| Message ID | 20240313042118.230397-10-rmclure@linux.ibm.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Support page table check PowerPC | expand |
Le 13/03/2024 à 05:21, Rohan McLure a écrit : > Prior to this commit, pud_pfn was implemented with BUILD_BUG as the inline > function for 64-bit Book3S systems but is never included, as its > invocations in generic code are guarded by calls to pud_devmap which return > zero on such systems. A future patch will provide support for page table > checks, the generic code for which depends on a pud_pfn stub being > implemented, even while the patch will not interact with puds directly. > > Remove the 64-bit Book3S stub and define pud_pfn to warn on all > platforms. pud_pfn may be defined properly on a per-platform basis > should it grow real usages in future. Can you please re-explain why that's needed ? I remember we discussed it already in the past, but I checked again today and can't see the need: In mm/page_table_check.c, the call to pud_pfn() is gated by a call to pud_user_accessible_page(pud). If I look into arm64 version of pud_user_accessible_page(), it depends on pud_leaf(). When pud_leaf() is constant 0, pud_user_accessible_page() is always false and the call to pud_pfn() should be folded away. > > Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> > --- > arch/powerpc/include/asm/pgtable.h | 14 ++++++++++++++ > 1 file changed, 14 insertions(+) > > diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h > index 0c0ffbe7a3b5..13f661831333 100644 > --- a/arch/powerpc/include/asm/pgtable.h > +++ b/arch/powerpc/include/asm/pgtable.h > @@ -213,6 +213,20 @@ static inline bool arch_supports_memmap_on_memory(unsigned long vmemmap_size) > > #endif /* CONFIG_PPC64 */ > > +/* > + * Currently only consumed by page_table_check_pud_{set,clear}. Since clears > + * and sets to page table entries at any level are done through > + * page_table_check_pte_{set,clear}, provide stub implementation. > + */ > +#ifndef pud_pfn > +#define pud_pfn pud_pfn > +static inline int pud_pfn(pud_t pud) > +{ > + WARN_ONCE(1, "pud: platform does not use pud entries directly"); > + return 0; > +} > +#endif > + > #endif /* __ASSEMBLY__ */ > > #endif /* _ASM_POWERPC_PGTABLE_H */
On Wed, 2024-03-13 at 11:08 +0000, Christophe Leroy wrote: > > > Le 13/03/2024 à 05:21, Rohan McLure a écrit : > > Prior to this commit, pud_pfn was implemented with BUILD_BUG as the > > inline > > function for 64-bit Book3S systems but is never included, as its > > invocations in generic code are guarded by calls to pud_devmap > > which return > > zero on such systems. A future patch will provide support for page > > table > > checks, the generic code for which depends on a pud_pfn stub being > > implemented, even while the patch will not interact with puds > > directly. > > > > Remove the 64-bit Book3S stub and define pud_pfn to warn on all > > platforms. pud_pfn may be defined properly on a per-platform basis > > should it grow real usages in future. Apologies, I don't actually remove the 64-bit, Book3S stub, as it currently correctly reflects how transparent hugepages should work. Also the stub that was previously implemented for all platforms has been removed in commit 27af67f35631 ("powerpc/book3s64/mm: enable transparent pud hugepage"). > > Can you please re-explain why that's needed ? I remember we discussed > it > already in the past, but I checked again today and can't see the > need: > > In mm/page_table_check.c, the call to pud_pfn() is gated by a call to > pud_user_accessible_page(pud). If I look into arm64 version of > pud_user_accessible_page(), it depends on pud_leaf(). When pud_leaf() > is > constant 0, pud_user_accessible_page() is always false and the call > to > pud_pfn() should be folded away. As it will be folded away on non 64-bit Book3S platforms, I could even replace the WARN_ONCE with a BUILD_BUG for your stated reason. The __page_table_check_pud_set() function will still be included in the build and references this routine so a fallback stub is still necessary. > > > > > Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> > > --- > > arch/powerpc/include/asm/pgtable.h | 14 ++++++++++++++ > > 1 file changed, 14 insertions(+) > > > > diff --git a/arch/powerpc/include/asm/pgtable.h > > b/arch/powerpc/include/asm/pgtable.h > > index 0c0ffbe7a3b5..13f661831333 100644 > > --- a/arch/powerpc/include/asm/pgtable.h > > +++ b/arch/powerpc/include/asm/pgtable.h > > @@ -213,6 +213,20 @@ static inline bool > > arch_supports_memmap_on_memory(unsigned long vmemmap_size) > > > > #endif /* CONFIG_PPC64 */ > > > > +/* > > + * Currently only consumed by page_table_check_pud_{set,clear}. > > Since clears > > + * and sets to page table entries at any level are done through > > + * page_table_check_pte_{set,clear}, provide stub implementation. > > + */ > > +#ifndef pud_pfn > > +#define pud_pfn pud_pfn > > +static inline int pud_pfn(pud_t pud) > > +{ > > + WARN_ONCE(1, "pud: platform does not use pud entries > > directly"); > > + return 0; > > +} > > +#endif > > + > > #endif /* __ASSEMBLY__ */ > > > > #endif /* _ASM_POWERPC_PGTABLE_H */
diff --git a/arch/powerpc/include/asm/pgtable.h b/arch/powerpc/include/asm/pgtable.h index 0c0ffbe7a3b5..13f661831333 100644 --- a/arch/powerpc/include/asm/pgtable.h +++ b/arch/powerpc/include/asm/pgtable.h @@ -213,6 +213,20 @@ static inline bool arch_supports_memmap_on_memory(unsigned long vmemmap_size) #endif /* CONFIG_PPC64 */ +/* + * Currently only consumed by page_table_check_pud_{set,clear}. Since clears + * and sets to page table entries at any level are done through + * page_table_check_pte_{set,clear}, provide stub implementation. + */ +#ifndef pud_pfn +#define pud_pfn pud_pfn +static inline int pud_pfn(pud_t pud) +{ + WARN_ONCE(1, "pud: platform does not use pud entries directly"); + return 0; +} +#endif + #endif /* __ASSEMBLY__ */ #endif /* _ASM_POWERPC_PGTABLE_H */
Prior to this commit, pud_pfn was implemented with BUILD_BUG as the inline function for 64-bit Book3S systems but is never included, as its invocations in generic code are guarded by calls to pud_devmap which return zero on such systems. A future patch will provide support for page table checks, the generic code for which depends on a pud_pfn stub being implemented, even while the patch will not interact with puds directly. Remove the 64-bit Book3S stub and define pud_pfn to warn on all platforms. pud_pfn may be defined properly on a per-platform basis should it grow real usages in future. Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> --- arch/powerpc/include/asm/pgtable.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+)