@@ -17,3 +17,4 @@ Linux x86 Support
zero-page
tlb
mtrr
+ pat
new file mode 100644
@@ -0,0 +1,235 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==========================
+PAT (Page Attribute Table)
+==========================
+
+x86 Page Attribute Table (PAT) allows for setting the memory attribute at the
+page level granularity. PAT is complementary to the MTRR settings which allows
+for setting of memory types over physical address ranges. However, PAT is
+more flexible than MTRR due to its capability to set attributes at page level
+and also due to the fact that there are no hardware limitations on number of
+such attribute settings allowed. Added flexibility comes with guidelines for
+not having memory type aliasing for the same physical memory with multiple
+virtual addresses.
+
+PAT allows for different types of memory attributes. The most commonly used
+ones that will be supported at this time are Write-back, Uncached,
+Write-combined, Write-through and Uncached Minus.
+
+
+PAT APIs
+========
+
+There are many different APIs in the kernel that allows setting of memory
+attributes at the page level. In order to avoid aliasing, these interfaces
+should be used thoughtfully. Below is a table of interfaces available,
+their intended usage and their memory attribute relationships. Internally,
+these APIs use a reserve_memtype()/free_memtype() interface on the physical
+address range to avoid any aliasing.
+::
+
+ -------------------------------------------------------------------
+ API | RAM | ACPI,... | Reserved/Holes |
+ -----------------------|----------|------------|------------------|
+ | | | |
+ ioremap | -- | UC- | UC- |
+ | | | |
+ ioremap_cache | -- | WB | WB |
+ | | | |
+ ioremap_uc | -- | UC | UC |
+ | | | |
+ ioremap_nocache | -- | UC- | UC- |
+ | | | |
+ ioremap_wc | -- | -- | WC |
+ | | | |
+ ioremap_wt | -- | -- | WT |
+ | | | |
+ set_memory_uc | UC- | -- | -- |
+ set_memory_wb | | | |
+ | | | |
+ set_memory_wc | WC | -- | -- |
+ set_memory_wb | | | |
+ | | | |
+ set_memory_wt | WT | -- | -- |
+ set_memory_wb | | | |
+ | | | |
+ pci sysfs resource | -- | -- | UC- |
+ | | | |
+ pci sysfs resource_wc | -- | -- | WC |
+ is IORESOURCE_PREFETCH | | | |
+ | | | |
+ pci proc | -- | -- | UC- |
+ !PCIIOC_WRITE_COMBINE | | | |
+ | | | |
+ pci proc | -- | -- | WC |
+ PCIIOC_WRITE_COMBINE | | | |
+ | | | |
+ /dev/mem | -- | WB/WC/UC- | WB/WC/UC- |
+ read-write | | | |
+ | | | |
+ /dev/mem | -- | UC- | UC- |
+ mmap SYNC flag | | | |
+ | | | |
+ /dev/mem | -- | WB/WC/UC- | WB/WC/UC- |
+ mmap !SYNC flag | |(from exist-| (from exist- |
+ and | | ing alias)| ing alias) |
+ any alias to this area | | | |
+ | | | |
+ /dev/mem | -- | WB | WB |
+ mmap !SYNC flag | | | |
+ no alias to this area | | | |
+ and | | | |
+ MTRR says WB | | | |
+ | | | |
+ /dev/mem | -- | -- | UC- |
+ mmap !SYNC flag | | | |
+ no alias to this area | | | |
+ and | | | |
+ MTRR says !WB | | | |
+ | | | |
+ -------------------------------------------------------------------
+
+Advanced APIs for drivers
+=========================
+
+A. Exporting pages to users with remap_pfn_range, io_remap_pfn_range,
+vmf_insert_pfn.
+
+Drivers wanting to export some pages to userspace do it by using mmap
+interface and a combination of:
+
+ 1) pgprot_noncached()
+ 2) io_remap_pfn_range() or remap_pfn_range() or vmf_insert_pfn()
+
+With PAT support, a new API pgprot_writecombine is being added. So, drivers can
+continue to use the above sequence, with either pgprot_noncached() or
+pgprot_writecombine() in step 1, followed by step 2.
