KVM: s390: SIGP START has to report BUSY while stopping a CPU

Just like the RESTART order, the START order also has to report BUSY
while a STOP request is pending, to avoid that the START might be
ignored due to a race condition between the STOP and the START order.
Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>

arch/s390/include/asm/sigp.h

@@ -5,6 +5,7 @@
 #define SIGP_SENSE		      1
 #define SIGP_EXTERNAL_CALL	      2
 #define SIGP_EMERGENCY_SIGNAL	      3
+#define SIGP_START		      4
 #define SIGP_STOP		      5
 #define SIGP_RESTART		      6
 #define SIGP_STOP_AND_STORE_STATUS    9

arch/s390/kvm/sigp.c

@@ -455,6 +455,11 @@ int kvm_s390_handle_sigp(struct kvm_vcpu *vcpu)
 		rc = __sigp_sense_running(vcpu, cpu_addr,
 					  &vcpu->run->s.regs.gprs[r1]);
 		break;
+	case SIGP_START:
+		rc = sigp_check_callable(vcpu, cpu_addr);
+		if (rc == SIGP_CC_ORDER_CODE_ACCEPTED)
+			rc = -EOPNOTSUPP;    /* Handle START in user space */
+		break;
 	case SIGP_RESTART:
 		vcpu->stat.instruction_sigp_restart++;
 		rc = sigp_check_callable(vcpu, cpu_addr);