The following commit has been merged into the x86/mm branch of tip: Commit-ID: f8c1d4ca55177326adad1fdc6bf602423a507542 Gitweb: https://git.kernel.org/tip/f8c1d4ca55177326adad1fdc6bf602423a507542 Author: Ira Weiny <ira.weiny@xxxxxxxxx> AuthorDate: Tue, 19 Apr 2022 10:06:06 -07:00 Committer: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> CommitterDate: Tue, 07 Jun 2022 16:06:22 -07:00 Documentation/protection-keys: Clean up documentation for User Space pkeys The documentation for user space pkeys was a bit dated including things such as Amazon and distribution testing information which is irrelevant now. Update the documentation. This also streamlines adding the Supervisor pkey documentation later on. Signed-off-by: Ira Weiny <ira.weiny@xxxxxxxxx> Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Link: https://lkml.kernel.org/r/20220419170649.1022246-2-ira.weiny@xxxxxxxxx --- Documentation/core-api/protection-keys.rst | 44 ++++++++++----------- 1 file changed, 21 insertions(+), 23 deletions(-) diff --git a/Documentation/core-api/protection-keys.rst b/Documentation/core-api/protection-keys.rst index ec575e7..bf28ac0 100644 --- a/Documentation/core-api/protection-keys.rst +++ b/Documentation/core-api/protection-keys.rst @@ -4,31 +4,29 @@ Memory Protection Keys ====================== -Memory Protection Keys for Userspace (PKU aka PKEYs) is a feature -which is found on Intel's Skylake (and later) "Scalable Processor" -Server CPUs. It will be available in future non-server Intel parts -and future AMD processors. - -For anyone wishing to test or use this feature, it is available in -Amazon's EC2 C5 instances and is known to work there using an Ubuntu -17.04 image. - -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 +Memory Protection Keys provide a mechanism for enforcing page-based +protections, but without requiring modification of the page tables when an +application changes protection domains. + +Pkeys Userspace (PKU) is a feature which can be found on: + * Intel server CPUs, Skylake and later + * Intel client CPUs, Tiger Lake (11th Gen Core) and later + * Future AMD CPUs + +Pkeys work by dedicating 4 previously Reserved bits in each page table entry to +a "protection key", giving 16 possible keys. + +Protections for each key are defined with a per-CPU user-accessible register +(PKRU). Each of these is a 32-bit register storing two bits (Access Disable +and Write Disable) for each of 16 keys. + +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. +There are two instructions (RDPKRU/WRPKRU) for reading and writing to the +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. Syscalls ========
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