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Date: Tue, 19 May 2009 16:55:06 +0200
From: Gerd Hoffmann <kraxel@redhat.com>
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To: Ingo Molnar <mingo@elte.hu>
CC: Jan Beulich <JBeulich@novell.com>, Jeremy Fitzhardinge <jeremy@goop.org>,
       Xen-devel <xen-devel@lists.xensource.com>,
       the arch/x86 maintainers <x86@kernel.org>,
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       "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
       Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [Xen-devel] Re: [GIT PULL] xen /proc/mtrr implementation
References: <20090518085902.GE10687@elte.hu> <4A11A3F8.1010202@goop.org> <20090519095918.GA11790@elte.hu> <4A12A46A02000078000017E1@vpn.id2.novell.com> <20090519110837.GA10548@elte.hu> <4A12A05C.6050004@redhat.com> <20090519122623.GD14305@elte.hu> <4A12B244.8070301@redhat.com> <20090519133138.GA8410@elte.hu> <4A12B97C.9040706@redhat.com> <20090519141708.GA6008@elte.hu>
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>>>> 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