From: "Kirill A. Shutemov" kirill.shutemov@linux.intel.com
[ Upstream commit c58f0bb77ed8bf93dfdde762b01cb67eebbdfc29 ]
Patch series "Do not lose dirty bit on THP pages", v4.
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 bug can lead to data loss, but the race window is tiny and I haven't seen any reports that suggested that it happens in reality. So I don't think it worth sending it to stable.
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() that returns previous value.
If generic implementation of pmdp_invalidate() is used, architecture needs to provide atomic pmdp_estabish().
pmdp_estabish() is not used out-side generic implementation of pmdp_invalidate() so far, but I think this can change in the future.
This patch (of 12):
This is an implementation of pmdp_establish() that is only suitable for an architecture that doesn't have hardware dirty/accessed bits. In this case we can't race with CPU which sets these bits and non-atomic approach is fine.
Link: http://lkml.kernel.org/r/20171213105756.69879-2-kirill.shutemov@linux.intel.... Signed-off-by: Kirill A. Shutemov kirill.shutemov@linux.intel.com Cc: Vlastimil Babka vbabka@suse.cz Cc: Andrea Arcangeli aarcange@redhat.com Cc: Michal Hocko mhocko@kernel.org Cc: Aneesh Kumar K.V aneesh.kumar@linux.vnet.ibm.com Cc: Catalin Marinas catalin.marinas@arm.com Cc: David Daney david.daney@cavium.com Cc: David Miller davem@davemloft.net Cc: H. Peter Anvin hpa@zytor.com Cc: Hugh Dickins hughd@google.com Cc: Ingo Molnar mingo@kernel.org Cc: Martin Schwidefsky schwidefsky@de.ibm.com Cc: Nitin Gupta nitin.m.gupta@oracle.com Cc: Ralf Baechle ralf@linux-mips.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Vineet Gupta vgupta@synopsys.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- include/asm-generic/pgtable.h | 15 +++++++++++++++ 1 file changed, 15 insertions(+)
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h index 4814cf971048..25b793325b09 100644 --- a/include/asm-generic/pgtable.h +++ b/include/asm-generic/pgtable.h @@ -237,6 +237,21 @@ extern void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp, extern pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp); #endif
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE +/* + * This is an implementation of pmdp_establish() that is only suitable for an + * architecture that doesn't have hardware dirty/accessed bits. In this case we + * can't race with CPU which sets these bits and non-atomic aproach is fine. + */ +static inline pmd_t generic_pmdp_establish(struct vm_area_struct *vma, + unsigned long address, pmd_t *pmdp, pmd_t pmd) +{ + pmd_t old_pmd = *pmdp; + set_pmd_at(vma->vm_mm, address, pmdp, pmd); + return old_pmd; +} +#endif + #ifndef __HAVE_ARCH_PMDP_INVALIDATE extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address, pmd_t *pmdp);