| Message ID | 1489767002.3063.10.camel@linaro.org |
|---|---|
| State | New |
| Headers | show |
On 17 March 2017 at 16:10, Jon Medhurst (Tixy) <tixy@linaro.org> wrote: > On Fri, 2017-03-17 at 11:53 +0000, Russell King - ARM Linux wrote: >> On Thu, Mar 16, 2017 at 01:29:57PM +0000, Jon Medhurst wrote: >> > To cope with the variety in ARM architectures and configurations, the >> > pagetable attributes for kernel memory are generated at runtime to match >> > the system the kernel finds itself on. This calculated value is stored >> > in pgprot_kernel. >> > >> > However, when early fixmap support was added for arm (commit >> > a5f4c561b3b1) the attributes used for mappings were hard coded because >> > pgprot_kernel is not set up early enough. Unfortunately, the values used >> > didn't include the 'shareable' attribute which means that for later >> > non-early fixmap use, when multiple CPUs are running, any cache entries >> > allocated for fixmap memory aren't kept consistent between CPUs. This >> > can result in different CPUs seeing different memory contents. >> >> This also likely causes unpredictable behaviour (aliased attributes). >> >> > This issue was discovered on a dual cluster system by failures with >> > kprobes, which uses fixmap to modify the kernel image if >> > CONFIG_DEBUG_RODATA is enabled. It will also affect kgdb and jump_labels >> > which also make use of the same code to modify the kernel, and any other >> > uses of fixmap after secondary CPUs are brought online. >> > >> > To fix this issue, and to help avoid other potential problems where >> > pagetable attributes are incorrect, we change the fixmap code to use the >> > same generated value in pgprot_kernel that the rest of the kernel uses, >> > and only fall back to a hard coded value if this isn't set - which will >> > be early on in boot before other CPUs are brought online. >> >> I'm not happy with this - if we need to create early fixmaps, then >> we need to know the correct attributes to use, so let's move the >> attribute initialisation earlier. This solution feels too much like >> hacking around the problem. > > I must admit to having similar thoughts and plead guilty to ignoring > them. Not knowing how early fixmaps are being used I let myself think > 'it must have been originally done this way for a reason'. > > It looks to me that build_mem_type_table doesn't have much in the way of > dependencies so can probably be just called earlier. So, is the correct > solution to > > a) call build_mem_type_table from setup_arch before early_fixmap_init > b) move call to build_mem_type_table into early_fixmap_init > c) call build_mem_type_table from early_fixmap_init as well as > paging_init and have a test in build_mem_type_table so it only exectutes > once > d) something else > > a) seems simplest, b) seems wrong, c) seems over the top > > Anyway, below is an alternative to $subject patch that works for my > kprobes test cases. Note, the removal of FIXMAP_PAGE_{NORMAL,RO} means > the generic fixmap code will define these from PAGE_KERNEL{,_RO}. > > Not knowing how early fixmap is used, I hope Stefan and/or Ard have > testcases they could run. > The early UEFI boot code maps firmware tables using early_ioremap(), which is layered on top of early_fixmap(). This code executes after early_ioremap_init(), so moving build_mem_type_table() before that sounds like the obvious fix to me. The other use case is earlycon, which uses early_fixmap() directly, but afaict, the same applies there as well. In terms of code changes, there is a d) option where the call sequence build_mem_type/early_fixmap_init/early_ioremap_init is grouped into a new function in mm/mmu.c, which you can call from