[PATCH v1] qemu: monitor: substitute missing model name for host-passthrough
jdenemar at redhat.com
Wed Sep 23 13:50:01 UTC 2020
Collin, I apologize for not getting to you earlier.
On Wed, Sep 16, 2020 at 12:11:08 -0400, Collin Walling wrote:
> On 9/16/20 3:03 AM, Michal Privoznik wrote:
> > On 9/15/20 10:25 PM, Collin Walling wrote:
> >> One more ping in attempt to get this in the right direction. Otherwise
> >> I'll post my next idea and we can go from there :)
> > I agree with Peter that while the idea might look correct it's too deep.
> >> Thinking about this issue, should a host-passthough CPU definition be
> >> permitted for the baseline & comparison commands? The model represented
> >> under this mode is not considered migration safe and it may make sense
> >> to simply fail early since these commands aim to construct/determine a
> >> migratable CPU model, respectively.
> > Honestly, I don't know much about this CPU models area, but is that true
> > even for two identical hosts? Say I have two desktops next to each
> > other, with the same CPU and I want to migrate. I could use host model,
> > couldn't I?
> "Host-model" is an alias for a CPU model that closely represents the
> capabilities of the host machine (on s390, because this model is defined
> by the hypervisor, it can also be called the "hypervisor CPU model" --
> not an important detail).
> However, a guest running with the host-passthrough mode is not
> considered migration safe as that guest may covertly run with
> features/capabilities that are not directly exposed to the hypervisor.
Right, but migration may still be possible and working fine if both host
> From what I understand regarding the hypervisor-cpu-compare and
> hypervisor-cpu-baseline commands is that they aim to assist with
> determining the migratability of guests based on their CPU model and
> feature set (usually along with a host CPU in the equation as well).
Baseline with a host-passthrough CPU is not indeed very useful, but
compare could still be used and its usage is not limited to migration.
For example, you can use it to check whether a domain with a guest CPU
configuration can be started on a specific host before you actually try
to start it. And reporting host-passthrough as incompatible would be
Anyway, thanks for your patch, it was mostly correct, it just needed to
be done a bit higher in the call graph. Incidentally, Tim Wiederhake 
took this original patch and moved the change to the right place. The
authorship is still yours, so if you want to append you signed-off-by
tag there, I'll wait a bit before pushing Tim's patch.
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