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SubjectRe: [BUGFIX][PATCH] pagemap: set pagemap walk limit to PMD boundary
On Fri, 19 Nov 2010 18:07:45 +0900
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> wrote:

> Currently one pagemap_read() call walks in PAGEMAP_WALK_SIZE bytes
> (== 512 pages.) But there is a corner case where walk_pmd_range()
> accidentally runs over a VMA associated with a hugetlbfs file.
>
> For example, when a process has mappings to VMAs as shown below:
>
> # cat /proc/<pid>/maps
> ...
> 3a58f6d000-3a58f72000 rw-p 00000000 00:00 0
> 7fbd51853000-7fbd51855000 rw-p 00000000 00:00 0
> 7fbd5186c000-7fbd5186e000 rw-p 00000000 00:00 0
> 7fbd51a00000-7fbd51c00000 rw-s 00000000 00:12 8614 /hugepages/test
>
> then pagemap_read() goes into walk_pmd_range() path and walks in the range
> 0x7fbd51853000-0x7fbd51a53000, but the hugetlbfs VMA should be handled
> by walk_hugetlb_range(). Otherwise PMD for the hugepage is considered bad
> and cleared, which causes undesirable results.
>
> This patch fixes it by separating pagemap walk range into one PMD.
>
> Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>
> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Matt Mackall <mpm@selenic.com>
> ---
> fs/proc/task_mmu.c | 3 ++-
> 1 files changed, 2 insertions(+), 1 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index da6b01d..c126c83 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -706,6 +706,7 @@ static int pagemap_hugetlb_range(pte_t *pte, unsigned long hmask,
> * skip over unmapped regions.
> */
> #define PAGEMAP_WALK_SIZE (PMD_SIZE)
> +#define PAGEMAP_WALK_MASK (PMD_MASK)
> static ssize_t pagemap_read(struct file *file, char __user *buf,
> size_t count, loff_t *ppos)
> {
> @@ -776,7 +777,7 @@ static ssize_t pagemap_read(struct file *file, char __user *buf,
> unsigned long end;
>
> pm.pos = 0;
> - end = start_vaddr + PAGEMAP_WALK_SIZE;
> + end = (start_vaddr + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK;
> /* overflow ? */
> if (end < start_vaddr || end > end_vaddr)
> end = end_vaddr;

Ack.

But ALIGN() can't be used ?

Thanks,
-Kame





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