc64 Radix MMU platforms. Hence unless there are some other concerns we
should fold them in.

> 
> Christophe
>

Patch
diff mbox series

diff --git a/Documentation/features/debug/debug-vm-pgtable/arch-support.txt b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
new file mode 100644
index 000000000000..64d0f9b15c49
--- /dev/null
+++ b/Documentation/features/debug/debug-vm-pgtable/arch-support.txt
@@ -0,0 +1,35 @@ 
+#
+# Feature name:          debug-vm-pgtable
+#         Kconfig:       ARCH_HAS_DEBUG_VM_PGTABLE
+#         description:   arch supports pgtable tests for semantics compliance
+#
+    -----------------------
+    |         arch |status|
+    -----------------------
+    |       alpha: | TODO |
+    |         arc: |  ok  |
+    |         arm: | TODO |
+    |       arm64: |  ok  |
+    |         c6x: | TODO |
+    |        csky: | TODO |
+    |       h8300: | TODO |
+    |     hexagon: | TODO |
+    |        ia64: | TODO |
+    |        m68k: | TODO |
+    |  microblaze: | TODO |
+    |        mips: | TODO |
+    |       nds32: | TODO |
+    |       nios2: | TODO |
+    |    openrisc: | TODO |
+    |      parisc: | TODO |
+    |  powerpc/32: |  ok  |
+    |  powerpc/64: | TODO |
+    |       riscv: | TODO |
+    |        s390: |  ok  |
+    |          sh: | TODO |
+    |       sparc: | TODO |
+    |          um: | TODO |
+    |   unicore32: | TODO |
+    |         x86: |  ok  |
+    |      xtensa: | TODO |
+    -----------------------
diff --git a/arch/arc/Kconfig b/arch/arc/Kconfig
index ff2a393b635c..3e72e6cf0e42 100644
--- a/arch/arc/Kconfig
+++ b/arch/arc/Kconfig
@@ -6,6 +6,7 @@ 
 config ARC
 	def_bool y
 	select ARC_TIMERS
+	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DMA_PREP_COHERENT
 	select ARCH_HAS_PTE_SPECIAL
 	select ARCH_HAS_SETUP_DMA_OPS
diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 0b30e884e088..aaf8ba415145 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -11,6 +11,7 @@  config ARM64
 	select ACPI_PPTT if ACPI
 	select ARCH_CLOCKSOURCE_DATA
 	select ARCH_HAS_DEBUG_VIRTUAL
+	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_DMA_PREP_COHERENT
 	select ARCH_HAS_ACPI_TABLE_UPGRADE if ACPI
diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 497b7d0b2d7e..8d5ae14c5d4c 100644
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -116,6 +116,7 @@  config PPC
 	#
 	select ARCH_32BIT_OFF_T if PPC32
 	select ARCH_HAS_DEBUG_VIRTUAL
+	select ARCH_HAS_DEBUG_VM_PGTABLE if PPC32
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FORTIFY_SOURCE
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 8abe77536d9d..af284dbb07e7 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -59,6 +59,7 @@  config KASAN_SHADOW_OFFSET
 config S390
 	def_bool y
 	select ARCH_BINFMT_ELF_STATE
+	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FORTIFY_SOURCE
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index beea77046f9b..df8a19e52e82 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -61,6 +61,7 @@  config X86
 	select ARCH_CLOCKSOURCE_INIT
 	select ARCH_HAS_ACPI_TABLE_UPGRADE	if ACPI
 	select ARCH_HAS_DEBUG_VIRTUAL
+	select ARCH_HAS_DEBUG_VM_PGTABLE	if !X86_PAE
 	select ARCH_HAS_DEVMEM_IS_ALLOWED
 	select ARCH_HAS_ELF_RANDOMIZE
 	select ARCH_HAS_FAST_MULTIPLIER
diff --git a/arch/x86/include/asm/pgtable_64.h b/arch/x86/include/asm/pgtable_64.h
index 0b6c4042942a..fb0e76d254b3 100644
--- a/arch/x86/include/asm/pgtable_64.h
+++ b/arch/x86/include/asm/pgtable_64.h
@@ -53,6 +53,12 @@  static inline void sync_initial_page_table(void) { }
 
 struct mm_struct;
 
