[PATCH v4 0/2] query-cpu-model-expansion: report deprecated features

[Collin Walling]

Changelog

    v4
        - updated cover letter to show example output
        - deprecated features are now a subset of the full CPU model's
            list of features
            - value: 
                1. no longer listing the deprecated features for CPU
                     models that never had these features available in the
                     first place
                2. deprecated features will not show up for future CPU 
                     models that out-right drop these features
        - updated qapi documentation
            - now reflects that these props are a subset of the full
                model's definition of properties
            - added Since: tag to deprecated-props (assuming 9.1)

    v3
        - removed optional disable-deprecated-feats argument
        - added deprecated-props array to CpuModelInfo struct
        - amended cover letter language to reflect design

    v2 
        - removed "static-recommended" expansion type
        - implemented optional disable-deprecated-feats argument

---

The current implementation of query-cpu-model-expansion is lacking a way to 
retrieve
CPU models with properties (i.e. features) that are flagged as deprecated.  To 
remedy
this, a list of deprecated-props has been appended to the CpuModelInfo struct, 
and
will currently be reported by a query-cpu-model-expansion.  The features 
reported in
the output are a subset of the full CPU model expansion.

Output example with host-model (z14):

{
  "execute": "query-cpu-model-expansion",
  "arguments": {
    "type": "static",
    "model": {
      "name": "host"
    }
  }
}
{
  "return": {
    "model": {
      "name": "z14.2-base",
      "deprecated-props": [
        "bpb",
        "te",
        "cte",
        "csske"
      ],
      "props": {
        "aen": true,
        "cmmnt": true,
        "aefsi": true,
        "diag318": true,
        "mepoch": true,
        "msa8": true,
        "msa7": true,
        "msa6": true,
        "msa5": true,
        "msa4": true,
        "msa3": true,
        "msa2": true,
        "msa1": true,
        "sthyi": true,
        "edat": true,
        "ri": true,
        "edat2": true,
        "etoken": true,
        "vx": true,
        "ipter": true,
        "mepochptff": true,
        "ap": true,
        "vxeh": true,
        "vxpd": true,
        "esop": true,
        "apqi": true,
        "apft": true,
        "els": true,
        "iep": true,
        "apqci": true,
        "cte": true,
        "ais": true,
        "bpb": true,
        "ctop": true,
        "gs": true,
        "ppa15": true,
        "zpci": true,
        "sea_esop2": true,
        "te": true,
        "cmm": true
      }
    }
  }
}

Example output with an older CPU model:

{
  "execute": "query-cpu-model-expansion",
  "arguments": {
    "type": "static",
    "model": {
      "name": "z10EC"
    }
  }
}
{
  "return": {
    "model": {
      "name": "z10EC-base",
      "deprecated-props": [
        "bpb",
        "csske"
      ],
      "props": {
        "msa2": true,
        "msa1": true,
        "sthyi": true,
        "edat": true,
        "cmm": true
      }
    }
  }
}

A simple interface is designed that contains an array of feature bits that are 
flagged
as deprecated.  This list may be easily populated with more features in the 
future.

    void s390_get_deprecated_features(S390FeatBitmap features)
    {
        static const int feats[] = {
             /* CSSKE is deprecated on newer generations */
             S390_FEAT_CONDITIONAL_SSKE,
             S390_FEAT_BPB,
             /* Deprecated on z16 */
             S390_FEAT_CONSTRAINT_TRANSACTIONAL_EXE,
             S390_FEAT_TRANSACTIONAL_EXE
        };
        int i;

        for (i = 0; i < ARRAY_SIZE(feats); i++) {
            set_bit(feats[i], features);
        }
    }

Use case example:

Newer s390 machines may signal the end-of-support for particular CPU features,
rendering guests operating with older CPU models incapable of running on
said machines.  A manual effort to disable certain CPU features would be
required.

Reporting a list of deprecated features allows the user / management app to
take the next steps to ensure the guest is defined in a way that ensures
a migration in the future.

Collin L. Walling (2):
  target/s390x: report deprecated-props in cpu-model-expansion reply
  target/s390x: flag te and cte as deprecated

 qapi/machine-target.json         |  7 ++++++-
 target/s390x/cpu_features.c      | 17 +++++++++++++++++
 target/s390x/cpu_features.h      |  1 +
 target/s390x/cpu_models_sysemu.c |  8 ++++++++
 4 files changed, 32 insertions(+), 1 deletion(-)

-- 
2.43.0