+
+In addition, step 2 internally tracks the region as UC or WC in memtype
+list in order to ensure no conflicting mapping.
+
+Note that this set of APIs only works with IO (non RAM) regions. If driver
+wants to export a RAM region, it has to do set_memory_uc() or set_memory_wc()
+as step 0 above and also track the usage of those pages and use set_memory_wb()
+before the page is freed to free pool.
+
+MTRR effects on PAT / non-PAT systems
+=====================================
+
+The following table provides the effects of using write-combining MTRRs when
+using ioremap*() calls on x86 for both non-PAT and PAT systems. Ideally
+mtrr_add() usage will be phased out in favor of arch_phys_wc_add() which will
+be a no-op on PAT enabled systems. The region over which a arch_phys_wc_add()
+is made, should already have been ioremapped with WC attributes or PAT entries,
+this can be done by using ioremap_wc() / set_memory_wc(). Devices which
+combine areas of IO memory desired to remain uncacheable with areas where
+write-combining is desirable should consider use of ioremap_uc() followed by
+set_memory_wc() to white-list effective write-combined areas. Such use is
+nevertheless discouraged as the effective memory type is considered
+implementation defined, yet this strategy can be used as last resort on devices
+with size-constrained regions where otherwise MTRR write-combining would
+otherwise not be effective.
+::
+
+ ----------------------------------------------------------------------
+ MTRR Non-PAT PAT Linux ioremap value Effective memory type
+ ----------------------------------------------------------------------
+ Non-PAT | PAT
+ PAT
+ |PCD
+ ||PWT
+ |||
+ WC 000 WB _PAGE_CACHE_MODE_WB WC | WC
+ WC 001 WC _PAGE_CACHE_MODE_WC WC* | WC
+ WC 010 UC- _PAGE_CACHE_MODE_UC_MINUS WC* | UC
+ WC 011 UC _PAGE_CACHE_MODE_UC UC | UC
+ ----------------------------------------------------------------------
+
+(*) denotes implementation defined and is discouraged
+
+.. note:: -- in the above table mean "Not suggested usage for the API". Some
+ of the --'s are strictly enforced by the kernel. Some others are not really
+ enforced today, but may be enforced in future.
+
+For ioremap and pci access through /sys or /proc - The actual type returned
+can be more restrictive, in case of any existing aliasing for that address.
+For example: If there is an existing uncached mapping, a new ioremap_wc can
+return uncached mapping in place of write-combine requested.
+
+set_memory_[uc|wc|wt] and set_memory_wb should be used in pairs, where driver
+will first make a region uc, wc or wt and switch it back to wb after use.
+
+Over time writes to /proc/mtrr will be deprecated in favor of using PAT based
+interfaces. Users writing to /proc/mtrr are suggested to use above interfaces.
+
+Drivers should use ioremap_[uc|wc] to access PCI BARs with [uc|wc] access
+types.
+
+Drivers should use set_memory_[uc|wc|wt] to set access type for RAM ranges.
+
+
+PAT debugging
+=============
+
+With CONFIG_DEBUG_FS enabled, PAT memtype list can be examined by::
+
+ # mount -t debugfs debugfs /sys/kernel/debug
+ # cat /sys/kernel/debug/x86/pat_memtype_list
+ PAT memtype list:
+ uncached-minus @ 0x7fadf000-0x7fae0000
+ uncached-minus @ 0x7fb19000-0x7fb1a000
+ uncached-minus @ 0x7fb1a000-0x7fb1b000
+ uncached-minus @ 0x7fb1b000-0x7fb1c000
+ uncached-minus @ 0x7fb1c000-0x7fb1d000
+ uncached-minus @ 0x7fb1d000-0x7fb1e000
+ uncached-minus @ 0x7fb1e000-0x7fb25000
+ uncached-minus @ 0x7fb25000-0x7fb26000
+ uncached-minus @ 0x7fb26000-0x7fb27000
+ uncached-minus @ 0x7fb27000-0x7fb28000
+ uncached-minus @ 0x7fb28000-0x7fb2e000
+ uncached-minus @ 0x7fb2e000-0x7fb2f000
+ uncached-minus @ 0x7fb2f000-0x7fb30000
+ uncached-minus @ 0x7fb31000-0x7fb32000
+ uncached-minus @ 0x80000000-0x90000000
+
+This list shows physical address ranges and various PAT settings used to
+access those physical address ranges.