setup_arch(). That would be the cleanest approach imo. > I'm also wondering if the existing definition of FIXMAP_PAGE_IO is > correc > t and should not also be based on some platform specific value > calculated > in build_mem_type_table? > > > diff --git a/arch/arm/include/asm/fixmap.h > b/arch/arm/include/asm/fixmap.h > index 5c17d2dec777..30871fb269f0 100644 > --- a/arch/arm/include/asm/fixmap.h > +++ b/arch/arm/include/asm/fixmap.h > @@ -41,9 +41,6 @@ static const enum fixed_addresses > __end_of_fixed_addresses = > > #define FIXMAP_PAGE_COMMON (L_PTE_YOUNG | L_PTE_PRESENT | > L_PTE_XN | L_PTE_DIRTY) > > -#define FIXMAP_PAGE_NORMAL (FIXMAP_PAGE_COMMON | > L_PTE_MT_WRITEBACK) > -#define FIXMAP_PAGE_RO (FIXMAP_PAGE_NORMAL | > L_PTE_RDONLY) > - > /* Used by set_fixmap_(io|nocache), both meant for mapping a device */ > #define FIXMAP_PAGE_IO (FIXMAP_PAGE_COMMON | > L_PTE_MT_DEV_SHARED | L_PTE_SHARED) > #define FIXMAP_PAGE_NOCACHE FIXMAP_PAGE_IO > diff --git a/arch/arm/include/asm/pgtable.h > b/arch/arm/include/asm/pgtable.h > index 1c462381c225..6a98856a8fa9 100644 > --- a/arch/arm/include/asm/pgtable.h > +++ b/arch/arm/include/asm/pgtable.h > @@ -98,6 +98,7 @@ extern pgprot_t pgprot_s2_device; > #define PAGE_READONLY_EXEC _MOD_PROT(pgprot_user, L_PTE_USER | > L_PTE_RDONLY) > #define PAGE_KERNEL _MOD_PROT(pgprot_kernel, L_PTE_XN) > #define PAGE_KERNEL_EXEC pgprot_kernel > +#define PAGE_KERNEL_RO _MOD_PROT(pgprot_kernel, L_PTE_XN > | L_PTE_RDONLY) > #define PAGE_HYP _MOD_PROT(pgprot_kernel, L_PTE_HYP | > L_PTE_XN) > #define PAGE_HYP_EXEC _MOD_PROT(pgprot_kernel, L_PTE_HYP > | L_PTE_RDONLY) > #define PAGE_HYP_RO _MOD_PROT(pgprot_kernel, L_PTE_HYP | > L_PTE_RDONLY | L_PTE_XN) > diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c > index f4e54503afa9..fc4782fa5071 100644 > --- a/arch/arm/kernel/setup.c > +++ b/arch/arm/kernel/setup.c > @@ -79,6 +79,7 @@ __setup("fpe=", fpe_setup); > #endif > > extern void init_default_cache_policy(unsigned long); > +extern void build_mem_type_table(void); > extern void paging_init(const struct machine_desc *desc); > extern void early_paging_init(const struct machine_desc *); > extern void adjust_lowmem_bounds(void); > @@ -1082,6 +1083,8 @@ void __init setup_arch(char **cmdline_p) > strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE); > *cmdline_p = cmd_line; > > + build_mem_type_table(); > + > early_fixmap_init(); > early_ioremap_init(); > > diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c > index 4e016d7f37b3..c8e1de3ceb02 100644 > --- a/arch/arm/mm/mmu.c > +++ b/arch/arm/mm/mmu.c > @@ -425,7 +425,7 @@ void __set_fixmap(enum fixed_addresses idx, > phys_addr_t phys, pgprot_t prot) > /* > * Adjust the PMD section entries according to the CPU in use. > */ > -static void __init build_mem_type_table(void) > +void __init build_mem_type_table(void) > { > struct cachepolicy *cp; > unsigned int cr = get_cr(); > @@ -1616,7 +1616,6 @@ void __init paging_init(const struct machine_desc > *mdesc) > { > void *zero_page; > > - build_mem_type_table(); > prepare_page_table(); > map_lowmem(); > memblock_set_current_limit(arm_lowmem_limit); > -- > 2.11.0 > >
On Fri, 2017-03-17 at 16:18 +0000, Ard Biesheuvel wrote: > On 17 March 2017 at 16:10, Jon Medhurst (Tixy) <tixy@linaro.org> wrote: > > [...] > > It looks to me that build_mem_type_table doesn't have much in the way of > > dependencies so can probably be just called earlier. So, is the correct > > solution to > > > > a) call build_mem_type_table from setup_arch before early_fixmap_init > > b) move call to build_mem_type_table into early_fixmap_init > > c) call build_mem_type_table from early_fixmap_init as well as > > paging_init and have a test in build_mem_type_table