+#define mm_p4d_folded mm_p4d_folded
+static inline bool mm_p4d_folded(struct mm_struct *mm)
+{
+	return !pgtable_l5_enabled();
+}
+
 void set_pte_vaddr_p4d(p4d_t *p4d_page, unsigned long vaddr, pte_t new_pte);
 void set_pte_vaddr_pud(pud_t *pud_page, unsigned long vaddr, pte_t new_pte);
 
diff --git a/include/linux/mmdebug.h b/include/linux/mmdebug.h
index 2ad72d2c8cc5..5339aa14b749 100644
--- a/include/linux/mmdebug.h
+++ b/include/linux/mmdebug.h
@@ -64,4 +64,9 @@  void dump_mm(const struct mm_struct *mm);
 #define VM_BUG_ON_PGFLAGS(cond, page) BUILD_BUG_ON_INVALID(cond)
 #endif
 
+#ifdef CONFIG_DEBUG_VM_PGTABLE
+void debug_vm_pgtable(void);
+#else
+static inline void debug_vm_pgtable(void) { }
+#endif
 #endif
diff --git a/init/main.c b/init/main.c
index cc0ee4873419..adf37e8b1d69 100644
--- a/init/main.c
+++ b/init/main.c
@@ -94,6 +94,7 @@ 
 #include <linux/rodata_test.h>
 #include <linux/jump_label.h>
 #include <linux/mem_encrypt.h>
+#include <linux/mmdebug.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -1323,6 +1324,7 @@  static int __ref kernel_init(void *unused)
 	kernel_init_freeable();
 	/* need to finish all async __init code before freeing the memory */
 	async_synchronize_full();
+	debug_vm_pgtable();
 	ftrace_free_init_mem();
 	free_initmem();
 	mark_readonly();
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 69def4a9df00..1b5bd9f7c967 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -653,6 +653,12 @@  config SCHED_STACK_END_CHECK
 	  data corruption or a sporadic crash at a later stage once the region
 	  is examined. The runtime overhead introduced is minimal.
 
+config ARCH_HAS_DEBUG_VM_PGTABLE
+	bool
+	help
+	  An architecture should select this when it can successfully
+	  build and run DEBUG_VM_PGTABLE.
+
 config DEBUG_VM
 	bool "Debug VM"
 	depends on DEBUG_KERNEL
@@ -688,6 +694,26 @@  config DEBUG_VM_PGFLAGS
 
 	  If unsure, say N.
 
+config DEBUG_VM_PGTABLE
+	bool "Debug arch page table for semantics compliance"
+	depends on MMU
+	depends on !IA64 && !ARM
+	depends on ARCH_HAS_DEBUG_VM_PGTABLE || EXPERT
+	default n if !ARCH_HAS_DEBUG_VM_PGTABLE
+	default y if DEBUG_VM
+	help
+	  This option provides a debug method which can be used to test
+	  architecture page table helper functions on various platforms in
+	  verifying if they comply with expected generic MM semantics. This
+	  will help architecture code in making sure that any changes or
+	  new additions of these helpers still conform to expected
+	  semantics of the generic MM. Platforms will have to opt in for
+	  this through ARCH_HAS_DEBUG_VM_PGTABLE. Although it can also be
+	  enabled through EXPERT without requiring code change. This test
+	  is disabled on IA64 and ARM platforms where it fails to build.
+
+	  If unsure, say N.
+
 config ARCH_HAS_DEBUG_VIRTUAL
 	bool
 
