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arm64: mm: implement arch_faults_on_old_pte() on arm64

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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 <justin.he@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
This commit is contained in:
Jia He 2019-10-11 22:09:37 +08:00 committed by Catalin Marinas
parent 47d7b15b88
commit 6af31226d0
1 changed files with 14 additions and 0 deletions
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14
arch/arm64/include/asm/pgtable.h
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@ -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 */