Re: [PATCH v2 12/12] KVM: s390: introduce the format-1 GISA

[Cornelia Huck <cohuck@redhat.com>]

On Thu, 25 Jan 2018 17:51:24 +0100
Christian Borntraeger <borntraeger@de.ibm.com> wrote:

> On 01/25/2018 05:17 PM, Cornelia Huck wrote:
> > On Thu, 25 Jan 2018 17:12:59 +0100
> > Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >   
> >> On 01/25/2018 04:47 PM, Cornelia Huck wrote:  
> >>> On Thu, 25 Jan 2018 16:43:27 +0100
> >>> Christian Borntraeger <borntraeger@de.ibm.com> wrote:
> >>>     
> >>>> On 01/25/2018 04:31 PM, David Hildenbrand wrote:
> >>>> [...]    
> >>>>>>  struct kvm_s390_vsie {
> >>>>>> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> >>>>>> index 68d7eef..efde264 100644
> >>>>>> --- a/arch/s390/kvm/kvm-s390.c
> >>>>>> +++ b/arch/s390/kvm/kvm-s390.c
> >>>>>> @@ -2518,6 +2518,8 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm,
> >>>>>>  	vcpu->arch.sie_block->icpua = id;
> >>>>>>  	spin_lock_init(&vcpu->arch.local_int.lock);
> >>>>>>  	vcpu->arch.sie_block->gd = (u32)(u64)kvm->arch.gisa;
> >>>>>> +	if (vcpu->arch.sie_block->gd && sclp.has_gisaf)
> >>>>>> +		vcpu->arch.sie_block->gd |= GISA_FORMAT1;
> >>>>>>  	seqcount_init(&vcpu->arch.cputm_seqcount);
> >>>>>>  
> >>>>>>  	rc = kvm_vcpu_init(vcpu, kvm, id);
> >>>>>>      
> >>>>>
> >>>>> So, what does this bring us? We don't seem to be using any new GISA-1
> >>>>> features.      
> >>>>
> >>>> Preparation for device pass-through interrupt forwarding.
> >>>>    
> >>>
> >>> Should we start out with a dual format-0/format-1 gisa block, then?
> >>> IIUC, you'll switch to gisa-1 if the facility is there and gisa-1 can
> >>> do anything that gisa-0 can do?    
> >>
> >> There might be systems that only have gisa-0, so I think having both makes
> >> sense.
> >>  
> > 
> > Yes, that's what I meant. Just do it earlier in the series - this patch
> > feels like an afterthought with no real user.  
> 
> I added 
> 
> A format-1 can do everything that format-0 can and we will need it
> for real HW passthrough. As there are systems with only format-0
> we keep both variants.
> 
> to the patch description. Maybe its now a bit less odd?

Also fine with me.

(I'll do a proper review round through the patches later.)