Re: [qemu-s390x] [PATCH 10/10] s390x/cpumodel: do not claim csske for expanded models in qmp

[David Hildenbrand]

On 18.04.19 13:31, Christian Borntraeger wrote:
> While we have removed csske and bpb from the default model, the very
> common case of "host-model" in libvirt (expanded to a base model
> + features) would still contain bpb and csske. This can prevent
> migration to a future machine for a host-model machine. Let us fence
> bpb and csske when we run on a generation 15. If necessary the
> user can still use -cpu 8561,csske=on,bpb=on to force enable these
> features.
> 
> Signed-off-by: Christian Borntraeger <address@hidden>
> ---
>  target/s390x/cpu_models.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/target/s390x/cpu_models.c b/target/s390x/cpu_models.c
> index e727519686..03bdca1fb8 100644
> --- a/target/s390x/cpu_models.c
> +++ b/target/s390x/cpu_models.c
> @@ -629,6 +629,17 @@ CpuModelExpansionInfo 
> *qmp_query_cpu_model_expansion(CpuModelExpansionType type,
>          return NULL;
>      }
>  
> +    /*
> +     * Do not claim CSSKE and BPB if the host model expands to
> +     * generation 15 or newer
> +     */
> +    if (s390_model.def->gen >= 15) {
> +        clear_bit(S390_FEAT_CONDITIONAL_SSKE,
> +                  (unsigned long *) &s390_model.features);
> +        clear_bit(S390_FEAT_BPB,
> +                  (unsigned long *) &s390_model.features);
> +    }
> +
>      if (type == CPU_MODEL_EXPANSION_TYPE_STATIC) {
>          delta_changes = true;
>      } else if (type != CPU_MODEL_EXPANSION_TYPE_FULL) {
> 

The bad thing about it is, it hinders migration *to* this hw generation.
Will have to think about this some more. As alternative, simply ignore
S390_FEAT_CONDITIONAL_SSKE and S390_FEAT_BPB when baselining/comparing.

-- 

Thanks,

David / dhildenb