+
+Another, more verbose way of getting PAT related debug messages is with
+"debugpat" boot parameter. With this parameter, various debug messages are
+printed to dmesg log.
+
+PAT Initialization
+==================
+
+The following table describes how PAT is initialized under various
+configurations. The PAT MSR must be updated by Linux in order to support WC
+and WT attributes. Otherwise, the PAT MSR has the value programmed in it
+by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests.
+::
+
+ MTRR PAT Call Sequence PAT State PAT MSR
+ =========================================================
+ E E MTRR -> PAT init Enabled OS
+ E D MTRR -> PAT init Disabled -
+ D E MTRR -> PAT disable Disabled BIOS
+ D D MTRR -> PAT disable Disabled -
+ - np/E PAT -> PAT disable Disabled BIOS
+ - np/D PAT -> PAT disable Disabled -
+ E !P/E MTRR -> PAT init Disabled BIOS
+ D !P/E MTRR -> PAT disable Disabled BIOS
+ !M !P/E MTRR stub -> PAT disable Disabled BIOS
+
+ Legend
+ ------------------------------------------------
+ E Feature enabled in CPU
+ D Feature disabled/unsupported in CPU
+ np "nopat" boot option specified
+ !P CONFIG_X86_PAT option unset
+ !M CONFIG_MTRR option unset
+ Enabled PAT state set to enabled
+ Disabled PAT state set to disabled
+ OS PAT initializes PAT MSR with OS setting
+ BIOS PAT keeps PAT MSR with BIOS setting
+
deleted file mode 100644
@@ -1,230 +0,0 @@
-
-PAT (Page Attribute Table)
-
-x86 Page Attribute Table (PAT) allows for setting the memory attribute at the
-page level granularity. PAT is complementary to the MTRR settings which allows
-for setting of memory types over physical address ranges. However, PAT is
-more flexible than MTRR due to its capability to set attributes at page level
-and also due to the fact that there are no hardware limitations on number of
-such attribute settings allowed. Added flexibility comes with guidelines for
-not having memory type aliasing for the same physical memory with multiple
-virtual addresses.
-
-PAT allows for different types of memory attributes. The most commonly used
-ones that will be supported at this time are Write-back, Uncached,
-Write-combined, Write-through and Uncached Minus.
-
-
-PAT APIs
---------
-
-There are many different APIs in the kernel that allows setting of memory
-attributes at the page level. In order to avoid aliasing, these interfaces
-should be used thoughtfully. Below is a table of interfaces available,
-their intended usage and their memory attribute relationships. Internally,
-these APIs use a reserve_memtype()/free_memtype() interface on the physical
-address range to avoid any aliasing.
