diff options
| author | Konstantin Khlebnikov | 2015-09-08 15:00:13 -0700 |
|---|---|---|
| committer | Linus Torvalds | 2015-09-08 15:35:28 -0700 |
| commit | 83b4b0bb635eee2b8e075062e4e008d1bc110ed7 (patch) | |
| tree | 032136b51f1ae668b08cd2f1583fbfe8a42f2939 /Documentation/vm | |
| parent | 77bb499bb60f4b79cca7d139c8041662860fcf87 (diff) | |
pagemap: update documentation
Notes about recent changes.
[akpm@linux-foundation.org: various tweaks]
Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Cc: Mark Williamson <mwilliamson@undo-software.com>
Cc: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'Documentation/vm')
| -rw-r--r-- | Documentation/vm/pagemap.txt | 14 |
1 files changed, 12 insertions, 2 deletions
diff --git a/Documentation/vm/pagemap.txt b/Documentation/vm/pagemap.txt index 56faec0f73f7..3cd38438242a 100644 --- a/Documentation/vm/pagemap.txt +++ b/Documentation/vm/pagemap.txt @@ -16,12 +16,17 @@ There are three components to pagemap: * Bits 0-4 swap type if swapped * Bits 5-54 swap offset if swapped * Bit 55 pte is soft-dirty (see Documentation/vm/soft-dirty.txt) - * Bit 56 page exclusively mapped + * Bit 56 page exclusively mapped (since 4.2) * Bits 57-60 zero - * Bit 61 page is file-page or shared-anon + * Bit 61 page is file-page or shared-anon (since 3.5) * Bit 62 page swapped * Bit 63 page present + Since Linux 4.0 only users with the CAP_SYS_ADMIN capability can get PFNs. + In 4.0 and 4.1 opens by unprivileged fail with -EPERM. Starting from + 4.2 the PFN field is zeroed if the user does not have CAP_SYS_ADMIN. + Reason: information about PFNs helps in exploiting Rowhammer vulnerability. + If the page is not present but in swap, then the PFN contains an encoding of the swap file number and the page's offset into the swap. Unmapped pages return a null PFN. This allows determining @@ -160,3 +165,8 @@ Other notes: Reading from any of the files will return -EINVAL if you are not starting the read on an 8-byte boundary (e.g., if you sought an odd number of bytes into the file), or if the size of the read is not a multiple of 8 bytes. + +Before Linux 3.11 pagemap bits 55-60 were used for "page-shift" (which is +always 12 at most architectures). Since Linux 3.11 their meaning changes +after first clear of soft-dirty bits. Since Linux 4.2 they are used for +flags unconditionally. |