Re: [Qemu-devel] cpuid problem in upstream qemu with kvm

[Alexander Graf]

On 20.12.2009, at 18:18, Michael S. Tsirkin wrote:

> On Sun, Dec 20, 2009 at 06:17:02PM +0100, Alexander Graf wrote:
>> 
>> On 20.12.2009, at 17:56, Michael S. Tsirkin wrote:
>> 
>>> On Sun, Dec 20, 2009 at 05:59:33PM +0200, Avi Kivity wrote:
>>>> On 12/20/2009 05:51 PM, Michael S. Tsirkin wrote:
>>>>> 
>>>>>> Maybe we should make -cpu host the default.  That will give the best
>>>>>> performance for casual users, more testing for newer features, and will
>>>>>> force management apps to treat migration much more seriously.  The
>>>>>> downside is that casual users upgrading their machines might experience
>>>>>> issues with Windows.  Feature compatibility is not just about migration.
>>>>>> 
>>>>> This seems very aggressive.  Can't we whitelist features that we know
>>>>> about?  Further, doesn't KVM already do this?
>>>>> 
>>>>> 
>>>> 
>>>> It does, but without -cpuid host you're stuck with qemu64 (kvm.ko  
>>>> doesn't add features userspace didn't request).
>>> 
>>> Hmm, then, shouldn't either kvm or qemu mask features that we do not
>>> emulate well enough to make windows not crash?
>> 
>> -cpu host does that already, no?
>> 
>> Alex
> 
> I expected so, but Avi here seems to say windows will crash if you
> use a new CPU with it ...

Avi, have you narrowed it down to a specific feature bit?

Alex