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authorToshi Kani2016-03-23 16:42:03 -0500
committerGreg Kroah-Hartman2016-08-16 02:30:50 -0500
commite270fdc5237154293d0b58d85ee6584742f98aeb (patch)
treea3bfd2c49e4f5e9b1edf47fb39201152e11d37a2 /Documentation
parent26b340ea33f49af99449607c20c97fa3f499c5fa (diff)
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x86/pat: Document the PAT initialization sequence
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>
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/x86/pat.txt32
1 files changed, 32 insertions, 0 deletions
diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt
index 54944c71b819..2a4ee6302122 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
196"debugpat" boot parameter. With this parameter, various debug messages are 196"debugpat" boot parameter. With this parameter, various debug messages are
197printed to dmesg log. 197printed to dmesg log.
198 198
199PAT Initialization
200------------------
201
202The following table describes how PAT is initialized under various
203configurations. The PAT MSR must be updated by Linux in order to support WC
204and WT attributes. Otherwise, the PAT MSR has the value programmed in it
205by the firmware. Note, Xen enables WC attribute in the PAT MSR for guests.
206
207 MTRR PAT Call Sequence PAT State PAT MSR
208 =========================================================
209 E E MTRR -> PAT init Enabled OS
210 E D MTRR -> PAT init Disabled -
211 D E MTRR -> PAT disable Disabled BIOS
212 D D MTRR -> PAT disable Disabled -
213 - np/E PAT -> PAT disable Disabled BIOS
214 - np/D PAT -> PAT disable Disabled -
215 E !P/E MTRR -> PAT init Disabled BIOS
216 D !P/E MTRR -> PAT disable Disabled BIOS
217 !M !P/E MTRR stub -> PAT disable Disabled BIOS
218
219 Legend
220 ------------------------------------------------
221 E Feature enabled in CPU
222 D Feature disabled/unsupported in CPU
223 np "nopat" boot option specified
224 !P CONFIG_X86_PAT option unset
225 !M CONFIG_MTRR option unset
226 Enabled PAT state set to enabled
227 Disabled PAT state set to disabled
228 OS PAT initializes PAT MSR with OS setting
229 BIOS PAT keeps PAT MSR with BIOS setting
230