[libvirt] Question about the host-model CPU mode

Marc Hartmayer mhartmay at linux.vnet.ibm.com
Thu Oct 5 08:46:24 UTC 2017

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. The definition will have the machine expanded to
s390-virtio-ccw-2.9 but retain the host-model CPU mode. 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).

Is this behavior expected?

There are some ways to avoid this problem:
- CPU model expansion is performed at domain definition time
- host-model is related to the machine type of a domain

Thank you in advance.

Beste Grüße / Kind regards
   Marc Hartmayer

IBM Deutschland Research & Development GmbH
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