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Subject[Resend] [Hugetlb x86] 2/3 Move stale pte check into huge_pte_alloc()
From
Date
Initial Post (Wed, 17 Aug 2005)

This patch moves the
if (! pte_none(*pte))
hugetlb_clean_stale_pgtable(pte);
logic into huge_pte_alloc() so all of its callers can be immune to the bug
described by Kenneth Chen at http://lkml.org/lkml/2004/6/16/246

> It turns out there is a bug in hugetlb_prefault(): with 3 level page table,
> huge_pte_alloc() might return a pmd that points to a PTE page. It happens
> if the virtual address for hugetlb mmap is recycled from previously used
> normal page mmap. free_pgtables() might not scrub the pmd entry on
> munmap and hugetlb_prefault skips on any pmd presence regardless what type
> it is.

Unless I am missing something, it seems more correct to place the check inside
huge_pte_alloc() to prevent a the same bug wherever a huge pte is allocated.
It also allows checking for this condition when lazily faulting huge pages
later in the series.

Diffed against 2.6.13-rc6

Signed-off-by: Adam Litke <agl@us.ibm.com>
---
arch/i386/mm/hugetlbpage.c | 13 +++++++++++--
mm/hugetlb.c | 2 --
2 files changed, 11 insertions(+), 4 deletions(-)
diff -upN reference/arch/i386/mm/hugetlbpage.c current/arch/i386/mm/hugetlbpage.c
--- reference/arch/i386/mm/hugetlbpage.c
+++ current/arch/i386/mm/hugetlbpage.c
@@ -22,12 +22,21 @@ pte_t *huge_pte_alloc(struct mm_struct *
{
pgd_t *pgd;
pud_t *pud;
- pmd_t *pmd = NULL;
+ pmd_t *pmd;
+ pte_t *pte = NULL;

pgd = pgd_offset(mm, addr);
pud = pud_alloc(mm, pgd, addr);
pmd = pmd_alloc(mm, pud, addr);
- return (pte_t *) pmd;
+
+ if (!pmd)
+ goto out;
+
+ pte = (pte_t *) pmd;
+ if (!pte_none(*pte) && !pte_huge(*pte))
+ hugetlb_clean_stale_pgtable(pte);
+out:
+ return pte;
}

pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr)
diff -upN reference/mm/hugetlb.c current/mm/hugetlb.c
--- reference/mm/hugetlb.c
+++ current/mm/hugetlb.c
@@ -360,8 +360,6 @@ int hugetlb_prefault(struct address_spac
ret = -ENOMEM;
goto out;
}
- if (! pte_none(*pte))
- hugetlb_clean_stale_pgtable(pte);

idx = ((addr - vma->vm_start) >> HPAGE_SHIFT)
+ (vma->vm_pgoff >> (HPAGE_SHIFT - PAGE_SHIFT));

-
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