linux-kernel - [PATCH V8 02/44] Documentation/protection-keys: Clean up documentation for User Space pkeys

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Message-Id: <20220127175505.851391-3-ira.weiny@intel.com>
Date:   Thu, 27 Jan 2022 09:54:23 -0800
From:   ira.weiny@...el.com
To:     Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     Ira Weiny <ira.weiny@...el.com>, Fenghua Yu <fenghua.yu@...el.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH V8 02/44] Documentation/protection-keys: Clean up documentation for User Space pkeys

From: Ira Weiny <ira.weiny@...el.com>

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>
---
 Documentation/core-api/protection-keys.rst | 43 ++++++++++------------
 1 file changed, 20 insertions(+), 23 deletions(-)

diff --git a/Documentation/core-api/protection-keys.rst b/Documentation/core-api/protection-keys.rst
index ec575e72d0b2..12331db474aa 100644
--- a/Documentation/core-api/protection-keys.rst
+++ b/Documentation/core-api/protection-keys.rst
@@ -4,31 +4,28 @@
 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 is found on Intel's Skylake "Scalable
+Processor" Server CPUs and later.  And it will be available in future
+non-server Intel parts and future AMD processors.
+
+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
 ========
-- 
2.31.1