Commit 591b1d8d authored by Dave Hansen's avatar Dave Hansen Committed by Ingo Molnar

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: default avatarStefan Richter <>
Signed-off-by: default avatarDave Hansen <>
Cc: Andy Lutomirski <>
Cc: Borislav Petkov <>
Cc: Brian Gerst <>
Cc: Dave Hansen <>
Cc: Denys Vlasenko <>
Cc: H. Peter Anvin <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Thomas Gleixner <>
[ Added changelog. ]
Signed-off-by: default avatarIngo Molnar <>
Signed-off-by: default avatarIngo Molnar <>
parent 34a4cceb
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.
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