--- zzzz-none-000/linux-3.10.107/Documentation/vm/pagemap.txt	2017-06-27 09:49:32.000000000 +0000
+++ scorpion-7490-727/linux-3.10.107/Documentation/vm/pagemap.txt	2021-02-04 17:41:59.000000000 +0000
@@ -5,7 +5,7 @@
 userspace programs to examine the page tables and related information by
 reading files in /proc.
 
-There are three components to pagemap:
+There are four components to pagemap:
 
  * /proc/pid/pagemap.  This file lets a userspace process find out which
    physical frame each virtual page is mapped to.  It contains one 64-bit
@@ -15,11 +15,18 @@
     * Bits 0-54  page frame number (PFN) if present
     * Bits 0-4   swap type if swapped
     * Bits 5-54  swap offset if swapped
-    * Bits 55-60 page shift (page size = 1<<page shift)
-    * Bit  61    page is file-page or shared-anon
+    * Bit  55    pte is soft-dirty (see Documentation/vm/soft-dirty.txt)
+    * Bit  56    page exclusively mapped (since 4.2)
+    * Bits 57-60 zero
+    * 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
@@ -61,6 +68,13 @@
     20. NOPAGE
     21. KSM
     22. THP
+    23. BALLOON
+    24. ZERO_PAGE
+    25. IDLE
+
+ * /proc/kpagecgroup.  This file contains a 64-bit inode number of the
+   memory cgroup each page is charged to, indexed by PFN. Only available when
+   CONFIG_MEMCG is set.
 
 Short descriptions to the page flags:
 
@@ -101,6 +115,18 @@
 22. THP
     contiguous pages which construct transparent hugepages
 
+23. BALLOON
+    balloon compaction page
+
+24. ZERO_PAGE
+    zero page for pfn_zero or huge_zero page
+
+25. IDLE
+    page has not been accessed since it was marked idle (see
+    Documentation/vm/idle_page_tracking.txt). Note that this flag may be
+    stale in case the page was accessed via a PTE. To make sure the flag
+    is up-to-date one has to read /sys/kernel/mm/page_idle/bitmap first.
+
     [IO related page flags]
  1. ERROR     IO error occurred
  3. UPTODATE  page has up-to-date data
@@ -122,7 +148,8 @@
 13. SWAPCACHE   page is mapped to swap space, ie. has an associated swap entry
 14. SWAPBACKED  page is backed by swap/RAM
 
-The page-types tool in this directory can be used to query the above flags.
+The page-types tool in the tools/vm directory can be used to query the
+above flags.
 
 Using pagemap to do something useful:
 
@@ -147,5 +174,10 @@
 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 seeked an odd number of bytes
+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.