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authorLinus Torvalds <torvalds@linux-foundation.org>2016-04-14 19:53:46 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-04-14 19:53:46 -0700
commit806fdcce017dc98c4dbf8ed001750a0d7d2bb0af (patch)
tree9cf2e221546d26219e5f83fff40f5be6e545f377 /Documentation
parenta1f983174dd7e535e50ca850fcfb3b8d38149f39 (diff)
parenta3125494cff084b098c80bb36fbe2061ffed9d52 (diff)
Merge branch 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull x86 fixes from Ingo Molnar: "Misc fixes: a binutils fix, an lguest fix, an mcelog fix and a missing documentation fix" * 'x86-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: x86/mce: Avoid using object after free in genpool lguest, x86/entry/32: Fix handling of guest syscalls using interrupt gates x86/build: Build compressed x86 kernels as PIE x86/mm/pkeys: Add missing Documentation
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+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.