Re: [PATCH 08/17] s390x/cpumodel: Fix UI to CPU features pcc-cmac-{aes,eaes}-256

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 29.04.20 10:54, Christian Borntraeger wrote:
> 
> 
> On 28.04.20 19:13, David Hildenbrand wrote:
>> On 28.04.20 18:34, Markus Armbruster wrote:
>>> Both s390_features[S390_FEAT_PCC_CMAC_AES_256].name and
>>> s390_features[S390_FEAT_PCC_CMAC_EAES_256].name is
>>> "pcc-cmac-eaes-256".  The former is obviously a pasto.
>>>
>>> Impact:
>>>
>>> * s390_feat_bitmap_to_ascii() misidentifies S390_FEAT_PCC_CMAC_AES_256
>>>   as "pcc-cmac-eaes-256".  Affects QMP commands query-cpu-definitions,
>>>   query-cpu-model-expansion, query-cpu-model-baseline,
>>>   query-cpu-model-comparison, and the error message when
>>>   s390_realize_cpu_model() fails in check_compatibility().
>>>
>>> * s390_realize_cpu_model() misidentifies it in check_consistency()
>>>   warnings.
>>>
>>> * s390_cpu_list() likewise.  Affects -cpu help.
>>>
>>> * s390_cpu_model_register_props() creates CPU property
>>>   "pcc-cmac-eaes-256" twice.  The second one fails, but the error is
>>>   ignored (a later commit will change that).  Results in a single
>>>   property "pcc-cmac-eaes-256" with the description for
>>>   S390_FEAT_PCC_CMAC_AES_256, and no property for
>>>   S390_FEAT_PCC_CMAC_EAES_256.  CPU properties are visible in CLI -cpu
>>>   and -device, QMP & HMP device_add, QMP device-list-properties, and
>>>   QOM introspection.
>>>
>>> Fix by deleting the wayward 'e'.
>>
>> Very nice catch - thanks!
>>
>> While this sounds very bad, it's luckily not that bad in practice
>> (currently).
>>
>> The feature (or rather, both features) is part of the feature group
>> "msa4". As long as we have all sub-features part of that group (which is
>> usually the case), we will always indicate "msa4" to the user, instead
>> of all the separate sub-features. So, expansion, baseline, comparison
>> will usually only work with "msa4".
>>
>> (in addition, current KVM is not capable of actually masking off these
>> sub-features, so it will still, always see the feature, even if not
>> explicitly specified via "-cpu X,pcc-cmac-aes-256=on)
>>
>> I think we should do stable backports.
> 
> makes sense, but I would like to do some testing upfront (old QEMU <-> new QEMU

So migration does work between a qemu with and without the patch for host-model and
custom model=z14.