[libvirt] inconsistent handling of "qemu64" CPU model

[Chris Friesen]

On 05/26/2016 04:41 AM, Jiri Denemark wrote:

> The qemu64 CPU model contains svm and thus libvirt will always consider
> it incompatible with any Intel CPUs (which have vmx instead of svm). On
> the other hand, QEMU by default ignores features that are missing in the
> host CPU and has no problem using qemu64 CPU, the guest just won't see
> some of the features defined in qemu64 model.
>
> In your case, you should be able to use
>
>      <cpu mode'custom' match='exact'>
>          <model>qemu64</model>
>          <feature name='svm' policy='disable'/>
>      </cpu>
>
> to get the same CPU model you'd get by default (if not, you may need to
> also add <feature name='vmx' policy='require'/>).
>
> Alternatively
>
>      <cpu mode'custom' match='exact'>
>          <model>qemu64</model>
>          <feature name='svm' policy='force'/>
>      </cpu>
>
> should work too (and it would be better in case you use it on an AMD
> host).

It's actually OpenStack that is setting up the XML, not me, so I'd have to 
special-case the "qemu64" model and it'd get ugly. :)

The question remains, why is "qemu64" okay when used implicitly but not 
explicitly?  I would have expected them to behave the same.


> But why you even want to use qemu64 CPU in a domain XML explicitly? If
> you're fine with that CPU, just let QEMU use a default one. If not, use
> a CPU model that fits your host/needs better.

Working around another issue would be simpler/cleaner if I could just explicitly 
set the model to qemu64.

Chris