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
