linux-kernel - Re: [PATCH 1/2] x86/mm/pat: Change pat

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Message-ID: <20160315154731.GD4559@pd.tnic>
Date:	Tue, 15 Mar 2016 16:47:31 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Toshi Kani <toshi.kani@....com>
Cc:	"Luis R. Rodriguez" <mcgrof@...nel.org>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"jgross@...e.com" <jgross@...e.com>,
	"paul.gortmaker@...driver.com" <paul.gortmaker@...driver.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
	"boris.ostrovsky@...cle.com" <boris.ostrovsky@...cle.com>
Subject: Re: [PATCH 1/2] x86/mm/pat: Change pat_disable() to emulate PAT table

On Tue, Mar 15, 2016 at 09:43:15AM -0600, Toshi Kani wrote:
> > Please use on init paths boot_cpu_has(X86_FEATURE_PAT) and on fast paths
> > static_cpu_has(X86_FEATURE_PAT). No more of that cpu_has_XXX ugliness.
> 
> 'cpu_has_pat' is defined as 'boot_cpu_has(X86_FEATURE_PAT)'.  Do you mean
> it should explicitly use 'boot_cpu_has(X86_FEATURE_PAT)'?

No, read what I said.

We use boot_cpu_has(<feature_bit>) on slow paths (i.e., init, bootup,
etc), where speed is not that important. static_cpu_has(<feature_bit>)
is an optimized version which should be used in hot paths.

-- 
Regards/Gruss,
    Boris.

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