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author | 2015-12-14 11:06:34 -0800 | |
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committer | 2016-03-29 11:21:17 +0200 | |
commit | 591b1d8d86074ac3a3163d89bcfe7b232cf83902 (patch) | |
tree | a2f7a1599cd7e4d60f28e20924ee5220761d67b1 | |
parent | x86/cpu: Add advanced power management bits (diff) | |
download | linux-591b1d8d86074ac3a3163d89bcfe7b232cf83902.tar.gz linux-591b1d8d86074ac3a3163d89bcfe7b232cf83902.tar.bz2 linux-591b1d8d86074ac3a3163d89bcfe7b232cf83902.zip |
x86/mm/pkeys: Add missing Documentation
Stefan Richter noticed that the X86_INTEL_MEMORY_PROTECTION_KEYS option
in arch/x86/Kconfig references Documentation/x86/protection-keys.txt,
but the file does not exist.
This is a patch merging mishap: the final (v8) version of the pkeys
series did not include the documentation patch 32 and v7 included.
Add it now.
Reported-by: Stefan Richter <stefanr@s5r6.in-berlin.de>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave@sr71.net>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20151214190634.426BEE41@viggo.jf.intel.com
[ Added changelog. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
-rw-r--r-- | Documentation/x86/protection-keys.txt | 27 |
1 files changed, 27 insertions, 0 deletions
diff --git a/Documentation/x86/protection-keys.txt b/Documentation/x86/protection-keys.txt new file mode 100644 index 000000000000..c281ded1ba16 --- /dev/null +++ b/Documentation/x86/protection-keys.txt @@ -0,0 +1,27 @@ +Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature +which will be found on future Intel CPUs. + +Memory Protection Keys provides a mechanism for enforcing page-based +protections, but without requiring modification of the page tables +when an application changes protection domains. It works by +dedicating 4 previously ignored bits in each page table entry to a +"protection key", giving 16 possible keys. + +There is also a new user-accessible register (PKRU) with two separate +bits (Access Disable and Write Disable) for each key. Being a CPU +register, PKRU is inherently thread-local, potentially giving each +thread a different set of protections from every other thread. + +There are two new instructions (RDPKRU/WRPKRU) for reading and writing +to the new register. The feature is only available in 64-bit mode, +even though there is theoretically space in the PAE PTEs. These +permissions are enforced on data access only and have no effect on +instruction fetches. + +=========================== 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. |