Commit-ID: 591b1d8d86074ac3a3163d89bcfe7b232cf83902 Gitweb: http://git.kernel.org/tip/591b1d8d86074ac3a3163d89bcfe7b232cf83902 Author: Dave Hansen <[email protected]> AuthorDate: Mon, 14 Dec 2015 11:06:34 -0800 Committer: Ingo Molnar <[email protected]> CommitDate: Tue, 29 Mar 2016 11:21:17 +0200
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 <[email protected]> Signed-off-by: Dave Hansen <[email protected]> Cc: Andy Lutomirski <[email protected]> Cc: Borislav Petkov <[email protected]> Cc: Brian Gerst <[email protected]> Cc: Dave Hansen <[email protected]> Cc: Denys Vlasenko <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Link: http://lkml.kernel.org/r/[email protected] [ Added changelog. ] Signed-off-by: Ingo Molnar <[email protected]> Signed-off-by: Ingo Molnar <[email protected]> --- Documentation/x86/protection-keys.txt | 27 +++++++++++++++++++++++++++ 1 file changed, 27 insertions(+) diff --git a/Documentation/x86/protection-keys.txt b/Documentation/x86/protection-keys.txt new file mode 100644 index 0000000..c281ded --- /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.
