Re: [PATCH v12 0/4] fix double page fault in cow_user_page for pfn mapping
On Tue, Oct 15, 2019 at 01:18:34AM +0100, Will Deacon wrote: > On Fri, Oct 11, 2019 at 10:09:35PM +0800, Jia He wrote: > > 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 > > v12: > > refine PATCH 01, remove the !! since C languages can convert unsigned > > to bool (Catalin) > > Thanks. I think it's a bit late to take something like this for 5.4 now, > especially as the current behaviour has always been there. Hopefully > somebody can queue it for 5.5 instead. I can queue this through the arm64 tree for 5.5 if I get an ack on the x86 patch (3/4) or I don't hear any complaints. -- Catalin
Re: [PATCH v12 0/4] fix double page fault in cow_user_page for pfn mapping
On Fri, Oct 11, 2019 at 10:09:35PM +0800, Jia He wrote: > 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 > v12: > refine PATCH 01, remove the !! since C languages can convert unsigned > to bool (Catalin) Thanks. I think it's a bit late to take something like this for 5.4 now, especially as the current behaviour has always been there. Hopefully somebody can queue it for 5.5 instead. Will
[PATCH v12 0/4] fix double page fault in cow_user_page for pfn mapping
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 v12: refine PATCH 01, remove the !! since C languages can convert unsigned to bool (Catalin) v11: refine cpu_has_hw_af in PATCH 01(Will Deacon, Suzuki) change the default return value to true in arch_faults_on_old_pte add PATCH 03 for overriding arch_faults_on_old_pte(false) on x86 v10: add r-b from Catalin and a-b from Kirill in PATCH 03 remoe Reported-by in PATCH 01 v9: refactor cow_user_page for indention optimization (Catalin) hold the ptl longer (Catalin) 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 (4): arm64: cpufeature: introduce helper cpu_has_hw_af() arm64: mm: implement arch_faults_on_old_pte() on arm64 x86/mm: implement arch_faults_on_old_pte() stub on x86 mm: fix double page fault on arm64 if PTE_AF is cleared arch/arm64/include/asm/cpufeature.h | 14 arch/arm64/include/asm/pgtable.h| 14 arch/x86/include/asm/pgtable.h | 6 ++ mm/memory.c | 104 4 files changed, 123 insertions(+), 15 deletions(-) -- 2.17.1
