[PATCH v8 0/3] fix double page fault on arm64

[Jia He <justin.he@arm.com>]

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
v8: change cow_user_page's return type (Matthew)
v7: s/pte_spinlock/pte_offset_map_lock (Kirill)
v6: fix error case of returning with spinlock taken (Catalin)
    move kmap_atomic to avoid handling kunmap_atomic
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 (Kirill A. Shutemov)
    add arch_faults_on_old_pte (Matthew, Catalin)
v2: remove FAULT_FLAG_WRITE when setting pte access flag (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 | 10 +++++
 arch/arm64/include/asm/pgtable.h    | 12 ++++++
 mm/memory.c                         | 67 ++++++++++++++++++++++++++---
 3 files changed, 83 insertions(+), 6 deletions(-)

-- 
2.17.1