The patch titled
Subject: asm-generic: provide generic_pmdp_establish()
has been added to the -mm tree. Its filename is
asm-generic-provide-generic_pmdp_establish.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/asm-generic-provide-generic_pmdp_establish.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/asm-generic-provide-generic_pmdp_establish.patch
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------------------------------------------------------
From: "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx>
Subject: 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@xxxxxxxxxxxxxxx
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Cc: Vlastimil Babka <vbabka@xxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxxxx>
Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: David Daney <david.daney@xxxxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Nitin Gupta <nitin.m.gupta@xxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Vineet Gupta <vgupta@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
include/asm-generic/pgtable.h | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff -puN include/asm-generic/pgtable.h~asm-generic-provide-generic_pmdp_establish include/asm-generic/pgtable.h
--- a/include/asm-generic/pgtable.h~asm-generic-provide-generic_pmdp_establish
+++ a/include/asm-generic/pgtable.h
@@ -309,6 +309,21 @@ extern void pgtable_trans_huge_deposit(s
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);
_
Patches currently in -mm which might be from kirill.shutemov@xxxxxxxxxxxxxxx are
asm-generic-provide-generic_pmdp_establish.patch
arc-use-generic_pmdp_establish-as-pmdp_establish.patch
arm-mm-provide-pmdp_establish-helper.patch
mips-use-generic_pmdp_establish-as-pmdp_establish.patch
x86-mm-provide-pmdp_establish-helper.patch
mm-do-not-lose-dirty-and-access-bits-in-pmdp_invalidate.patch
mm-use-updated-pmdp_invalidate-interface-to-track-dirty-accessed-bits.patch
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