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Re: [Qemu-devel] [PATCH v1] s390x/cpu_models: Add "-cpu max" support
From: |
Cornelia Huck |
Subject: |
Re: [Qemu-devel] [PATCH v1] s390x/cpu_models: Add "-cpu max" support |
Date: |
Wed, 25 Jul 2018 14:06:31 +0200 |
On Wed, 25 Jul 2018 13:58:16 +0200
David Hildenbrand <address@hidden> wrote:
> On 25.07.2018 13:36, Cornelia Huck wrote:
> > On Wed, 25 Jul 2018 11:12:33 +0200
> > David Hildenbrand <address@hidden> wrote:
> >
> >> The "max" CPU model behaves like "-cpu host" when KVM is enabled, and like
> >> a CPU with the maximum possible feature set when TCG is enabled.
> >>
> >> While the "host" model can not be used under TCG ("kvm_required"), the
> >> "max" model can and "Enables all features supported by the accelerator in
> >> the current host".
> >>
> >> So we can treat "host" just as a special case of "max" (like x86 does).
> >> It differs to the "qemu" CPU model under TCG such that compatibility
> >> handling will not be performed and that some experimental CPU features
> >> not yet part of the "qemu" model might be indicated.
> >>
> >> These are right now under TCG (see "qemu_MAX"):
> >> - stfle53
> >
> > That's a z13 feature, so I think it's fine as we don't care about
> > machine generations for the max mode anyway, correct?
>
> Yes the max model really just is "give me anything you got and that you
> can expand to a static model (i.e. fully specify on the command line)".
>
> >
> >> - msa5-base
> >
> > That's just the warning, but as things are continuing to work, it's
> > fine as well.
>
> Yes, as these are z13 models we don't but them yet into our "stable"
> qemu model which is based on a z12.
>
> >
> >> - zpci
> >
> > That one theoretically has a dependency on CONFIG_PCI, but as that is
> > always set, I think it's fine as well.
>
> That is even already handled correctly, see
> target/s390x/cpu_models.c:register_types()
>
> 1314 #ifndef CONFIG_USER_ONLY
> 1315 if (!pci_available) {
> 1316 clear_bit(S390_FEAT_ZPCI, qemu_max_cpu_feat);
> 1317 }
> 1318 #endif
Oh, I actually added that myself :)
>
> [...]
>
> > Maybe add a comment that for kvm we try the host model, and only that
> > can fail (i.e., for tcg this will always work)?
>
> "we expect only errors under KVM, when we actually query the kernel"
"We expect errors only under KVM, where we actually query the kernel"
?
If nobody else has further comments, I can squash in the change and
queue it for 3.1. I'll let it sit for a bit longer on the list, though.
>
> >
> >> + error_report_err(local_err);
> >> + /* fallback to unsupported CPU models */
> >> + return;
> >> + }
> >> +
> >> + cpu->model = g_new(S390CPUModel, 1);
> >> + /* copy the CPU model so we can modify it */
> >> + memcpy(cpu->model, max_model, sizeof(*cpu->model));
> >> +}
> >> +
> >> static void s390_cpu_model_finalize(Object *obj)
> >> {
> >> S390CPU *cpu = S390_CPU(obj);
> >
> > Looks sane to me.
> >
>
> Thanks!
>
Re: [Qemu-devel] [PATCH v1] s390x/cpu_models: Add "-cpu max" support, Eduardo Habkost, 2018/07/25
Re: [Qemu-devel] [PATCH v1] s390x/cpu_models: Add "-cpu max" support, Cornelia Huck, 2018/07/27