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

[Cornelia Huck <cohuck@redhat.com>]

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?