Subject: [PATCH v5 0/3] fix double page fault on arm64

From: Jia He <[email-masked]>
Date: Fri, 20 Sep 2019 00:12:01 +0800

When we tested pmdk unit test vmmalloc_fork TEST1 in arm64 guest, there
will be a double page fault in __copy_from_user_inatomic of cow_user_page.

As told by Catalin: "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."

Changes
v5: handle the case correctly when !pte_same
    fix kbuild test failed
v4: introduce cpu_has_hw_af (Suzuki)
    bail out if !pte_same (Kirill)
v3: add vmf->ptl lock/unlock (by Kirill A. Shutemov)
    add arch_faults_on_old_pte (Matthew, Catalin)
v2: remove FAULT_FLAG_WRITE when setting pte access flag (by Catalin)

Jia He (3):
  arm64: cpufeature: introduce helper cpu_has_hw_af()
  arm64: mm: implement arch_faults_on_old_pte() on arm64
  mm: fix double page fault on arm64 if PTE_AF is cleared

 arch/arm64/include/asm/cpufeature.h |  1 +
 arch/arm64/include/asm/pgtable.h    | 12 ++++++
 arch/arm64/kernel/cpufeature.c      | 10 +++++
 mm/memory.c                         | 59 ++++++++++++++++++++++++++---
 4 files changed, 77 insertions(+), 5 deletions(-)

-- 
2.17.1

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