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asm-generic: provide generic_pmdp_establish()
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.com 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>
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@ -309,6 +309,21 @@ extern void pgtable_trans_huge_deposit(struct mm_struct *mm, pmd_t *pmdp,
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extern pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp);
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extern pgtable_t pgtable_trans_huge_withdraw(struct mm_struct *mm, pmd_t *pmdp);
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#endif
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#endif
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#ifdef CONFIG_TRANSPARENT_HUGEPAGE
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/*
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* This is an implementation of pmdp_establish() that is only suitable for an
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* architecture that doesn't have hardware dirty/accessed bits. In this case we
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* can't race with CPU which sets these bits and non-atomic aproach is fine.
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*/
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static inline pmd_t generic_pmdp_establish(struct vm_area_struct *vma,
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unsigned long address, pmd_t *pmdp, pmd_t pmd)
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{
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pmd_t old_pmd = *pmdp;
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set_pmd_at(vma->vm_mm, address, pmdp, pmd);
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return old_pmd;
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}
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#endif
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#ifndef __HAVE_ARCH_PMDP_INVALIDATE
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#ifndef __HAVE_ARCH_PMDP_INVALIDATE
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extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
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extern void pmdp_invalidate(struct vm_area_struct *vma, unsigned long address,
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pmd_t *pmdp);
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pmd_t *pmdp);
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