linux-kernel - [tip: x86/mm] Documentation/protection-keys: Clean up documentation for User Space pkeys

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Message-ID: <165464339351.4207.13791430848488231130.tip-bot2@tip-bot2>
Date:   Tue, 07 Jun 2022 23:09:53 -0000
From:   "tip-bot2 for Ira Weiny" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Ira Weiny <ira.weiny@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/mm] Documentation/protection-keys: Clean up documentation
 for User Space pkeys

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@...el.com>
AuthorDate:    Tue, 19 Apr 2022 10:06:06 -07:00
Committer:     Dave Hansen <dave.hansen@...ux.intel.com>
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@...el.com>
Signed-off-by: Dave Hansen <dave.hansen@...ux.intel.com>
Link: https://lkml.kernel.org/r/20220419170649.1022246-2-ira.weiny@intel.com
---
 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
 ========