On 10/20/2017 03:43 PM, David Hildenbrand wrote:
> On 20.10.2017 15:36, Christian Borntraeger wrote:
>>
>>
>> On 10/20/2017 03:16 PM, David Hildenbrand wrote:
>>>
>>>> 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.
>>
>> Yes, starting a guest with
>> <os>
>> <type arch='s390x' machine='s390-ccw-virtio-2.9'>hvm</type>
>> </os>
>> <cpu mode='host-model'/>
>>
>> results in
>>
>> qemu-system-s390x: Some features requested in the CPU model are not available in the configuration: gs
>>
>> Tying it to cpumodel_allowed would not help, migration-wise though.
>> libvirt would still transform
>>
>> <os>
>> <type arch='s390x' machine='s390-ccw-virtio-2.9'>hvm</type>
>> </os>
>> <cpu mode='host-model'/>
>
> My point was, that the host model would have to be copied and _remain_
> there when s390-ccw-virtio was expanded to s390-ccw-virtio-2.9.
>
> So really replacing <cpu mode='host-model'/> by the model z13-base....
> This would at least fix this issue. Just like s390-ccw-virtio get's
> replaced and remains thats way.
>
> But this might for sure have other problems.
The problem goes much further.
A fresh guest with
<os>
<type arch='s390x' machine='s390-ccw-virtio-2.9'>hvm</type>
</os>
<cpu mode='host-model'/>
does not start. No migration from an older system is necessary.
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