KVM: s390: make sigp restart return busy when stop pending

On reboot the guest sends in smp_send_stop() a sigp stop to all CPUs
except for current CPU.  Then the guest switches to the IPL cpu by
sending a restart to the IPL CPU, followed by a sigp stop to the
current cpu. Since restart is handled by userspace it's possible that
the restart is delivered before the old stop.  This means that the IPL
CPU isn't restarted and we have no running CPUs. So let's make sure
that there is no stop action pending when we do the restart.

Signed-off-by: Jens Freimann <jfrei@linux.vnet.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

arch/s390/kvm/sigp.c

@@ -309,6 +309,34 @@ static int __sigp_sense_running(struct kvm_vcpu *vcpu, u16 cpu_addr,
 	return rc;
 }
 
+static int __sigp_restart(struct kvm_vcpu *vcpu, u16 cpu_addr)
+{
+	int rc = 0;
+	struct kvm_s390_float_interrupt *fi = &vcpu->kvm->arch.float_int;
+	struct kvm_s390_local_interrupt *li;
+
+	if (cpu_addr >= KVM_MAX_VCPUS)
+		return 3; /* not operational */
+
+	spin_lock(&fi->lock);
+	li = fi->local_int[cpu_addr];
+	if (li == NULL) {
+		rc = 3; /* not operational */
+		goto out;
+	}
+
+	spin_lock_bh(&li->lock);
+	if (li->action_bits & ACTION_STOP_ON_STOP)
+		rc = 2; /* busy */
+	else
+		VCPU_EVENT(vcpu, 4, "sigp restart %x to handle userspace",
+			cpu_addr);
+	spin_unlock_bh(&li->lock);
+out:
+	spin_unlock(&fi->lock);
+	return rc;
+}
+
 int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu)
 {
 	int r1 = (vcpu->arch.sie_block->ipa & 0x00f0) >> 4;
@@ -372,6 +400,9 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu)
 		break;
 	case SIGP_RESTART:
 		vcpu->stat.instruction_sigp_restart++;
+		rc = __sigp_restart(vcpu, cpu_addr);
+		if (rc == 2) /* busy */
+			break;
 		/* user space must know about restart */
 	default:
 		return -EOPNOTSUPP;