Re: [PATCH v10 09/12] powerpc: mm: Add common pud_pfn stub for all platforms
From: Christophe Leroy <hidden>
Date: 2024-03-13 11:08:13
Also in:
linux-arm-kernel, linux-mm, linux-riscv
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.
quoted hunk ↗ jump to hunk
Signed-off-by: Rohan McLure <redacted> --- 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 */