From: Adam Litke <agl@us.ibm.com>
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.
Signed-off-by: Adam Litke <agl@us.ibm.com>
Cc: <linux-mm@kvack.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---
arch/i386/mm/hugetlbpage.c | 13 +++++++++++--
mm/hugetlb.c | 2 --
2 files changed, 11 insertions(+), 4 deletions(-)
diff -puN arch/i386/mm/hugetlbpage.c~hugetlb-move-stale-pte-check-into-huge_pte_alloc arch/i386/mm/hugetlbpage.c
--- 25/arch/i386/mm/hugetlbpage.c~hugetlb-move-stale-pte-check-into-huge_pte_alloc Mon Aug 29 15:48:03 2005
+++ 25-akpm/arch/i386/mm/hugetlbpage.c Mon Aug 29 15:48:03 2005
@@ -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 -puN mm/hugetlb.c~hugetlb-move-stale-pte-check-into-huge_pte_alloc mm/hugetlb.c
--- 25/mm/hugetlb.c~hugetlb-move-stale-pte-check-into-huge_pte_alloc Mon Aug 29 15:48:03 2005
+++ 25-akpm/mm/hugetlb.c Mon Aug 29 15:48:03 2005
@@ -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));
_