[PATCH v1] qemu: monitor: substitute missing model name for host-passthrough

[Collin Walling]

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.

>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).

When the user passes an XML file to the hypervisor-cpu-compare and
hypervisor-cpu-baseline (sorry, forgot to be specific with the commands
here), AND the XML file contains a CPU definition using
mode='host-passthrough', then the commands should mention that this CPU
model is not migratable because the CPU definition using
host-passthrough is not migration safe.

>>
>> Perhaps if a host-passthrough CPU is detected, then an error reporting
>> something along the lines of "host-passthrough is not supported for
>> migration" would be sufficient for this?
>>
>> Thanks again. Hope all is well.
> 
> Michal
> 


-- 
Regards,
Collin

Stay safe and stay healthy