KVM: s390: activate GISA for emulated interrupts

If the AIV facility is available, a GISA will be used to manage emulated
adapter interrupts.

Signed-off-by: Michael Mueller <mimu@linux.vnet.ibm.com>
Reviewed-by: Halil Pasic <pasic@linux.vnet.ibm.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Cornelia Huck <cohuck@redhat.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/kvm/interrupt.c

@@ -2842,7 +2842,13 @@ void kvm_s390_gisa_clear(struct kvm *kvm)
 
 void kvm_s390_gisa_init(struct kvm *kvm)
 {
-	/* not implemented yet */
+	if (!css_general_characteristics.aiv)
+		kvm->arch.gisa = NULL;
+	else {
+		kvm->arch.gisa = &kvm->arch.sie_page2->gisa;
+		VM_EVENT(kvm, 3, "gisa 0x%pK initialized", kvm->arch.gisa);
+		kvm_s390_gisa_clear(kvm);
+	}
 }
 
 void kvm_s390_gisa_destroy(struct kvm *kvm)