Re: [Qemu-devel] [qemu-s390x] [PATCH v1] s390x/cpu_models: Add "-cpu max" support

[David Hildenbrand <david@redhat.com>]

On 27.07.2018 14:55, Cornelia Huck wrote:
> On Wed, 25 Jul 2018 11:12:33 +0200
> David Hildenbrand <david@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
>> - msa5-base
>> - zpci
>>
>> 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
>> 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 <david@redhat.com>
>> ---
>>  target/s390x/cpu_models.c | 81 +++++++++++++++++++++++++++------------
>>  1 file changed, 56 insertions(+), 25 deletions(-)
> 
> So, what's the outcome? Can I merge this with the discussed minor
> edits, or should I wait for a v2?
> 

Eduardo identified possible optimizations independent of this patch, so
we should be good to go. @Eduardo, please correct me if I'm wrong!

-- 

Thanks,

David / dhildenb