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Date: Mon, 27 May 2013 14:21:36 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH] target-i386: Disable CPUID_EXT_MONITOR
	when KVM is enabled
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To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Igor Mammedov <imammedo@redhat.com>, Bandan Das <bsd@redhat.com>, qemu-devel@nongnu.org, =?ISO-8859-1?Q?Andreas_F=E4rber?= <afaerber@suse.de>

Il 27/05/2013 14:09, Eduardo Habkost ha scritto:
> On Sat, May 25, 2013 at 08:25:49AM +0200, Paolo Bonzini wrote:
>> Il 25/05/2013 03:21, Bandan Das ha scritto:
>>> There is one user-visible effect: "-cpu ...,enforce" will stop failing
>>> because of missing KVM support for CPUID_EXT_MONITOR. But that's exactly
>>> the point: there's no point in having CPU model definitions that would
>>> never work as-is with neither TCG or KVM. This patch is changing the
>>> meaning of (e.g.) "-machine ...,accel=kvm -cpu Opteron_G3" to match what
>>> was already happening in practice.
>>
>> But then -cpu Opteron_G3 does not match a "real" Opteron G3.  Is it
>> worth it?
> 
> No models match a "real" CPU this way, because neither TCG or KVM
> support all features supported by a real CPU. I ask the opposite
> question: is it worth maintaining an "accurate" CPU model definition
> that would never work without feature-bit tweaking in the command-line?

It would work with TCG.  Changing TCG to KVM should not change hardware
if you use "-cpu ...,enforce", so it is right that it fails when
starting with KVM.

Paolo