linux-kernel - Re: [PATCH 12/12] xen/mtrr: Add mtrr

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Message-ID: <4CA231A8.5000100@zytor.com>
Date:	Tue, 28 Sep 2010 11:19:20 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Stefano Stabellini <stefano.stabellini@...citrix.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"xen-devel@...ts.xensource.com" <xen-devel@...ts.xensource.com>,
	Jeremy Fitzhardinge <Jeremy.Fitzhardinge@...rix.com>,
	"sct@...hat.com" <sct@...hat.com>
Subject: Re: [PATCH 12/12] xen/mtrr: Add mtrr_if support for Xen mtrr

On 09/28/2010 11:13 AM, Jeremy Fitzhardinge wrote:
>  On 09/28/2010 10:56 AM, H. Peter Anvin wrote:
>> On 09/28/2010 10:13 AM, Jeremy Fitzhardinge wrote:
>>> Yes, we could just mask out the MTRR CPU feature and rely entirely on PAT.
>>>
>>> The alternative would be to use the wrmsr hooks to emulate the Intel
>>> MTRR registers by mapping them to hypercalls, but that seems needlessly
>>> complex.
>>>
>> Indeed.  Relying on pure PAT is the Right Thing[TM].
> 
> Is there a plan to formally deprecate /proc/mtrr and the kernel
> infrastructure behind it?
> 

No, and we really can't do it for a couple of reasons:

a) Pre-PAT hardware;
b) MTRRs and PAT interact on hardware;
c) MTRRs, but not PAT, interact with SMM.

However, since a virtual machine like Xen doesn't have these issues, it
doesn't apply.

	-hpa
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