linux-kernel - Re: KVM warning about uncertified CPU for SMP for AMD model 2, stepping 3

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Message-ID: <4BB33C0D.9090808@amd.com>
Date:	Wed, 31 Mar 2010 14:11:57 +0200
From:	Andre Przywara <andre.przywara@....com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Jiri Kosina <jkosina@...e.cz>, Ingo Molnar <mingo@...e.hu>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	Joerg Roedel <joerg.roedel@....com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: KVM warning about uncertified CPU for SMP for AMD model 2, stepping
 3

Andi Kleen wrote:
> On Wed, Mar 31, 2010 at 01:03:02AM +0200, Jiri Kosina wrote:
>> Hi,
>>
>> booting 32bit guest on 32bit host on AMD system gives me the following 
>> warning when KVM is instructed to boot as SMP:
> 
> I guess these warnings could be just disabled. With nearly everyone
> using multi-core these days they are kind of obsolete anyways.
Well, the warning refers to an old single-core only CPU model. Most of 
those were able to run in SMP boards, but only a subset of them was 
officially certified to do so (Athlon-MP instead of Athlon-XP).
To avoid complaints about instability of such systems, the warning was 
introduced. If you consider these systems still supported, I wouldn't 
disable this warning, at least the check should be disabled only if the 
hypervisor CPUID bit is set.

But the far better solution is to instruct QEMU/KVM to inject a better 
CPU model (as it was suggested by some people two weeks ago). I am about 
to test various guests with respect to their behavior regarding 
different family/model/stepping settings (one issue is already fixed). 
If this goes well, I will send out the patch to inject the host's CPUID 
F/M/S into the guest by default (which has other advantages, but denies 
migration mostly).

BTW.: I encourage people to test their KVM guests with "-cpu host" (on 
newer QEMUs) and send me any crash logs.

Regards,
Andre.

-- 
Andre Przywara
AMD-Operating System Research Center (OSRC), Dresden, Germany
Tel: +49 351 448-3567-12

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