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Commit 6679dac5 authored by Dave Hansen's avatar Dave Hansen Committed by Thomas Gleixner
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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: default avatarDave 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: default avatarThomas Gleixner <tglx@linutronix.de>
parent ba6d018e

Documentation/x86/protection-keys.txt

+5 −9
Original line number Diff line number Diff line
@@ -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.