linux-kernel - Re: [PATCH] X86: don't print a warning when MTRR are blank and running in KVM

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Date:	Fri, 22 Feb 2008 12:15:18 +0100
From:	"Joerg Roedel" <joerg.roedel@....com>
To:	"Ingo Molnar" <mingo@...e.hu>
cc:	"H. Peter Anvin" <hpa@...or.com>, tglx@...utronix.de,
	mingo@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] X86: don't print a warning when MTRR are blank and
 running in KVM

On Fri, Feb 22, 2008 at 11:00:44AM +0100, Ingo Molnar wrote:
> 
> * H. Peter Anvin <hpa@...or.com> wrote:
> 
> > Ingo Molnar wrote:
> >> * H. Peter Anvin <hpa@...or.com> wrote:
> >>
> >>>> I'm not sure how we could detect pure Qemu instances - perhaps it should 
> >>>> define some special MSR or something?
> >>> Perhaps they should fix the Qemu BIOS to actually simulate working MSRs; 
> >>> if nothing else, they should set up the default MTRR to be cachable.
> >>
> >> btw., should KVM do the same?
> >
> > Yes.  Especially since they share a BIOS.
> 
> ok. Then i guess we should just leave the warning and the backtrace in 
> place until they get a fix done?

No. I don't agree. The MTRRs are set up by the BIOS because it knows the
hardware best (I know this is only true in theory). The OS should
basically trust the BIOS MTRR settings. If the OS can't trust the BIOS,
like on real hardware, the check and the warning is necessary. If the OS
can trust the BIOS, like running in a KVM or QEMU virtual machine, it
should just ignore the case where all MTRRs are blank.

Joerg

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