|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
|=========================== 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.