KVM: s390: enable ibs only if available

Let's enable interlock-and-broadcast suppression only if the facility is
actually available.

Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/kvm/kvm-s390.c

@@ -2789,6 +2789,8 @@ static void __disable_ibs_on_all_vcpus(struct kvm *kvm)
 
 static void __enable_ibs_on_vcpu(struct kvm_vcpu *vcpu)
 {
+	if (!sclp.has_ibs)
+		return;
 	kvm_check_request(KVM_REQ_DISABLE_IBS, vcpu);
 	kvm_s390_sync_request(KVM_REQ_ENABLE_IBS, vcpu);
 }