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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 <dave.hansen@intel.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: linux-doc@vger.kernel.org
Cc: corbet@lwn.net
Link: http://lkml.kernel.org/r/20161004163857.71E0D6F6@viggo.jf.intel.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
hifive-unleashed-5.1
Dave Hansen 2016-10-04 09:38:57 -07:00 committed by Thomas Gleixner
parent ba6d018e3d
commit 6679dac513
1 changed files with 5 additions and 9 deletions
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14
Documentation/x86/protection-keys.txt
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@ -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.