diff --git a/mm/Makefile b/mm/Makefile
index 272e66039e70..b0692e6a4b58 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -87,6 +87,7 @@  obj-$(CONFIG_HWPOISON_INJECT) += hwpoison-inject.o
 obj-$(CONFIG_DEBUG_KMEMLEAK) += kmemleak.o
 obj-$(CONFIG_DEBUG_KMEMLEAK_TEST) += kmemleak-test.o
 obj-$(CONFIG_DEBUG_RODATA_TEST) += rodata_test.o
+obj-$(CONFIG_DEBUG_VM_PGTABLE) += debug_vm_pgtable.o
 obj-$(CONFIG_PAGE_OWNER) += page_owner.o
 obj-$(CONFIG_CLEANCACHE) += cleancache.o
 obj-$(CONFIG_MEMORY_ISOLATION) += page_isolation.o
diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
new file mode 100644
index 000000000000..70bf8ed8fd51
--- /dev/null
+++ b/mm/debug_vm_pgtable.c
@@ -0,0 +1,389 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * This kernel test validates architecture page table helpers and
+ * accessors and helps in verifying their continued compliance with
+ * expected generic MM semantics.
+ *
+ * Copyright (C) 2019 ARM Ltd.
+ *
+ * Author: Anshuman Khandual <anshuman.khandual@arm.com>
+ */
+#define pr_fmt(fmt) "debug_vm_pgtable: %s: " fmt, __func__
+
+#include <linux/gfp.h>
+#include <linux/highmem.h>
+#include <linux/hugetlb.h>
+#include <linux/kernel.h>
+#include <linux/kconfig.h>
+#include <linux/mm.h>
+#include <linux/mman.h>
+#include <linux/mm_types.h>
+#include <linux/module.h>
+#include <linux/pfn_t.h>
+#include <linux/printk.h>
+#include <linux/random.h>
+#include <linux/spinlock.h>
+#include <linux/swap.h>
+#include <linux/swapops.h>
+#include <linux/start_kernel.h>
+#include <linux/sched/mm.h>
+#include <asm/pgalloc.h>
+#include <asm/pgtable.h>
+
+/*
+ * Basic operations
+ *
+ * mkold(entry)			= An old and not a young entry
+ * mkyoung(entry)		= A young and not an old entry
+ * mkdirty(entry)		= A dirty and not a clean entry
+ * mkclean(entry)		= A clean and not a dirty entry
+ * mkwrite(entry)		= A write and not a write protected entry
+ * wrprotect(entry)		= A write protected and not a write entry
+ * pxx_bad(entry)		= A mapped and non-table entry
+ * pxx_same(entry1, entry2)	= Both entries hold the exact same value
+ */
+#define VMFLAGS	(VM_READ|VM_WRITE|VM_EXEC)
+
+/*
+ * On s390 platform, the lower 4 bits are used to identify given page table
+ * entry type. But these bits might affect the ability to clear entries with
+ * pxx_clear() because of how dynamic page table folding works on s390. So
+ * while loading up the entries do not change the lower 4 bits. It does not
+ * have affect any other platform.
+ */
+#define S390_MASK_BITS	4
+#define RANDOM_ORVALUE	GENMASK(BITS_PER_LONG - 1, S390_MASK_BITS)
+#define RANDOM_NZVALUE	GENMASK(7, 0)
+
+static void __init pte_basic_tests(unsigned long pfn, pgprot_t prot)
+{
+	pte_t pte = pfn_pte(pfn, prot);
+
+	WARN_ON(!pte_same(pte, pte));
+	WARN_ON(!pte_young(pte_mkyoung(pte_mkold(pte))));
+	WARN_ON(!pte_dirty(pte_mkdirty(pte_mkclean(pte))));
