Re: [PATCH v3 1/2] target/s390x: report deprecated-props in cpu-model-expansion reply

[Collin Walling <walling@linux.ibm.com>]

On 4/26/24 13:45, David Hildenbrand wrote:
> On 26.04.24 19:44, David Hildenbrand wrote:
>> On 24.04.24 23:56, Collin Walling wrote:
>>> Retain a list of deprecated features disjoint from any particular
>>> CPU model. A query-cpu-model-expansion reply will now provide a list of
>>> properties (i.e. features) that are flagged as deprecated. Example:
>>>
>>>       {
>>>         "return": {
>>>           "model": {
>>>             "name": "z14.2-base",
>>>             "deprecated-props": [
>>>               "bpb",
>>>               "csske"
>>>             ],
>>>             "props": {
>>>               "pfmfi": false,
>>>               "exrl": true,
>>>               ...a lot more props...
>>>               "skey": false,
>>>               "vxpdeh2": false
>>>             }
>>>           }
>>>         }
>>>       }
>>>
>>> It is recommended that s390 guests operate with these features
>>> explicitly disabled to ensure compatability with future hardware.
>>
>> Likely you should only report features that are applicable to a model.
>> that is, if it's part of the full_feat.
>>
>> Otherwise, the caller might simply want do set all features to "false",
>> and we'd fail setting a feature that is unknown to a specific CPU
>> generation.
>>
>> That is, you would AND the bitmap with the full_feat of the underlying
>> CPU definition.
> 
> Refreshing my memory, I think we can just clear any CPU features. We 
> only bail out when setting them!
> 

Very good point.  I've been working only with newer-gen machines and
would not have thought to test / catch that case.  I will filter the
deprecated-props array with features that are only available on the
full_model of the expanded CPU model.

-- 
Regards,
  Collin