The patch titled
Subject: pagemap: update documentation
has been added to the -mm tree. Its filename is
pagemap-update-documentation.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/pagemap-update-documentation.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/pagemap-update-documentation.patch
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*** Remember to use Documentation/SubmitChecklist when testing your code ***
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------------------------------------------------------
From: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Subject: pagemap: update documentation
Notes about recent changes.
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Cc: Mark Williamson <mwilliamson@xxxxxxxxxxxxxxxxx>
Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/vm/pagemap.txt | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
diff -puN Documentation/vm/pagemap.txt~pagemap-update-documentation Documentation/vm/pagemap.txt
--- a/Documentation/vm/pagemap.txt~pagemap-update-documentation
+++ a/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:
+ for unprivileged users from 4.0 till 4.2 open fails with -EPERM, starting
+ from from 4.2 PFN field is zeroed if user has no CAP_SYS_ADMIN capability.
+ 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.
_
Patches currently in -mm which might be from khlebnikov@xxxxxxxxxxxxxx are
mm-slub-fix-slab-double-free-in-case-of-duplicate-sysfs-filename.patch
pagemap-check-permissions-and-capabilities-at-open-time.patch
pagemap-switch-to-the-new-format-and-do-some-cleanup.patch
pagemap-rework-hugetlb-and-thp-report.patch
pagemap-hide-physical-addresses-from-non-privileged-users.patch
pagemap-add-mmap-exclusive-bit-for-marking-pages-mapped-only-here.patch
pagemap-add-mmap-exclusive-bit-for-marking-pages-mapped-only-here-fix.patch
pagemap-update-documentation.patch
linux-next.patch
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