+	WARN_ON(!pte_write(pte_mkwrite(pte_wrprotect(pte))));
+	WARN_ON(pte_young(pte_mkold(pte_mkyoung(pte))));
+	WARN_ON(pte_dirty(pte_mkclean(pte_mkdirty(pte))));
+	WARN_ON(pte_write(pte_wrprotect(pte_mkwrite(pte))));
+}
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot)
+{
+	pmd_t pmd = pfn_pmd(pfn, prot);
+
+	WARN_ON(!pmd_same(pmd, pmd));
+	WARN_ON(!pmd_young(pmd_mkyoung(pmd_mkold(pmd))));
+	WARN_ON(!pmd_dirty(pmd_mkdirty(pmd_mkclean(pmd))));
+	WARN_ON(!pmd_write(pmd_mkwrite(pmd_wrprotect(pmd))));
+	WARN_ON(pmd_young(pmd_mkold(pmd_mkyoung(pmd))));
+	WARN_ON(pmd_dirty(pmd_mkclean(pmd_mkdirty(pmd))));
+	WARN_ON(pmd_write(pmd_wrprotect(pmd_mkwrite(pmd))));
+	/*
+	 * A huge page does not point to next level page table
+	 * entry. Hence this must qualify as pmd_bad().
+	 */
+	WARN_ON(!pmd_bad(pmd_mkhuge(pmd)));
+}
+
+#ifdef CONFIG_HAVE_ARCH_TRANSPARENT_HUGEPAGE_PUD
+static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot)
+{
+	pud_t pud = pfn_pud(pfn, prot);
+
+	WARN_ON(!pud_same(pud, pud));
+	WARN_ON(!pud_young(pud_mkyoung(pud_mkold(pud))));
+	WARN_ON(!pud_write(pud_mkwrite(pud_wrprotect(pud))));
+	WARN_ON(pud_write(pud_wrprotect(pud_mkwrite(pud))));
+	WARN_ON(pud_young(pud_mkold(pud_mkyoung(pud))));
+
+	if (mm_pmd_folded(mm))
+		return;
+
+	/*
+	 * A huge page does not point to next level page table
+	 * entry. Hence this must qualify as pud_bad().
+	 */
+	WARN_ON(!pud_bad(pud_mkhuge(pud)));
+}
+#else
+static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) { }
+#endif
+#else
+static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot) { }
+static void __init pud_basic_tests(unsigned long pfn, pgprot_t prot) { }
+#endif
+
+static void __init p4d_basic_tests(unsigned long pfn, pgprot_t prot)
+{
+	p4d_t p4d;
+
+	memset(&p4d, RANDOM_NZVALUE, sizeof(p4d_t));
+	WARN_ON(!p4d_same(p4d, p4d));
+}
+
+static void __init pgd_basic_tests(unsigned long pfn, pgprot_t prot)
+{
+	pgd_t pgd;
+
+	memset(&pgd, RANDOM_NZVALUE, sizeof(pgd_t));
+	WARN_ON(!pgd_same(pgd, pgd));
+}
+
+#ifndef __PAGETABLE_PUD_FOLDED
+static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp)
+{
+	pud_t pud = READ_ONCE(*pudp);
+
+	if (mm_pmd_folded(mm))
+		return;
+
+	pud = __pud(pud_val(pud) | RANDOM_ORVALUE);
+	WRITE_ONCE(*pudp, pud);
+	pud_clear(pudp);
+	pud = READ_ONCE(*pudp);
+	WARN_ON(!pud_none(pud));
+}
+
+static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
+				      pmd_t *pmdp)
+{
+	pud_t pud;
+
+	if (mm_pmd_folded(mm))
+		return;
+	/*
+	 * This entry points to next level page table page.
+	 * Hence this must not qualify as pud_bad().
+	 */
+	pmd_clear(pmdp);
+	pud_clear(pudp);
+	pud_populate(mm, pudp, pmdp);
+	pud = READ_ONCE(*pudp);
+	WARN_ON(pud_bad(pud));
+}
+#else
+static void __init pud_clear_tests(struct mm_struct *mm, pud_t *pudp) { }
+static void __init pud_populate_tests(struct mm_struct *mm, pud_t *pudp,
