From mboxrd@z Thu Jan  1 00:00:00 1970
From: Cornelia Huck <cohuck@redhat.com>
Subject: Re: [PATCH v2 12/12] KVM: s390: introduce the format-1 GISA
Date: Thu, 25 Jan 2018 16:47:51 +0100
Message-ID: <20180125164751.3034a45d.cohuck@redhat.com>
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        <e1e0ef1e-1311-af08-faff-72b116ce4a9d@redhat.com>
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Cc: David Hildenbrand <david@redhat.com>, KVM <kvm@vger.kernel.org>,
        linux-s390 <linux-s390@vger.kernel.org>,
        Janosch Frank <frankja@linux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>,
        Michael Mueller <mimu@linux.vnet.ibm.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>
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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?