Update PAT documentation to describe how PAT is initialized under various configurations.
Signed-off-by: Toshi Kani <toshi.k...@hpe.com> Cc: Borislav Petkov <b...@suse.de> Cc: Luis R. Rodriguez <mcg...@suse.com> Cc: Juergen Gross <jgr...@suse.com> Cc: Ingo Molnar <mi...@kernel.org> Cc: H. Peter Anvin <h...@zytor.com> Cc: Thomas Gleixner <t...@linutronix.de> --- Documentation/x86/pat.txt | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) diff --git a/Documentation/x86/pat.txt b/Documentation/x86/pat.txt index 54944c7..f619e1d 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. PAT must be set to enable to initialize PAT MSR in order +to support WC and WT attributes. Otherwise, PAT keeps PAT MSR value set +by BIOS. Note, Xen enables WC attribute in BIOS setup for guests. + + MTRR PAT Call Sequence PAT State PAT MSR + ========================================================= + E E MTRR -> pat_init() Enable OS + E D MTRR -> pat_init() Disable - + D E MTRR -> pat_disable() Disable BIOS + D D MTRR -> pat_disable() Disable - + - np/E nopat() -> pat_disable() Disable BIOS + - np/D nopat() -> pat_disable() Disable - + E !P/E MTRR -> pat_init() Disable BIOS + D !P/E MTRR -> pat_disable() Disable BIOS + !M !P/E MTRR stub -> pat_disable() Disable 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 + Enable PAT state set to enable + Disable PAT state set to disable + OS PAT initializes PAT MSR with OS setup + BIOS PAT keeps PAT MSR with BIOS setup + _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
