Re: [Qemu-devel] [PATCH v1 RFC 6/6] KVM: s390: add cpu model support

[Christian Borntraeger]

On 22/05/14 10:53, Paolo Bonzini wrote:
> Il 22/05/2014 10:23, Michael Mueller ha scritto:
>> On Wed, 21 May 2014 15:22:35 +0200
>> Alexander Graf <address@hidden> wrote:
>>
>> I have seen the slides from Eduardo which he presented during this years
>> DevConf in Brno and made my comments according the s390x implementation
>> on that. Is you will see, this is mostly overlapping except for the model
>> definition authority that I clearly see on qemu's side.
>>
>> See pdf attachment.
> 
> More comments:
> 
> - "Only one machine type in s390 case which is -machine s390-virtio-ccw"
> 
> This probably should change sooner or later, as soon as the implementation 
> becomes stable enough.  Versioning is necessary for live migration across 
> different QEMU version.  Perhaps start versioning in 2.2, i.e. start making 
> s390-virtio-ccw-2.1 an alias for s390-virtio-ccw now?
> 
> Note that new virtio device features can appear at any time outside the s390 
> code, and will take part in versioning as well.
> 
> - "No enforce option"
> 
> Strongly suggest making enforce the only possible behavior.
> 
> - "Not in the s390x case, because the KVM facility mask limits the cpu model 
> specific facilities"
> 
> What if the KVM facility mask changes?  For x86, nowadays new CPUID bits are 
> only introduced in KVM when a new processors comes out.  But if we introduced 
> an older CPUID bit, it would be a huge complication for backwards 
> compatibility.  Is it different for s390?
> 
> Paolo
> 

I guess we need to have a full picture here. Would this topic be suitable for 
the KVM call?

Christian