linux-kernel - Re: [Xen-devel] Re: [GIT PULL] xen /proc/mtrr implementation

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Message-ID: <4A12C84A.5070100@redhat.com>
Date:	Tue, 19 May 2009 16:55:06 +0200
From:	Gerd Hoffmann <kraxel@...hat.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Jan Beulich <JBeulich@...ell.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [Xen-devel] Re: [GIT PULL] xen /proc/mtrr implementation

>>>> No, the linux kernel probably should do the wrmsr on one cpu only then.
>>> Why?

> | The change of MTRR's on _any_ of the guest CPUs in a dom0 context
> | should immediately be refected on all CPUs. Assymetric MTRR
> | settings are madness.

Exactly.  And thats why it is pointless to let the dom0 kernel write the 
mtrr msrs on more than one cpu.

>>>> Oops, the third "proper technical solutions" is missing.
>>> Yeah, the third one is to not touch MTRRs after bootup and use PAT.
>> Works only in case the CPU has PAT support.
>
> Which specific CPU without PAT support do you worry about?

For example:  I have a Notebook here, with MTRR and without PAT 
according to the boot log.  "Pentium III (Coppermine)" says /proc/cpuinfo.

cheers,
   Gerd
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