[v3,0/2] fix double page fault on arm64

Message

Jia He Sept. 13, 2019, 4:32 p.m. UTC

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
v3: add vmf->ptl lock/unlock (by Kirill A. Shutemov)
    add arch_faults_on_old_pte (Matthew, Catalins)
v2: remove FAULT_FLAG_WRITE when setting pte access flag (by Catalin)
Jia He (2):
  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/pgtable.h | 11 +++++++++++
 mm/memory.c                      | 29 ++++++++++++++++++++++++-----
 2 files changed, 35 insertions(+), 5 deletions(-)