The patch titled
Subject: mm/hugetlb: pmd_huge() returns true for non-present hugepage
has been added to the -mm tree. Its filename is
mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage.patch
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------------------------------------------------------
From: Naoya Horiguchi <[email protected]>
Subject: mm/hugetlb: pmd_huge() returns true for non-present hugepage
Migrating hugepages and hwpoisoned hugepages are considered as non-present
hugepages, and they are referenced via migration entries and hwpoison
entries in their page table slots.
This behavior causes race condition because pmd_huge() doesn't tell
non-huge pages from migrating/hwpoisoned hugepages. follow_page_mask() is
one example where the kernel would call follow_page_pte() for such
hugepage while this function is supposed to handle only normal pages.
To avoid this, this patch makes pmd_huge() return true when pmd_none() is
true *and* pmd_present() is false. We don't have to worry about mixing up
non-present pmd entry with normal pmd (pointing to leaf level pte entry)
because pmd_present() is true in normal pmd.
The same race condition could happen in (x86-specific) gup_pmd_range(),
where this patch simply adds pmd_present() check instead of pmd_huge().
This is because gup_pmd_range() is fast path. If we have non-present
hugepage in this function, we will go into gup_huge_pmd(), then return 0
at flag mask check, and finally fall back to the slow path.
Fixes: 290408d4a2 ("hugetlb: hugepage migration core")
Signed-off-by: Naoya Horiguchi <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: James Hogan <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Michal Hocko <[email protected]>
Cc: Rik van Riel <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Luiz Capitulino <[email protected]>
Cc: Nishanth Aravamudan <[email protected]>
Cc: Lee Schermerhorn <[email protected]>
Cc: Steve Capper <[email protected]>
Cc: <[email protected]> [2.6.36+]
Signed-off-by: Andrew Morton <[email protected]>
---
arch/x86/mm/gup.c | 2 +-
arch/x86/mm/hugetlbpage.c | 8 +++++++-
mm/hugetlb.c | 2 ++
3 files changed, 10 insertions(+), 2 deletions(-)
diff -puN
arch/x86/mm/gup.c~mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage
arch/x86/mm/gup.c
---
a/arch/x86/mm/gup.c~mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage
+++ a/arch/x86/mm/gup.c
@@ -172,7 +172,7 @@ static int gup_pmd_range(pud_t pud, unsi
*/
if (pmd_none(pmd) || pmd_trans_splitting(pmd))
return 0;
- if (unlikely(pmd_large(pmd))) {
+ if (unlikely(pmd_large(pmd) || !pmd_present(pmd))) {
/*
* NUMA hinting faults need to be handled in the GUP
* slowpath for accounting purposes and so that they
diff -puN
arch/x86/mm/hugetlbpage.c~mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage
arch/x86/mm/hugetlbpage.c
---
a/arch/x86/mm/hugetlbpage.c~mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage
+++ a/arch/x86/mm/hugetlbpage.c
@@ -54,9 +54,15 @@ int pud_huge(pud_t pud)
#else
+/*
+ * pmd_huge() returns 1 if @pmd is hugetlb related entry, that is normal
+ * hugetlb entry or non-present (migration or hwpoisoned) hugetlb entry.
+ * Otherwise, returns 0.
+ */
int pmd_huge(pmd_t pmd)
{
- return !!(pmd_val(pmd) & _PAGE_PSE);
+ return !pmd_none(pmd) &&
+ (pmd_val(pmd) & (_PAGE_PRESENT|_PAGE_PSE)) != _PAGE_PRESENT;
}
int pud_huge(pud_t pud)
diff -puN
mm/hugetlb.c~mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage
mm/hugetlb.c
--- a/mm/hugetlb.c~mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage
+++ a/mm/hugetlb.c
@@ -3679,6 +3679,8 @@ follow_huge_pmd(struct mm_struct *mm, un
{
struct page *page;
+ if (!pmd_present(*pmd))
+ return NULL;
page = pte_page(*(pte_t *)pmd);
if (page)
page += ((address & ~PMD_MASK) >> PAGE_SHIFT);
_
Patches currently in -mm which might be from [email protected] are
mm-add-kpf_zero_page-flag-for-proc-kpageflags.patch
mm-hugetlb-reduce-arch-dependent-code-around-follow_huge_.patch
mm-hugetlb-pmd_huge-returns-true-for-non-present-hugepage.patch
mm-hugetlb-take-page-table-lock-in-follow_huge_pmd.patch
mm-hugetlb-fix-getting-refcount-0-page-in-hugetlb_fault.patch
mm-hugetlb-add-migration-hwpoisoned-entry-check-in-hugetlb_change_protection.patch
mm-hugetlb-add-migration-entry-check-in-__unmap_hugepage_range.patch
mm-hugetlb-fix-suboptimal-migration-hwpoisoned-entry-check.patch
mm-hugetlb-cleanup-and-rename-is_hugetlb_entry_migrationhwpoisoned.patch
do_shared_fault-check-that-mmap_sem-is-held.patch
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