Messages in this thread Patch in this message | | | From | "Kirill A. Shutemov" <> | Subject | [PATCHv4 10/12] mm: Do not lose dirty and access bits in pmdp_invalidate() | Date | Wed, 13 Dec 2017 13:57:54 +0300 |
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Vlastimil noted that pmdp_invalidate() is not atomic and we can lose dirty and access bits if CPU sets them after pmdp dereference, but before set_pmd_at().
The patch change pmdp_invalidate() to make the entry non-present atomically and return previous value of the entry. This value can be used to check if CPU set dirty/accessed bits under us.
The race window is very small and I haven't seen any reports that can be attributed to the bug. For this reason, I don't think backporting to stable trees needed.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Reported-by: Vlastimil Babka <vbabka@suse.cz> Cc: Hugh Dickins <hughd@google.com> --- include/asm-generic/pgtable.h | 2 +- mm/pgtable-generic.c | 6 +++--- 2 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h index ae83b14200b8..f449c71cbdc0 100644 --- a/include/asm-generic/pgtable.h +++ b/include/asm-generic/pgtable.h @@ -325,7 +325,7 @@ static inline pmd_t generic_pmdp_establish(struct vm_area_struct *vma, #endif #ifndef __HAVE_ARCH_PMDP_INVALIDATE -extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, +extern pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp); #endif diff --git a/mm/pgtable-generic.c b/mm/pgtable-generic.c index 1e4ee763c190..cf2af04b34b9 100644 --- a/mm/pgtable-generic.c +++ b/mm/pgtable-generic.c @@ -181,12 +181,12 @@ pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp) #endif #ifndef __HAVE_ARCH_PMDP_INVALIDATE -void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, +pmd_t pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp) { - pmd_t entry = *pmdp; - set_pmd_at(vma->vm_mm, address, pmdp, pmd_mknotpresent(entry)); + pmd_t old = pmdp_establish(vma, address, pmdp, pmd_mknotpresent(*pmdp)); flush_pmd_tlb_range(vma, address, address + HPAGE_PMD_SIZE); + return old; } #endif -- 2.15.0
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