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From: Toshi Kani <toshi.kani@hpe.com>
To: Borislav Petkov <bp@suse.de>
Cc: jgross@suse.com, mcgrof@suse.com, x86@kernel.org,
	linux-kernel@vger.kernel.org, paul.gortmaker@windriver.com,
	hpa@zytor.com, xen-devel@lists.xenproject.org,
	tglx@linutronix.de, mingo@kernel.org, elliott@hpe.com
Subject: Re: [PATCH v2 1/6] x86/mm/pat: Change PAT to support non-default PAT MSR
Date: Tue, 22 Mar 2016 12:35:19 -0600	[thread overview]
Message-ID: <1458671719.6393.565.camel@hpe.com> (raw)
In-Reply-To: <20160322165725.GB5656@pd.tnic>

On Tue, 2016-03-22 at 17:57 +0100, Borislav Petkov wrote:
> $Subject is misleading - there's no non-default PAT MSR - the setting is
> non-default.

Right.  Will change to "Add support of non-default PAT MSR setting at
handoff".

> On Wed, Mar 16, 2016 at 06:44:57PM -0600, Toshi Kani wrote:
> > In preparation to fix a regression caused by 'commit 9cd25aac1f44
> > ("x86/mm/pat: Emulate PAT when it is disabled")', PAT needs to
> > support a case that PAT MSR is initialized with a non-default
> > value.
> > 
> > When pat_init() is called in PAT disable state, it initializes
> 
> 		  is called and PAT is disabled

Will do.

> > PAT table with the BIOS default value. Xen, however, sets PAT MSR
> > with a non-default value to enable WC. This causes inconsistency
> > between PAT table and PAT MSR when PAT is set to disable on Xen.
> > 
> > Change pat_init() to handle the PAT disable cases properly.  Add
> > pat_keep_handoff_state() to handle two cases when PAT is set to
> > disable.
> >  1. CPU supports PAT: Set PAT table to be consistent with PAT MSR.
> >  2. CPU does not support PAT: Set PAT table to be consistent with
> >     PWT and PCD bits in a PTE.
> > 
 :
> > +/**
> > + * pat_keep_handoff_state - Set PAT table to the handoff state
> > + *
> > + * This function keeps PAT in the BIOS handoff state. When CPU
> > supports
> > + * PAT, it sets PAT table to be consistent with PAT MSR. When CPU does
> > not
> > + * support PAT, it emulates PAT by setting PAT table consistent with
> > PWT
> > + * and PCD bits in a PTE.
> > + *
> > + * The PAT table is global to all CPUs, which is initialized once at
> > + * boot-time. Any subsequent calls to this function have no effect.
> > + */
> > +static void pat_keep_handoff_state(void)
> 
> Static function, no need for "pat_" prefix. Also, no need for the
> kernel-doc comment.
> 
> Also, no need for all that handoff nomenclature etc, just call it
> setup_pat(). Because it does exactly that - it sets up the PAT bits
> unconditionally, regardless of enabled or not.

I'd like to make it clear that this function does not set PAT MSR, unlike
what pat_init() does.  When CPU supports PAT, it keeps PAT MSR in whatever
the setting at handoff, and initializes PAT table to match with this
setting.

I am open to a better name, but I am afraid that setup_pat() can be
confusing as if it sets PAT MSR.

> >  {
> > -	u64 pat;
> > -	struct cpuinfo_x86 *c = &boot_cpu_data;
> > +	u64 pat = 0;
> > +	static int set_handoff_done;
> 
> s/set_handoff_done/pat_setup_done/

I will match it with a func name once we decided.

Thanks,
-Toshi

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  parent reply	other threads:[~2016-03-22 18:20 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <1458175502-31936-1-git-send-email-toshi.kani@hpe.com>
2016-03-17  0:44 ` Toshi Kani
     [not found] ` <1458175502-31936-2-git-send-email-toshi.kani@hpe.com>
2016-03-22 16:57   ` Borislav Petkov
     [not found]   ` <20160322165725.GB5656@pd.tnic>
2016-03-22 18:35     ` Toshi Kani [this message]
2016-03-23  8:43       ` Borislav Petkov
2016-03-23 15:46         ` Toshi Kani
2016-03-22 19:17     ` Thomas Gleixner

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