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UPSTREAM: 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.
Moto-CRs-Fixed:(CR)

Link: https://lore.kernel.org/r/20191011140939.6115-3-justin.he@arm.com/
Change-Id: Ica230a882941cb17a1acdd6c6c9f3ec1b3f494b3
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>
(cherry picked from commit 6af31226d0394691f5562eca0134262bb935fa9c)
Bug: 261052246
Signed-off-by: Kalesh Singh <kaleshsingh@google.com>
Reviewed-on: https://gerrit.mot.com/2491777
SME-Granted: SME Approvals Granted
SLTApproved: Slta Waiver
Tested-by: Jira Key
Reviewed-by: Xiangpo Zhao <zhaoxp3@motorola.com>
Submit-Approved: Jira Key
This commit is contained in:
Jia He 2019-10-11 22:09:37 +08:00 • committed by Xiaojun Ji
commit adb8e3c5c0
1 changed files with 14 additions and 0 deletions
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14
arch/arm64/include/asm/pgtable.h
View file

@ -886,6 +886,20 @@ 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 */