[PATCH] x86/pkeys: Update documentation

From: Dave Hansen
Date: Tue Oct 04 2016 - 12:39:17 EST

From: Dave Hansen <dave.hansen@xxxxxxxxx>

There are a few items that have gotten stale in the protection
keys documentation. The config option description only applied
to the execute-only support and is not accurate for the current
code. There was also a typo with the number of system calls. I
also wanted to call out that pkey_set() is not a kernel-provided
facility, and where to find an implementation.

Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: x86@xxxxxxxxxx
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx

b/Documentation/x86/protection-keys.txt | 14 +++++---------
1 file changed, 5 insertions(+), 9 deletions(-)

diff -puN Documentation/x86/protection-keys.txt~pkeys-docfix Documentation/x86/protection-keys.txt
--- a/Documentation/x86/protection-keys.txt~pkeys-docfix 2016-10-04 09:31:01.361928429 -0700
+++ b/Documentation/x86/protection-keys.txt 2016-10-04 09:32:39.142383585 -0700
@@ -20,7 +20,7 @@ instruction fetches.

=========================== Syscalls ===========================

-There are 2 system calls which directly interact with pkeys:
+There are 3 system calls which directly interact with pkeys:

int pkey_alloc(unsigned long flags, unsigned long init_access_rights)
int pkey_free(int pkey);
@@ -52,6 +52,10 @@ is no longer in use:
munmap(ptr, PAGE_SIZE);

+(Note: pkey_set() is a wrapper for the RDPKRU and WRPKRU instructions.
+ An example implementation can be found in
+ tools/testing/selftests/x86/protection_keys.c)
=========================== Behavior ===========================

The kernel attempts to make protection keys consistent with the
@@ -79,11 +83,3 @@ with a read():
The kernel will send a SIGSEGV in both cases, but si_code will be set
to SEGV_PKERR when violating protection keys versus SEGV_ACCERR when
the plain mprotect() permissions are violated.
-=========================== Config Option ===========================
-This config option adds approximately 1.5kb of text. and 50 bytes of
-data to the executable. A workload which does large O_DIRECT reads
-of holes in XFS files was run to exercise get_user_pages_fast(). No
-performance delta was observed with the config option
-enabled or disabled.