-
-
--------------------------------------------------------------------
-API | RAM | ACPI,... | Reserved/Holes |
------------------------|----------|------------|------------------|
- | | | |
-ioremap | -- | UC- | UC- |
- | | | |
-ioremap_cache | -- | WB | WB |
- | | | |
-ioremap_uc | -- | UC | UC |
- | | | |
-ioremap_nocache | -- | UC- | UC- |
- | | | |
-ioremap_wc | -- | -- | WC |
- | | | |
-ioremap_wt | -- | -- | WT |
- | | | |
-set_memory_uc | UC- | -- | -- |
- set_memory_wb | | | |
- | | | |
-set_memory_wc | WC | -- | -- |
- set_memory_wb | | | |
- | | | |
-set_memory_wt | WT | -- | -- |
- set_memory_wb | | | |
- | | | |
-pci sysfs resource | -- | -- | UC- |
- | | | |
-pci sysfs resource_wc | -- | -- | WC |
- is IORESOURCE_PREFETCH| | | |
- | | | |
-pci proc | -- | -- | UC- |
- !PCIIOC_WRITE_COMBINE | | | |
- | | | |
-pci proc | -- | -- | WC |
- PCIIOC_WRITE_COMBINE | | | |
- | | | |
-/dev/mem | -- | WB/WC/UC- | WB/WC/UC- |
- read-write | | | |
- | | | |
-/dev/mem | -- | UC- | UC- |
- mmap SYNC flag | | | |
- | | | |
-/dev/mem | -- | WB/WC/UC- | WB/WC/UC- |
- mmap !SYNC flag | |(from exist-| (from exist- |
- and | | ing alias)| ing alias) |
- any alias to this area| | | |
- | | | |
-/dev/mem | -- | WB | WB |
- mmap !SYNC flag | | | |
- no alias to this area | | | |
- and | | | |
- MTRR says WB | | | |
- | | | |
-/dev/mem | -- | -- | UC- |
- mmap !SYNC flag | | | |
- no alias to this area | | | |
- and | | | |
- MTRR says !WB | | | |
- | | | |
--------------------------------------------------------------------
-
-Advanced APIs for drivers
--------------------------
-A. Exporting pages to users with remap_pfn_range, io_remap_pfn_range,
-vmf_insert_pfn
-
-Drivers wanting to export some pages to userspace do it by using mmap
-interface and a combination of
-1) pgprot_noncached()
-2) io_remap_pfn_range() or remap_pfn_range() or vmf_insert_pfn()
-
-With PAT support, a new API pgprot_writecombine is being added. So, drivers can
-continue to use the above sequence, with either pgprot_noncached() or
-pgprot_writecombine() in step 1, followed by step 2.
-
-In addition, step 2 internally tracks the region as UC or WC in memtype
-list in order to ensure no conflicting mapping.
-
-Note that this set of APIs only works with IO (non RAM) regions. If driver
-wants to export a RAM region, it has to do set_memory_uc() or set_memory_wc()
-as step 0 above and also track the usage of those pages and use set_memory_wb()
-before the page is freed to free pool.
-
-MTRR effects on PAT / non-PAT systems
--------------------------------------
-
-The following table provides the effects of using write-combining MTRRs when
-using ioremap*() calls on x86 for both non-PAT and PAT systems. Ideally
-mtrr_add() usage will be phased out in favor of arch_phys_wc_add() which will
-be a no-op on PAT enabled systems. The region over which a arch_phys_wc_add()
-is made, should already have been ioremapped with WC attributes or PAT entries,
-this can be done by using ioremap_wc() / set_memory_wc(). Devices which
-combine areas of IO memory desired to remain uncacheable with areas where
-write-combining is desirable should consider use of ioremap_uc() followed by
-set_memory_wc() to white-list effective write-combined areas. Such use is
-nevertheless discouraged as the effective memory type is considered
-implementation defined, yet this strategy can be used as last resort on devices
-with size-constrained regions where otherwise MTRR write-combining would
-otherwise not be effective.
-
-----------------------------------------------------------------------
-MTRR Non-PAT PAT Linux ioremap value Effective memory type
-----------------------------------------------------------------------
- Non-PAT | PAT
- PAT
- |PCD
- ||PWT
- |||
-WC 000 WB _PAGE_CACHE_MODE_WB WC | WC
-WC 001 WC _PAGE_CACHE_MODE_WC WC* | WC
-WC 010 UC- _PAGE_CACHE_MODE_UC_MINUS WC* | UC
-WC 011 UC _PAGE_CACHE_MODE_UC UC | UC
-----------------------------------------------------------------------
-
-(*) denotes implementation defined and is discouraged
-
-Notes:
-
-are strictly enforced by the kernel. Some others are not really enforced
-today, but may be enforced in future.
-
-For ioremap and pci access through /sys or /proc - The actual type returned
-can be more restrictive, in case of any existing aliasing for that address.
