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

From: Jia He
Date: Fri Sep 13 2019 - 12:32:54 EST

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."

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(-)