[libvirt] Question about the host-model CPU mode

David Hildenbrand david at redhat.com
Fri Oct 20 13:16:07 UTC 2017

> Hi all,
> we recently encountered the problem that the 'host-model' [1] has to be
> related to the machine type of a domain. We have following problem:
>    Let's assume we've a z13 system with a QEMU 2.9 and we define a
>    domain using the default s390-virtio-ccw machine together with the
>    host-model CPU mode [1]. The definition will have the machine
>    expanded to s390-virtio-ccw-2.9 but retain the host-model CPU mode
>    in the domain definition. In a next step we upgrade to QEMU 2.10
>    (first version to recognize z14). Everything is still fine, even
>    though the machine runs in 2.9 compatibility mode. Finally we
>    upgrade to a z14. As a consequence it is not possible to start the
>    domain anymore as the machine type doesn't support our CPU host
>    model (which is expanded at start time of the domain).

Actually, what is the cause of that problem? I assume it is the gs
feature (gs_allowed)?

We should really avoid such things (..._allowed) for CPU model features
in the future and clue all new such stuff to cpumodel_allowed.




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