Hi, Vlastimil noted that pmdp_invalidate() is not atomic and we can loose dirty and access bits if CPU sets them after pmdp dereference, but before set_pmd_at(). The bug doesn't lead to user-visible misbehaviour in current kernel, but fixing this would be critical for future work on THP: both huge-ext4 and THP swap out rely on proper dirty tracking. Unfortunately, there's no way to address the issue in a generic way. We need to fix all architectures that support THP one-by-one. All architectures that have THP supported have to provide atomic pmdp_invalidate(). If generic implementation of pmdp_invalidate() is used, architecture needs to provide atomic pmdp_mknonpresent(). I've fixed the issue for x86, but I need help with the rest. So far THP is supported on 8 architectures. Power and S390 already provides atomic pmdp_invalidate(). x86 is fixed by this patches, so 5 architectures left: - arc; - arm; - arm64; - mips; - sparc -- it has custom pmdp_invalidate(), but it's racy too; Please, help me with them. Kirill A. Shutemov (3): x86/mm: Provide pmdp_mknotpresent() helper mm: Do not loose dirty and access bits in pmdp_invalidate() mm, thp: Do not loose dirty bit in __split_huge_pmd_locked() arch/x86/include/asm/pgtable-3level.h | 17 +++++++++++++++++ arch/x86/include/asm/pgtable.h | 13 +++++++++++++ mm/huge_memory.c | 13 +++++++++---- mm/pgtable-generic.c | 3 +-- 4 files changed, 40 insertions(+), 6 deletions(-) -- 2.11.0