+				      pmd_t *pmdp)
+{
+}
+#endif
+
+#ifndef __PAGETABLE_P4D_FOLDED
+static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp)
+{
+	p4d_t p4d = READ_ONCE(*p4dp);
+
+	if (mm_pud_folded(mm))
+		return;
+
+	p4d = __p4d(p4d_val(p4d) | RANDOM_ORVALUE);
+	WRITE_ONCE(*p4dp, p4d);
+	p4d_clear(p4dp);
+	p4d = READ_ONCE(*p4dp);
+	WARN_ON(!p4d_none(p4d));
+}
+
+static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
+				      pud_t *pudp)
+{
+	p4d_t p4d;
+
+	if (mm_pud_folded(mm))
+		return;
+
+	/*
+	 * This entry points to next level page table page.
+	 * Hence this must not qualify as p4d_bad().
+	 */
+	pud_clear(pudp);
+	p4d_clear(p4dp);
+	p4d_populate(mm, p4dp, pudp);
+	p4d = READ_ONCE(*p4dp);
+	WARN_ON(p4d_bad(p4d));
+}
+
+static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp)
+{
+	pgd_t pgd = READ_ONCE(*pgdp);
+
+	if (mm_p4d_folded(mm))
+		return;
+
+	pgd = __pgd(pgd_val(pgd) | RANDOM_ORVALUE);
+	WRITE_ONCE(*pgdp, pgd);
+	pgd_clear(pgdp);
+	pgd = READ_ONCE(*pgdp);
+	WARN_ON(!pgd_none(pgd));
+}
+
+static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
+				      p4d_t *p4dp)
+{
+	pgd_t pgd;
+
+	if (mm_p4d_folded(mm))
+		return;
+
+	/*
+	 * This entry points to next level page table page.
+	 * Hence this must not qualify as pgd_bad().
+	 */
+	p4d_clear(p4dp);
+	pgd_clear(pgdp);
+	pgd_populate(mm, pgdp, p4dp);
+	pgd = READ_ONCE(*pgdp);
+	WARN_ON(pgd_bad(pgd));
+}
+#else
+static void __init p4d_clear_tests(struct mm_struct *mm, p4d_t *p4dp) { }
+static void __init pgd_clear_tests(struct mm_struct *mm, pgd_t *pgdp) { }
+static void __init p4d_populate_tests(struct mm_struct *mm, p4d_t *p4dp,
+				      pud_t *pudp)
+{
+}
+static void __init pgd_populate_tests(struct mm_struct *mm, pgd_t *pgdp,
+				      p4d_t *p4dp)
+{
+}
+#endif
+
+static void __init pte_clear_tests(struct mm_struct *mm, pte_t *ptep)
+{
+	pte_t pte = READ_ONCE(*ptep);
+
+	pte = __pte(pte_val(pte) | RANDOM_ORVALUE);
+	WRITE_ONCE(*ptep, pte);
+	pte_clear(mm, 0, ptep);
+	pte = READ_ONCE(*ptep);
+	WARN_ON(!pte_none(pte));
+}
+
+static void __init pmd_clear_tests(struct mm_struct *mm, pmd_t *pmdp)
+{
+	pmd_t pmd = READ_ONCE(*pmdp);
+
+	pmd = __pmd(pmd_val(pmd) | RANDOM_ORVALUE);
+	WRITE_ONCE(*pmdp, pmd);
+	pmd_clear(pmdp);
+	pmd = READ_ONCE(*pmdp);
+	WARN_ON(!pmd_none(pmd));
+}
+
+static void __init pmd_populate_tests(struct mm_struct *mm, pmd_t *pmdp,
+				      pgtable_t pgtable)
+{
+	pmd_t pmd;
+
+	/*
+	 * This entry points to next level page table page.
+	 * Hence this must not qualify as pmd_bad().
+	 */
+	pmd_clear(pmdp);
+	pmd_populate(mm, pmdp, pgtable);
+	pmd = READ_ONCE(*pmdp);
+	WARN_ON(pmd_bad(pmd));
+}
+
+static unsigned long __init get_random_vaddr(void)
+{
+	unsigned long random_vaddr, random_pages, total_user_pages;
+
+	total_user_pages = (TASK_SIZE - FIRST_USER_ADDRESS) / PAGE_SIZE;
