pagemap: set pagemap walk limit to PMD boundary

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 <[email protected]>
Cc: Jun'ichi Nomura <[email protected]>
Acked-by: KAMEZAWA Hiroyuki <[email protected]>
Cc: Matt Mackall <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

0 files changed, 0 insertions, 0 deletions