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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>
28 lines
1.3 KiB
Plaintext
28 lines
1.3 KiB
Plaintext
Memory Protection Keys for Userspace (PKU aka PKEYs) is a CPU feature
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which will be found on future Intel CPUs.
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Memory Protection Keys provides a mechanism for enforcing page-based
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protections, but without requiring modification of the page tables
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when an application changes protection domains. It works by
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dedicating 4 previously ignored bits in each page table entry to a
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"protection key", giving 16 possible keys.
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There is also a new user-accessible register (PKRU) with two separate
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bits (Access Disable and Write Disable) for each key. Being a CPU
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register, PKRU is inherently thread-local, potentially giving each
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thread a different set of protections from every other thread.
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There are two new instructions (RDPKRU/WRPKRU) for reading and writing
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to the new register. The feature is only available in 64-bit mode,
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even though there is theoretically space in the PAE PTEs. These
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permissions are enforced on data access only and have no effect on
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instruction fetches.
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=========================== Config Option ===========================
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This config option adds approximately 1.5kb of text. and 50 bytes of
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data to the executable. A workload which does large O_DIRECT reads
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of holes in XFS files was run to exercise get_user_pages_fast(). No
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performance delta was observed with the config option
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enabled or disabled.
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