+
+	random_pages = get_random_long() % total_user_pages;
+	random_vaddr = FIRST_USER_ADDRESS + random_pages * PAGE_SIZE;
+
+	return random_vaddr;
+}
+
+void __init debug_vm_pgtable(void)
+{
+	struct mm_struct *mm;
+	pgd_t *pgdp;
+	p4d_t *p4dp, *saved_p4dp;
+	pud_t *pudp, *saved_pudp;
+	pmd_t *pmdp, *saved_pmdp, pmd;
+	pte_t *ptep;
+	pgtable_t saved_ptep;
+	pgprot_t prot;
+	phys_addr_t paddr;
+	unsigned long vaddr, pte_aligned, pmd_aligned;
+	unsigned long pud_aligned, p4d_aligned, pgd_aligned;
+
+	pr_info("Validating architecture page table helpers\n");
+	prot = vm_get_page_prot(VMFLAGS);
+	vaddr = get_random_vaddr();
+	mm = mm_alloc();
+	if (!mm) {
+		pr_err("mm_struct allocation failed\n");
+		return;
+	}
+
+	/*
+	 * PFN for mapping at PTE level is determined from a standard kernel
+	 * text symbol. But pfns for higher page table levels are derived by
+	 * masking lower bits of this real pfn. These derived pfns might not
+	 * exist on the platform but that does not really matter as pfn_pxx()
+	 * helpers will still create appropriate entries for the test. This
+	 * helps avoid large memory block allocations to be used for mapping
+	 * at higher page table levels.
+	 */
+	paddr = __pa(&start_kernel);
+
+	pte_aligned = (paddr & PAGE_MASK) >> PAGE_SHIFT;
+	pmd_aligned = (paddr & PMD_MASK) >> PAGE_SHIFT;
+	pud_aligned = (paddr & PUD_MASK) >> PAGE_SHIFT;
+	p4d_aligned = (paddr & P4D_MASK) >> PAGE_SHIFT;
+	pgd_aligned = (paddr & PGDIR_MASK) >> PAGE_SHIFT;
+	WARN_ON(!pfn_valid(pte_aligned));
+
+	pgdp = pgd_offset(mm, vaddr);
+	p4dp = p4d_alloc(mm, pgdp, vaddr);
+	pudp = pud_alloc(mm, p4dp, vaddr);
+	pmdp = pmd_alloc(mm, pudp, vaddr);
+	ptep = pte_alloc_map(mm, pmdp, vaddr);
+
+	/*
+	 * Save all the page table page addresses as the page table
+	 * entries will be used for testing with random or garbage
+	 * values. These saved addresses will be used for freeing
+	 * page table pages.
+	 */
+	pmd = READ_ONCE(*pmdp);
+	saved_p4dp = p4d_offset(pgdp, 0UL);
+	saved_pudp = pud_offset(p4dp, 0UL);
+	saved_pmdp = pmd_offset(pudp, 0UL);
+	saved_ptep = pmd_pgtable(pmd);
+
+	pte_basic_tests(pte_aligned, prot);
+	pmd_basic_tests(pmd_aligned, prot);
+	pud_basic_tests(pud_aligned, prot);
+	p4d_basic_tests(p4d_aligned, prot);
+	pgd_basic_tests(pgd_aligned, prot);
+
+	pte_clear_tests(mm, ptep);
+	pmd_clear_tests(mm, pmdp);
+	pud_clear_tests(mm, pudp);
+	p4d_clear_tests(mm, p4dp);
+	pgd_clear_tests(mm, pgdp);
+
+	pte_unmap(ptep);
+
+	pmd_populate_tests(mm, pmdp, saved_ptep);
+	pud_populate_tests(mm, pudp, saved_pmdp);
+	p4d_populate_tests(mm, p4dp, saved_pudp);
+	pgd_populate_tests(mm, pgdp, saved_p4dp);
+
+	p4d_free(mm, saved_p4dp);
+	pud_free(mm, saved_pudp);
+	pmd_free(mm, saved_pmdp);
+	pte_free(mm, saved_ptep);
+
+	mm_dec_nr_puds(mm);
+	mm_dec_nr_pmds(mm);
+	mm_dec_nr_ptes(mm);
+	mmdrop(mm);
+}