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Subject[tip:mm/pkeys] x86/pkeys: Update documentation
Commit-ID:  6679dac513fd612f34d3a3d99d7b84ed6d5eb5cc
Author: Dave Hansen <>
AuthorDate: Tue, 4 Oct 2016 09:38:57 -0700
Committer: Thomas Gleixner <>
CommitDate: Wed, 5 Oct 2016 10:34:55 +0200

x86/pkeys: Update documentation

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 <>
Cc: Dave Hansen <>
Signed-off-by: Thomas Gleixner <>

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

diff --git a/Documentation/x86/protection-keys.txt b/Documentation/x86/protection-keys.txt
index 6da7689..b643045 100644
--- a/Documentation/x86/protection-keys.txt
+++ b/Documentation/x86/protection-keys.txt
@@ -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.
 \ /
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