proc: fix documentation and description of pagemap

Since bit 57 was exported for uffd-wp write-protected (commit
fb8e37f: "mm/pagemap: export uffd-wp protection information"),
fixing it can reduce some unnecessary confusion.

Link: https://lkml.kernel.org/r/[email protected]
Fixes: fb8e37f ("mm/pagemap: export uffd-wp protection information")
Signed-off-by: Yun Zhou <[email protected]>
Reviewed-by: Peter Xu <[email protected]>
Cc: Jonathan Corbet <[email protected]>
Cc: Tiberiu A Georgescu <[email protected]>
Cc: Florian Schmidt <[email protected]>
Cc: Ivan Teterevkov <[email protected]>
Cc: SeongJae Park <[email protected]>
Cc: Yang Shi <[email protected]>
Cc: David Hildenbrand <[email protected]>
Cc: Axel Rasmussen <[email protected]>
Cc: Miaohe Lin <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Colin Cross <[email protected]>
Cc: Alistair Popple <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: zhouyun1306

Documentation/admin-guide/mm/pagemap.rst

@@ -23,7 +23,7 @@ There are four components to pagemap:
     * Bit  56    page exclusively mapped (since 4.2)
     * Bit  57    pte is uffd-wp write-protected (since 5.13) (see
       :ref:`Documentation/admin-guide/mm/userfaultfd.rst <userfaultfd>`)
-    * Bits 57-60 zero
+    * Bits 58-60 zero
     * Bit  61    page is file-page or shared-anon (since 3.5)
     * Bit  62    page swapped
     * Bit  63    page present

fs/proc/task_mmu.c

@@ -1597,7 +1597,8 @@ static const struct mm_walk_ops pagemap_ops = {
  * Bits 5-54  swap offset if swapped
  * Bit  55    pte is soft-dirty (see Documentation/admin-guide/mm/soft-dirty.rst)
  * Bit  56    page exclusively mapped
- * Bits 57-60 zero
+ * Bit  57    pte is uffd-wp write-protected
+ * Bits 58-60 zero
  * Bit  61    page is file-page or shared-anon
  * Bit  62    page swapped
  * Bit  63    page present