From 6af31226d0394691f5562eca0134262bb935fa9c Mon Sep 17 00:00:00 2001 From: Jia He Date: Fri, 11 Oct 2019 22:09:37 +0800 Subject: [PATCH] arm64: mm: implement arch_faults_on_old_pte() on arm64 On arm64 without hardware Access Flag, copying from user will fail because the pte is old and cannot be marked young. So we always end up with zeroed page after fork() + CoW for pfn mappings. We don't always have a hardware-managed Access Flag on arm64. Hence implement arch_faults_on_old_pte on arm64 to indicate that it might cause page fault when accessing old pte. Signed-off-by: Jia He Reviewed-by: Catalin Marinas Signed-off-by: Catalin Marinas --- arch/arm64/include/asm/pgtable.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h index 7576df0..e96fb82 100644 --- a/arch/arm64/include/asm/pgtable.h +++ b/arch/arm64/include/asm/pgtable.h @@ -885,6 +885,20 @@ static inline void update_mmu_cache(struct vm_area_struct *vma, #define phys_to_ttbr(addr) (addr) #endif +/* + * On arm64 without hardware Access Flag, copying from user will fail because + * the pte is old and cannot be marked young. So we always end up with zeroed + * page after fork() + CoW for pfn mappings. We don't always have a + * hardware-managed access flag on arm64. + */ +static inline bool arch_faults_on_old_pte(void) +{ + WARN_ON(preemptible()); + + return !cpu_has_hw_af(); +} +#define arch_faults_on_old_pte arch_faults_on_old_pte + #endif /* !__ASSEMBLY__ */ #endif /* __ASM_PGTABLE_H */ -- 2.7.4