On 09/17/2013 10:22 PM, Vlastimil Babka wrote:
> The function __munlock_pagevec_fill() introduced in commit 7a8010cd3
> ("mm: munlock: manual pte walk in fast path instead of follow_page_mask()")
> uses pmd_addr_end() for restricting its operation within current page table.
> This is insufficient on architectures/configurations where pmd is folded
> and pmd_addr_end() just returns the end of the full range to be walked. In
> this case, it allows pte++ to walk off the end of a page table resulting in
> unpredictable behaviour.
>
> This patch fixes the function by using pgd_addr_end() and pud_addr_end()
> before pmd_addr_end(), which will yield correct page table boundary on all
> configurations. This is similar to what existing page walkers do when walking
> each level of the page table.
>
> Additionaly, the patch clarifies a comment for get_locked_pte() call in the
> function.
>
> Reported-by: Fengguang Wu <fengguang...@intel.com>
> Cc: Jörn Engel <jo...@logfs.org>
> Cc: Mel Gorman <mgor...@suse.de>
> Cc: Michel Lespinasse <wal...@google.com>
> Cc: Hugh Dickins <hu...@google.com>
> Cc: Rik van Riel <r...@redhat.com>
> Cc: Johannes Weiner <han...@cmpxchg.org>
> Cc: Michal Hocko <mho...@suse.cz>
> Cc: Vlastimil Babka <vba...@suse.cz>
> Signed-off-by: Vlastimil Babka <vba...@suse.cz>
> ---
> mm/mlock.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> diff --git a/mm/mlock.c b/mm/mlock.c
> index d638026..758c0fc 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -379,10 +379,14 @@ static unsigned long __munlock_pagevec_fill(struct
> pagevec *pvec,
>
> /*
> * Initialize pte walk starting at the already pinned page where we
> - * are sure that there is a pte.
> + * are sure that there is a pte, as it was pinned under the same
> + * mmap_sem write op.
> */
> pte = get_locked_pte(vma->vm_mm, start, &ptl);
> - end = min(end, pmd_addr_end(start, end));
> + /* Make sure we do not cross the page table boundary */
> + end = pgd_addr_end(start, end);
> + end = pud_addr_end(start, end);
> + end = pmd_addr_end(start, end);
>
Nitpick, how about unfolding pmd_addr_end(start, end) directly? Like:
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -376,13 +376,14 @@ static unsigned long __munlock_pagevec_fill(struct
pagevec *pvec,
{
pte_t *pte;
spinlock_t *ptl;
+ unsigned long pmd_end = (start + PMD_SIZE) & PMD_MASK;
+ end = (pmd_end - 1 < end - 1) ? pmd_end : end;
/*
* Initialize pte walk starting at the already pinned page where we
* are sure that there is a pte.
*/
pte = get_locked_pte(vma->vm_mm, start, &ptl);
- end = min(end, pmd_addr_end(start, end));
/* The page next to the pinned page is the first we will try to
get */
start += PAGE_SIZE;
Anyway,
Reviewed-by: Bob Liu <bob....@oracle.com>
--
Regards,
-Bob
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