Patch "x86/pat: Document the PAT initialization sequence" has been added to the 4.4-stable tree

Patch "x86/pat: Document the PAT initialization sequence" has been added to the 4.4-stable tree

[gregkh]

This is a note to let you know that I've just added the patch titled

    x86/pat: Document the PAT initialization sequence

to the 4.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-pat-document-the-pat-initialization-sequence.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From b6350c21cfe8aa9d65e189509a23c0ea4b8362c2 Mon Sep 17 00:00:00 2001
From: Toshi Kani <toshi.kani@hpe.com>
Date: Wed, 23 Mar 2016 15:42:03 -0600
Subject: x86/pat: Document the PAT initialization sequence

From: Toshi Kani <toshi.kani@hpe.com>

commit b6350c21cfe8aa9d65e189509a23c0ea4b8362c2 upstream.

Update PAT documentation to describe how PAT is initialized under
various configurations.

Signed-off-by: Toshi Kani <toshi.kani@hpe.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bp@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Luis R. Rodriguez <mcgrof@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Toshi Kani <toshi.kani@hp.com>
Cc: elliott@hpe.com
Cc: konrad.wilk@oracle.com
Cc: paul.gortmaker@windriver.com
Cc: xen-devel@lists.xenproject.org
Link: http://lkml.kernel.org/r/1458769323-24491-8-git-send-email-toshi.kani@hpe.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 Documentation/x86/pat.txt |   32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

--- a/Documentation/x86/pat.txt
+++ b/Documentation/x86/pat.txt
@@ -196,3 +196,35 @@ Another, more verbose way of getting PAT
 "debugpat" boot parameter. With this parameter, various debug messages are
 printed to dmesg log.
 
+PAT Initialization
+------------------
+
+The following table describes how PAT is initialized under various
+configurations. The PAT MSR must be updated by Linux in order to support WC
+and WT attributes. Otherwise, the PAT MSR has the value programmed in it
+by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests.
+
+ MTRR PAT   Call Sequence               PAT State  PAT MSR
+ =========================================================
+ E    E     MTRR -> PAT init            Enabled    OS
+ E    D     MTRR -> PAT init            Disabled    -
+ D    E     MTRR -> PAT disable         Disabled   BIOS
+ D    D     MTRR -> PAT disable         Disabled    -
+ -    np/E  PAT  -> PAT disable         Disabled   BIOS
+ -    np/D  PAT  -> PAT disable         Disabled    -
+ E    !P/E  MTRR -> PAT init            Disabled   BIOS
+ D    !P/E  MTRR -> PAT disable         Disabled   BIOS
+ !M   !P/E  MTRR stub -> PAT disable    Disabled   BIOS
+
+ Legend
+ ------------------------------------------------
+ E         Feature enabled in CPU
+ D	   Feature disabled/unsupported in CPU
+ np	   "nopat" boot option specified
+ !P	   CONFIG_X86_PAT option unset
+ !M	   CONFIG_MTRR option unset
+ Enabled   PAT state set to enabled
+ Disabled  PAT state set to disabled
+ OS        PAT initializes PAT MSR with OS setting
+ BIOS      PAT keeps PAT MSR with BIOS setting
+


Patches currently in stable-queue which might be from toshi.kani@hpe.com are

queue-4.4/x86-mm-pat-replace-cpu_has_pat-with-boot_cpu_has.patch
queue-4.4/x86-mtrr-fix-xorg-crashes-in-qemu-sessions.patch
queue-4.4/x86-mm-pat-add-support-of-non-default-pat-msr-setting.patch
queue-4.4/x86-xen-pat-remove-pat-table-init-code-from-xen.patch
queue-4.4/x86-mtrr-fix-pat-init-handling-when-mtrr-is-disabled.patch
queue-4.4/x86-mm-pat-add-pat_disable-interface.patch
queue-4.4/x86-mm-pat-fix-bug_on-in-mmap_mem-on-qemu-i386.patch
queue-4.4/x86-pat-document-the-pat-initialization-sequence.patch