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

[Michael S. Tsirkin]

On Mon, Dec 14, 2009 at 02:18:33PM -0600, Anthony Liguori wrote:
> Michael S. Tsirkin wrote:
>> This might help 32 bit guests, but not guests with 64 bit
>> kernel and 32 bit userspace (my case) because all 64 bit
>> CPUs advertise syscall bit in cpuid. Thus 64 bit guests
>> do not seem to even bother checking this bit:
>> AMD + 64 bit -> syscall.
>>   
>
> Okay, I don't see a great option other than migrating the vendor_id string.

This won't help with kernels <2.6.32 though.  I guess we can switch
default vendor to Intel, this likely has some other side effects.

> Otherwise, cross vendor migration will not work by default.  Maybe  
> that's not a problem but if so, we really should change the default cpu  
> model to be much more aggressive about exposing host features.
> 
> Regards,
>
> Anthony Liguori

It's a tradeoff, but yes.  We also need more sanity checks and
management commands giving management tools to understand whether
emulating guest CPU X on host CPU Y is safe/possible, and which guests
this might break.

-- 
MST