[PATCH] docs: proc: document ProtectionKey in smaps

[Kevin Brodsky <kevin.brodsky@arm.com>]

The ProtectionKey entry was added in v4.9; back then it was
x86-specific, but it now lives in generic code and applies to all
architectures supporting pkeys (currently x86, power, arm64).

Time to document it: add a paragraph to proc.rst about the
ProtectionKey entry.

Reported-by: Yury Khrustalev <yury.khrustalev@arm.com>
Signed-off-by: Kevin Brodsky <kevin.brodsky@arm.com>
---
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: David Hildenbrand <david@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: linux-fsdevel@vger.kernel.org
Cc: linux-mm@kvack.org
---
 Documentation/filesystems/proc.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index b0c0d1b45b99..d673cad7dbe4 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -549,6 +549,10 @@ does not take into account swapped out page of underlying shmem objects.
 naturally aligned THP pages of any currently enabled size. 1 if true, 0
 otherwise.
 
+If both the kernel and the system support protection keys (pkeys),
+"ProtectionKey" indicates the memory protection key associated with the
+virtual memory area.
+
 "VmFlags" field deserves a separate description. This member represents the
 kernel flags associated with the particular virtual memory area in two letter
 encoded manner. The codes are the following:
-- 
2.51.2