-For example: If there is an existing uncached mapping, a new ioremap_wc can
-return uncached mapping in place of write-combine requested.
-
-set_memory_[uc|wc|wt] and set_memory_wb should be used in pairs, where driver
-will first make a region uc, wc or wt and switch it back to wb after use.
-
-Over time writes to /proc/mtrr will be deprecated in favor of using PAT based
-interfaces. Users writing to /proc/mtrr are suggested to use above interfaces.
-
-Drivers should use ioremap_[uc|wc] to access PCI BARs with [uc|wc] access
-types.
-
-Drivers should use set_memory_[uc|wc|wt] to set access type for RAM ranges.
-
-
-PAT debugging
--------------
-
-With CONFIG_DEBUG_FS enabled, PAT memtype list can be examined by
-
-# mount -t debugfs debugfs /sys/kernel/debug
-# cat /sys/kernel/debug/x86/pat_memtype_list
-PAT memtype list:
-uncached-minus @ 0x7fadf000-0x7fae0000
-uncached-minus @ 0x7fb19000-0x7fb1a000
-uncached-minus @ 0x7fb1a000-0x7fb1b000
-uncached-minus @ 0x7fb1b000-0x7fb1c000
-uncached-minus @ 0x7fb1c000-0x7fb1d000
-uncached-minus @ 0x7fb1d000-0x7fb1e000
-uncached-minus @ 0x7fb1e000-0x7fb25000
-uncached-minus @ 0x7fb25000-0x7fb26000
-uncached-minus @ 0x7fb26000-0x7fb27000
-uncached-minus @ 0x7fb27000-0x7fb28000
-uncached-minus @ 0x7fb28000-0x7fb2e000
-uncached-minus @ 0x7fb2e000-0x7fb2f000
-uncached-minus @ 0x7fb2f000-0x7fb30000
-uncached-minus @ 0x7fb31000-0x7fb32000
-uncached-minus @ 0x80000000-0x90000000
-
-This list shows physical address ranges and various PAT settings used to
-access those physical address ranges.
-
-Another, more verbose way of getting PAT related debug messages is with
-"debugpat" boot parameter. With this parameter, various debug messages are
-printed to dmesg log.
-
-PAT Initialization
-------------------
-
-The following table describes how PAT is initialized under various
-configurations. The PAT MSR must be updated by Linux in order to support WC
-and WT attributes. Otherwise, the PAT MSR has the value programmed in it
-by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests.
-
- MTRR PAT Call Sequence PAT State PAT MSR
- =========================================================
- E E MTRR -> PAT init Enabled OS
- E D MTRR -> PAT init Disabled -
- D E MTRR -> PAT disable Disabled BIOS
- D D MTRR -> PAT disable Disabled -
- - np/E PAT -> PAT disable Disabled BIOS
- - np/D PAT -> PAT disable Disabled -
- E !P/E MTRR -> PAT init Disabled BIOS
- D !P/E MTRR -> PAT disable Disabled BIOS
- !M !P/E MTRR stub -> PAT disable Disabled BIOS
-
- Legend
- ------------------------------------------------
- E Feature enabled in CPU
- D Feature disabled/unsupported in CPU
- np "nopat" boot option specified
- !P CONFIG_X86_PAT option unset
- !M CONFIG_MTRR option unset
- Enabled PAT state set to enabled
- Disabled PAT state set to disabled
- OS PAT initializes PAT MSR with OS setting
- BIOS PAT keeps PAT MSR with BIOS setting
-
This converts the plain text documentation to reStructuredText format and add it to Sphinx TOC tree. No essential content change. Signed-off-by: Changbin Du <changbin.du@gmail.com> --- Documentation/x86/index.rst | 1 + Documentation/x86/pat.rst | 235 ++++++++++++++++++++++++++++++++++++ Documentation/x86/pat.txt | 230 ----------------------------------- 3 files changed, 236 insertions(+), 230 deletions(-) create mode 100644 Documentation/x86/pat.rst delete mode 100644 Documentation/x86/pat.txt