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Date: Tue, 29 Mar 2016 03:40:23 -0700 From: tip-bot for Toshi Kani <tipbot@...or.com> To: linux-tip-commits@...r.kernel.org Cc: linux-kernel@...r.kernel.org, bp@...en8.de, hpa@...or.com, bp@...e.de, dvlasenk@...hat.com, mingo@...nel.org, brgerst@...il.com, toshi.kani@...com, akpm@...ux-foundation.org, torvalds@...ux-foundation.org, luto@...capital.net, peterz@...radead.org, tglx@...utronix.de, mcgrof@...e.com, toshi.kani@....com, jgross@...e.com Subject: [tip:x86/mm] x86/pat: Document the PAT initialization sequence Commit-ID: b6350c21cfe8aa9d65e189509a23c0ea4b8362c2 Gitweb: http://git.kernel.org/tip/b6350c21cfe8aa9d65e189509a23c0ea4b8362c2 Author: Toshi Kani <toshi.kani@....com> AuthorDate: Wed, 23 Mar 2016 15:42:03 -0600 Committer: Ingo Molnar <mingo@...nel.org> CommitDate: Tue, 29 Mar 2016 12:23:27 +0200 x86/pat: Document the PAT initialization sequence Update PAT documentation to describe how PAT is initialized under various configurations. Signed-off-by: Toshi Kani <toshi.kani@....com> Reviewed-by: Thomas Gleixner <tglx@...utronix.de> Cc: Andrew Morton <akpm@...ux-foundation.org> Cc: Andy Lutomirski <luto@...capital.net> Cc: Borislav Petkov <bp@...en8.de> Cc: Borislav Petkov <bp@...e.de> Cc: Brian Gerst <brgerst@...il.com> Cc: Denys Vlasenko <dvlasenk@...hat.com> Cc: H. Peter Anvin <hpa@...or.com> Cc: Juergen Gross <jgross@...e.com> Cc: Linus Torvalds <torvalds@...ux-foundation.org> Cc: Luis R. Rodriguez <mcgrof@...e.com> Cc: Peter Zijlstra <peterz@...radead.org> Cc: Toshi Kani <toshi.kani@...com> Cc: elliott@....com Cc: konrad.wilk@...cle.com Cc: paul.gortmaker@...driver.com Cc: xen-devel@...ts.xenproject.org Link: http://lkml.kernel.org/r/1458769323-24491-8-git-send-email-toshi.kani@hpe.com Signed-off-by: Ingo Molnar <mingo@...nel.org> --- Documentation/x86/pat.txt | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt index 54944c7..2a4ee63 100644 --- a/Documentation/x86/pat.txt +++ b/Documentation/x86/pat.txt @@ -196,3 +196,35 @@ Another, more verbose way of getting PAT related debug messages is with "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 +
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