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

[john cooper]

Dor Laor wrote:
> On 12/22/2009 12:51 AM, john cooper wrote:
>> Dor Laor wrote:
>>
>>> Qemu will check the required cpuid of the cpu model on the host and
>>> refuse to load otherwise. When moving to this model, migration can be
>>> simplified too since there are fewer combination, and one can choose
>>> performance over migration flexibility and wise versa.
>>> Due to the above check, the destination qemu won't load if the host
>>> does not support its cpu model.
>>
>> If you're referring to the check in my patch, that's
>> currently advisory only.
>>
>> The existing cpu model encoding of CPUID tosses flags
>> in to the soup on speculation they may be available
>> on the host. If not it assumes they will be quietly
>> disabled on their way to the guest along with whatever
> 
> why not shout loudly and abort? Do you want windows to reactivate itself?

This was the existing behavior of that code which
expected certain requested flags to be casually
dropped.  But bailing after the warning is probably
fine as well given the warning itself is optional
and bailing wouldn't happen by default.

That code could probably use a cleanup going forward
to iron out such issues.  Andre mentioned he had
pending patches which in part addressed this so I
thought to let those resolve beforehand.

Thanks,

-john

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