On Wed, 25 Jul 2018 11:12:33 +0200
David Hildenbrand <da...@redhat.com> 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?
> - msa5-base
That's just the warning, but as things are continuing to work, it's
fine as well.
> - zpci
That one theoretically has a dependency on CONFIG_PCI, but as that is
always set, I think it's fine as well.
>
> This will result right now in the following warning when starting QEMU TCG
> with the "max" model:
> "qemu-system-s390x: warning: 'msa5-base' requires 'kimd-sha-512'."
>
> The "qemu" model (used as default in QEMU under TCG) will continue to
> work without such warnings. The "max" mdel in the current form
s/mdel/model/
> might be interesting for kvm-unit-tests (where we would e.g. now also
> test "msa5-base").
>
> The "max" model is neither static nor migration safe (like the "host"
> model). It is independent of the machine but dependends on the accelerator.
> It can be used to detect the maximum CPU model also under TCG from upper
> layers without having to care about CPU model names for CPU model
> expansion.
>
> Signed-off-by: David Hildenbrand <da...@redhat.com>
> ---
> target/s390x/cpu_models.c | 81 +++++++++++++++++++++++++++------------
> 1 file changed, 56 insertions(+), 25 deletions(-)
>
> +static void s390_max_cpu_model_initfn(Object *obj)
> +{
> + const S390CPUModel *max_model;
> + S390CPU *cpu = S390_CPU(obj);
> + Error *local_err = NULL;
> +
> + if (kvm_enabled() && !kvm_s390_cpu_models_supported()) {
> + /* "max" and "host" always work, even without CPU model support */
> + return;
> + }
> +
> + max_model = get_max_cpu_model(&local_err);
> + if (local_err) {
> + g_assert(kvm_enabled());
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)?
> + 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.