so it only exectutes > > once > > d) something else > > > > a) seems simplest, b) seems wrong, c) seems over the top > > > > Anyway, below is an alternative to $subject patch that works for my > > kprobes test cases. Note, the removal of FIXMAP_PAGE_{NORMAL,RO} means > > the generic fixmap code will define these from PAGE_KERNEL{,_RO}. > > > > Not knowing how early fixmap is used, I hope Stefan and/or Ard have > > testcases they could run. > > > > The early UEFI boot code maps firmware tables using early_ioremap(), > which is layered on top of early_fixmap(). This code executes after > early_ioremap_init(), so moving build_mem_type_table() before that > sounds like the obvious fix to me. The other use case is earlycon, > which uses early_fixmap() directly, but afaict, the same applies there > as well. So is that 'code should work, no need to test'? Guess it should be safe to skip if those use cases use FIXMAP_PAGE_NOCACHE and FIXMAP_PAGE_IO and we don't change those defines. > In terms of code changes, there is a d) option where the call sequence > build_mem_type/early_fixmap_init/early_ioremap_init is grouped into a > new function in mm/mmu.c, which you can call from setup_arch(). That > would be the cleanest approach imo. Any suggestion on a name for that function? > > > I'm also wondering if the existing definition of FIXMAP_PAGE_IO is > > correc > > t and should not also be based on some platform specific value > > calculated > > in build_mem_type_table? Answering myself. FIXMAP_PAGE_IO is defined with the same values as mem_types[MT_DEVICE].prot_pte which doesn't get modified at runtime, so should be correct... Unless the device being mapped needs Non-shareable Device memory (MT_DEVICE_NONSHARED) in which case we're onto dodgy ground. I can't see how we can detect that in code or help someone using the API to avoid that. I certainly don't intend trying to redesign the API and implementation of early_ioremap to fix these limitations.
On 20 March 2017 at 19:09, Jon Medhurst (Tixy) <tixy@linaro.org> wrote: > On Fri, 2017-03-17 at 16:18 +0000, Ard Biesheuvel wrote: >> On 17 March 2017 at 16:10, Jon Medhurst (Tixy) <tixy@linaro.org> wrote: >> > > [...] >> > It looks to me that build_mem_type_table doesn't have much in the way of >> > dependencies so can probably be just called earlier. So, is the correct >> > solution to >> > >> > a) call build_mem_type_table from setup_arch before early_fixmap_init >> > b) move call to build_mem_type_table into early_fixmap_init >> > c) call build_mem_type_table from early_fixmap_init as well as >> > paging_init and have a test in build_mem_type_table so it only exectutes >> > once >> > d) something else >> > >> > a) seems simplest, b) seems wrong, c) seems over the top >> > >> > Anyway, below is an alternative to $subject patch that works for my >> > kprobes test cases. Note, the removal of FIXMAP_PAGE_{NORMAL,RO} means >> > the generic fixmap code will define these from PAGE_KERNEL{,_RO}. >> > >> > Not knowing how early fixmap is used, I hope Stefan and/or Ard have >> > testcases they could run. >> > >> >> The early UEFI boot code maps firmware tables using early_ioremap(), >> which is layered on top of early_fixmap(). This code executes after >> early_ioremap_init(), so moving build_mem_type_table() before that >> sounds like the obvious fix to me. The other use case is earlycon, >> which uses early_fixmap() directly, but afaict, the same applies there >> as well. > > So is that 'code should work, no need to test'? Guess it should be safe > to skip if those use cases use FIXMAP_PAGE_NOCACHE and FIXMAP_PAGE_IO > and we don't change those defines. > In fact, the UEFI code uses early_memremap() not