[libvirt] [PATCH 0/4] qemu: Use host-model CPU on s390 by default

[Jiri Denemark]

On Fri, Nov 15, 2019 at 15:55:04 +0100, Christian Borntraeger wrote:
> 
> 
> On 15.11.19 15:47, Jiri Denemark wrote:
> > On Fri, Nov 15, 2019 at 15:12:18 +0100, Boris Fiuczynski wrote:
> >> Just a heads up.
> >> After installing libvirt rpms of this branch all my existing kvm s390 
> >> domains ended up with
> >>
> >>    <cpu mode='custom' match='exact' check='none'>
> >>      <model fallback='forbid'>qemu</model>
> >>    </cpu>
> >>
> >> Newly defined domains without specified cpu do so as well.
> > 
> > Unless the domains are all TCG, it seems your QEMU is too old. You need
> > a fairly recent one which contains commit v4.1.0-1683-gde60a92ea7
> > (s390x/kvm: Set default cpu model for all machine classes)
> > 
> > I the domains all use KVM and you have new enough QEMU, there might be a
> > bug somewhere. Which should not happen :=)
> 
> So shouldnt libvirt fence this rework (add default model) to qemu 4.2 and newer?

Libvirt does all this only if query-machines returns default-cpu-type,
which is introduced in 4.2. But since it was introduced earlier, anyone
using qemu from git between the two commits will see this behavior.
Somewhat similar thing will happen on ppc64, but even with the current
master. Everything should be OK once QEMU 4.2.0 final release is used,
though (since it will contain all required patches).

Jirka