linux-kernel - [PATCH] x86/pkeys: Update documentation

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Message-Id: <20161004163857.71E0D6F6@viggo.jf.intel.com>
Date:   Tue, 04 Oct 2016 09:38:57 -0700
From:   Dave Hansen <dave@...1.net>
To:     linux-kernel@...r.kernel.org
Cc:     Dave Hansen <dave@...1.net>, dave.hansen@...el.com, x86@...nel.org,
        corbet@....net, linux-doc@...r.kernel.org
Subject: [PATCH] x86/pkeys: Update documentation


From: Dave Hansen <dave.hansen@...el.com>

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@...el.com>
Cc: x86@...nel.org
Cc: Jonathan Corbet <corbet@....net>
Cc: linux-doc@...r.kernel.org
---

 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);
 	pkey_free(pkey);
 
+(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.
_