early_ioremap(), and it does use the memory defines, not the device ones. So yes, I should test it, but I don't see any reason for huge concern, given that the UEFI code maps and unmaps those tables when we're still running UP >> In terms of code changes, there is a d) option where the call sequence >> build_mem_type/early_fixmap_init/early_ioremap_init is grouped into a >> new function in mm/mmu.c, which you can call from setup_arch(). That >> would be the cleanest approach imo. > > Any suggestion on a name for that function? > early_mm_init? >> >> > I'm also wondering if the existing definition of FIXMAP_PAGE_IO is >> > correc >> > t and should not also be based on some platform specific value >> > calculated >> > in build_mem_type_table? > > Answering myself. FIXMAP_PAGE_IO is defined with the same values as > mem_types[MT_DEVICE].prot_pte which doesn't get modified at runtime, so > should be correct... Unless the device being mapped needs Non-shareable > Device memory (MT_DEVICE_NONSHARED) in which case we're onto dodgy > ground. I can't see how we can detect that in code or help someone using > the API to avoid that. I certainly don't intend trying to redesign the > API and implementation of early_ioremap to fix these limitations. > > -- > Tixy >
diff --git a/arch/arm/include/asm/fixmap.h b/arch/arm/include/asm/fixmap.h index 5c17d2dec777..30871fb269f0 100644 --- a/arch/arm/include/asm/fixmap.h +++ b/arch/arm/include/asm/fixmap.h @@ -41,9 +41,6 @@ static const enum fixed_addresses __end_of_fixed_addresses = #define FIXMAP_PAGE_COMMON (L_PTE_YOUNG | L_PTE_PRESENT | L_PTE_XN | L_PTE_DIRTY) -#define FIXMAP_PAGE_NORMAL (FIXMAP_PAGE_COMMON | L_PTE_MT_WRITEBACK) -#define FIXMAP_PAGE_RO (FIXMAP_PAGE_NORMAL | L_PTE_RDONLY) - /* Used by set_fixmap_(io|nocache), both meant for mapping a device */ #define FIXMAP_PAGE_IO (FIXMAP_PAGE_COMMON | L_PTE_MT_DEV_SHARED | L_PTE_SHARED) #define FIXMAP_PAGE_NOCACHE FIXMAP_PAGE_IO diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h index 1c462381c225..6a98856a8fa9 100644 --- a/arch/arm/include/asm/pgtable.h +++ b/arch/arm/include/asm/pgtable.h @@ -98,6 +98,7 @@ extern pgprot_t pgprot_s2_device; #define PAGE_READONLY_EXEC _MOD_PROT(pgprot_user, L_PTE_USER | L_PTE_RDONLY) #define PAGE_KERNEL _MOD_PROT(pgprot_kernel, L_PTE_XN) #define PAGE_KERNEL_EXEC pgprot_kernel +#define PAGE_KERNEL_RO _MOD_PROT(pgprot_kernel, L_PTE_XN | L_PTE_RDONLY) #define PAGE_HYP _MOD_PROT(pgprot_kernel, L_PTE_HYP | L_PTE_XN) #define PAGE_HYP_EXEC _MOD_PROT(pgprot_kernel, L_PTE_HYP | L_PTE_RDONLY) #define PAGE_HYP_RO _MOD_PROT(pgprot_kernel, L_PTE_HYP | L_PTE_RDONLY | L_PTE_XN) diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c index f4e54503afa9..fc4782fa5071 100644 --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -79,6 +79,7 @@ __setup("fpe=", fpe_setup); #endif extern void init_default_cache_policy(unsigned long); +extern void build_mem_type_table(void); extern void paging_init(const struct machine_desc *desc); extern void early_paging_init(const struct machine_desc *); extern void adjust_lowmem_bounds(void); @@ -1082,6 +1083,8 @@ void __init setup_arch(char **cmdline_p) strlcpy(cmd_line, boot_command_line, COMMAND_LINE_SIZE); *cmdline_p = cmd_line; + build_mem_type_table(); + early_fixmap_init(); early_ioremap_init(); diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c index 4e016d7f37b3..c8e1de3ceb02 100644 --- a/arch/arm/mm/mmu.c +++ b/arch/arm/mm/mmu.c @@ -425,7 +425,7 @@ void __set_fixmap(enum fixed_addresses idx, phys_addr_t phys, pgprot_t prot) /* * Adjust the PMD section entries according to the CPU in use. */ -static void __init build_mem_type_table(void) +void __init build_mem_type_table(void) { struct cachepolicy *cp;