Re: [Qemu-devel] [PATCH v3 30/30] target/s390x: update maximum TCG model to z800

[Aurelien Jarno]

On 2017-06-01 21:56, David Hildenbrand wrote:
> On 01.06.2017 21:17, Aurelien Jarno wrote:
> > On 2017-06-01 10:38, David Hildenbrand wrote:
> >> On 01.06.2017 00:01, Aurelien Jarno wrote:
> >>> At the same time fix the TCG version of get_max_cpu_model to return the
> >>> maximum model like on KVM. Remove the ETF2 and long-displacement
> >>
> >> I don't understand the part
> >> "fix the TCG version of get_max_cpu_model to return the maximum model
> >> like on KVM".
> >>
> >> Can you elaborate?
> > 
> > Currently get_max_cpu_model returns the features of the base model, so
> > for example the one of a z900 even on a z800. This makes impossible to
> > enable the features that are provided by a z800 like etf2 or ldisp.
> > 
> 
> Right, you can always change the max_cpu_model, e.g. bumping up the
> version or adding new features, that is just fine.
> 
> > For what I understand from the KVM code (but I haven't tested), the
> > function return all the features that are supported by the current CPU,
> > not all the features that are supported by the base model of the current
> > CPU.
> 
> Correct, for KVM it is the detected model, that means: Base features +
> optional features.
> 
> 
> > 
> > 
> >>> facilities from the additional features as it is included in the z800.
> >>>
> >>> Signed-off-by: Aurelien Jarno <address@hidden>
> >>> ---
> >>>  target/s390x/cpu_models.c | 13 ++++++-------
> >>>  1 file changed, 6 insertions(+), 7 deletions(-)
> >>>
> >>> diff --git a/target/s390x/cpu_models.c b/target/s390x/cpu_models.c
> >>> index fc3cb25cc3..c13bbd852c 100644
> >>> --- a/target/s390x/cpu_models.c
> >>> +++ b/target/s390x/cpu_models.c
> >>> @@ -668,8 +668,6 @@ static void 
> >>> add_qemu_cpu_model_features(S390FeatBitmap fbm)
> >>>      static const int feats[] = {
> >>>          S390_FEAT_STFLE,
> >>>          S390_FEAT_EXTENDED_IMMEDIATE,
> >>> -        S390_FEAT_EXTENDED_TRANSLATION_2,
> >>> -        S390_FEAT_LONG_DISPLACEMENT,
> >>>          S390_FEAT_LONG_DISPLACEMENT_FAST,
> >>>          S390_FEAT_ETF2_ENH,
> >>>          S390_FEAT_STORE_CLOCK_FAST,
> >>> @@ -696,9 +694,9 @@ static S390CPUModel *get_max_cpu_model(Error **errp)
> >>>      if (kvm_enabled()) {
> >>>          kvm_s390_get_host_cpu_model(&max_model, errp);
> >>>      } else {
> >>> -        /* TCG emulates a z900 (with some optional additional features) 
> >>> */
> >>> -        max_model.def = &s390_cpu_defs[0];
> >>> -        bitmap_copy(max_model.features, max_model.def->default_feat,
> >>> +        /* TCG emulates a z800 (with some optional additional features) 
> >>> */
> >>> +        max_model.def = s390_find_cpu_def(0x2066, 7, 3, NULL);
> >>> +        bitmap_copy(max_model.features, max_model.def->full_feat,
> >>>                      S390_FEAT_MAX);
> >>>          add_qemu_cpu_model_features(max_model.features);
> >>>      }
> >>> @@ -956,8 +954,9 @@ static void s390_qemu_cpu_model_initfn(Object *obj)
> >>>      S390CPU *cpu = S390_CPU(obj);
> >>>  
> >>>      cpu->model = g_malloc0(sizeof(*cpu->model));
> >>> -    /* TCG emulates a z900 (with some optional additional features) */
> >>> -    memcpy(&s390_qemu_cpu_defs, &s390_cpu_defs[0], 
> >>> sizeof(s390_qemu_cpu_defs));
> >>> +    /* TCG emulates a z800 (with some optional additional features) */
> >>> +    memcpy(&s390_qemu_cpu_defs, s390_find_cpu_def(0x2066, 7, 3, NULL),
> >>> +           sizeof(s390_qemu_cpu_defs));
> >>
> >> No changing the qemu model without compatibility handling.
> > 
> > This patch series is based on the patch from Thomas Huth. It means the
> > QEMU model is still based on a z900, but that it is possible to enable
> > some more features like etf2.
> 
> Thomas' code did neither change features nor the "model definition". It
> just allows for some more feature to be set. It is a hack.
> 
> I am pretty sure that expanding the "qemu" CPU model now (QMP
> query-cpu-model-expansion) will indicate a z800, not a z900.
> 
> See cpu_info_from_model(). And that is a problem, because the QEMU CPU
> model is a "migration-safe" CPU model, meaning it must remain equal for
> every compatibility machine.
> 

Ok, I get what you mean now.

Aurelien

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
address@hidden                 http://www.aurel32.net