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

To: Ingo Molnar <mingo@xxxxxxx>
Subject: Re: [Xen-devel] Re: [GIT PULL] xen /proc/mtrr implementation
From: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Date: Tue, 19 May 2009 16:55:06 +0200
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, the arch/x86 maintainers <x86@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jesse Barnes <jbarnes@xxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>, "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>
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No, the linux kernel probably should do the wrmsr on one cpu only then.

| 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.


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