linux-kernel - Re: [PATCH v2 6/6] x86/pat: Document PAT initializations

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Date:	Tue, 22 Mar 2016 16:15:38 -0600
From:	Toshi Kani <toshi.kani@....com>
To:	Borislav Petkov <bp@...e.de>
Cc:	mingo@...nel.org, hpa@...or.com, tglx@...utronix.de,
	mcgrof@...e.com, jgross@...e.com, paul.gortmaker@...driver.com,
	konrad.wilk@...cle.com, elliott@....com, x86@...nel.org,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 6/6] x86/pat: Document PAT initializations

On Tue, 2016-03-22 at 18:02 +0100, Borislav Petkov wrote:
> On Wed, Mar 16, 2016 at 06:46:59PM -0600, Toshi Kani wrote:
> > Update PAT documentation to describe how PAT is initialized under
> > various configurations.
> > 
 :
> >  
> > +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
> 
> Err "PAT MSR must be updated by Linux in order to support WC and WT" ...
> or so?

Right. Will do.

> > +to support WC and WT attributes. Otherwise, PAT keeps PAT MSR value
> > set
> > +by BIOS.
> 
> "Otherwise, the PAT MSR has the value programmed in it by the firmware."

Will do.

> > 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
> 
> s/Enable/Enabled/

Will do.

> MTRR->pat_init() - either use function names for both or do pseudo like
> so:
> 
> MTRR init -> PAT init

OK, I will change all to pseudo.  MTRR has multiple caller functions, and
we do not have enough space to write them all.

> > + E    D     MTRR -> pat_init()          Disable    -
> 
> s/Disable/Disabled/. Ditto for the rest.

Will do.

> > + 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
> > +

Thanks,
-Toshi