Commit 6af31226 authored Oct 11, 2019 by Jia He Committed by Catalin Marinas Oct 18, 2019

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 <justin.he@arm.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

parent 47d7b15b

arch/arm64/include/asm/pgtable.h

+14 −0

Original line number	Diff line number	Diff line
		@@ -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 */

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