[libvirt] [PATCH] qemu: caps: use model "qemu" for s390 tcg cpu-model-expansion

[David Hildenbrand]

On 24.07.2018 18:59, Daniel P. Berrangé wrote:
> On Tue, Jul 24, 2018 at 06:53:54PM +0200, Cornelia Huck wrote:
>> On Tue, 24 Jul 2018 18:08:21 +0200
>> Jiri Denemark <jdenemar at redhat.com> wrote:
>>
>>> On Mon, Jul 23, 2018 at 17:45:33 -0400, Collin Walling wrote:
>>>> Use model name "qemu" instead of "max" when calling
>>>> query-cpu-model-expansion for s390 on tcg.
>>>>
>>>> Signed-off-by: Collin Walling <walling at linux.ibm.com>
>>>> ---
>>>>  src/qemu/qemu_capabilities.c | 5 ++++-
>>>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
>>>> index 23b4833..e9b44cc 100644
>>>> --- a/src/qemu/qemu_capabilities.c
>>>> +++ b/src/qemu/qemu_capabilities.c
>>>> @@ -2356,7 +2356,10 @@ virQEMUCapsProbeQMPHostCPU(virQEMUCapsPtr qemuCaps,
>>>>  
>>>>      if (tcg || !virQEMUCapsGet(qemuCaps, QEMU_CAPS_KVM)) {
>>>>          virtType = VIR_DOMAIN_VIRT_QEMU;
>>>> -        model = "max";
>>>> +        if (ARCH_IS_S390(qemuCaps->arch))
>>>> +            model = "qemu";
>>>> +        else
>>>> +            model = "max";  
>>>
>>> I think we should also check if "max" is a supported model
>>> (qemuCaps->tcgCPUModels is already populated at this point) and only use
>>> "qemu" on s390 if "max" is not supported. And please, report the issue
>>> to QEMU developers since one of the reasons behind "max" is its
>>> universal availability on everywhere CPU model expansion is supported.
>>
>> Hm, can you point me to that discussion? A quick search through the
>> QEMU log gives me the addition of the "max" model on i386 as a
>> replacement to the "host" model for !kvm, but nothing about it being
>> universal...
> 
> I don't recall the link but "max" is supposed to be the standard shorthand
> for "enable all the features supported by the virt type". IOW, 'max' should
> work both KVM and TCG ("host" was only well defined for KVM), and across
> all architectures.

I remember the discussions and I agreed back than that this was the
right thing to do.

Looks like x86, arm and ppc have it. We should have it, too.

> 
> So having to use a different name on s390 is a bug in QEMU imho.
> 

While this should be fixed, it is compat handling and not really a BUG.

> Regards,
> Daniel
> 


-- 

Thanks,

David / dhildenb