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@xxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Jun'ichi Nomura <j-nomura@xxxxxxxxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Matt Mackall <mpm@xxxxxxxxxxx>
---
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;
--
1.7.2.3
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