diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index abe60268335d..02f4c21c57f6 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -392,6 +392,7 @@ struct kvm_vcpu_stat {
 	u64 diagnose_10;
 	u64 diagnose_44;
 	u64 diagnose_9c;
+	u64 diagnose_9c_ignored;
 	u64 diagnose_258;
 	u64 diagnose_308;
 	u64 diagnose_500;
diff --git a/arch/s390/kvm/diag.c b/arch/s390/kvm/diag.c
index 45634b3d2e0a..3fb54ec2cf3e 100644
--- a/arch/s390/kvm/diag.c
+++ b/arch/s390/kvm/diag.c
@@ -158,14 +158,28 @@ static int __diag_time_slice_end_directed(struct kvm_vcpu *vcpu)
 
 	tid = vcpu->run->s.regs.gprs[(vcpu->arch.sie_block->ipa & 0xf0) >> 4];
 	vcpu->stat.diagnose_9c++;
-	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d", tid);
 
+	/* yield to self */
 	if (tid == vcpu->vcpu_id)
-		return 0;
+		goto no_yield;
 
+	/* yield to invalid */
 	tcpu = kvm_get_vcpu_by_id(vcpu->kvm, tid);
-	if (tcpu)
-		kvm_vcpu_yield_to(tcpu);
+	if (!tcpu)
+		goto no_yield;
+
+	/* target already running */
+	if (READ_ONCE(tcpu->cpu) >= 0)
+		goto no_yield;
+
+	if (kvm_vcpu_yield_to(tcpu) <= 0)
+		goto no_yield;
+
+	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: done", tid);
+	return 0;
+no_yield:
+	VCPU_EVENT(vcpu, 5, "diag time slice end directed to %d: ignored", tid);
+	vcpu->stat.diagnose_9c_ignored++;
 	return 0;
 }
 
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index d1ccc168c071..165dea4c7f19 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1477,8 +1477,7 @@ static int __inject_sigp_stop(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
 	return 0;
 }
 
-static int __inject_sigp_restart(struct kvm_vcpu *vcpu,
-				 struct kvm_s390_irq *irq)
+static int __inject_sigp_restart(struct kvm_vcpu *vcpu)
 {
 	struct kvm_s390_local_interrupt *li = &vcpu->arch.local_int;
 
@@ -2007,7 +2006,7 @@ static int do_inject_vcpu(struct kvm_vcpu *vcpu, struct kvm_s390_irq *irq)
 		rc = __inject_sigp_stop(vcpu, irq);
 		break;
 	case KVM_S390_RESTART:
-		rc = __inject_sigp_restart(vcpu, irq);
+		rc = __inject_sigp_restart(vcpu);
 		break;
 	case KVM_S390_INT_CLOCK_COMP:
 		rc = __inject_ckc(vcpu);
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index d047e846e1b9..d9e6bf3d54f0 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -155,6 +155,7 @@ struct kvm_stats_debugfs_item debugfs_entries[] = {
 	{ "instruction_diag_10", VCPU_STAT(diagnose_10) },
 	{ "instruction_diag_44", VCPU_STAT(diagnose_44) },
 	{ "instruction_diag_9c", VCPU_STAT(diagnose_9c) },
+	{ "diag_9c_ignored", VCPU_STAT(diagnose_9c_ignored) },
 	{ "instruction_diag_258", VCPU_STAT(diagnose_258) },
 	{ "instruction_diag_308", VCPU_STAT(diagnose_308) },
 	{ "instruction_diag_500", VCPU_STAT(diagnose_500) },
@@ -453,16 +454,14 @@ static void kvm_s390_cpu_feat_init(void)
 
 int kvm_arch_init(void *opaque)
 {
-	int rc;
+	int rc = -ENOMEM;
 
 	kvm_s390_dbf = debug_register("kvm-trace", 32, 1, 7 * sizeof(long));
 	if (!kvm_s390_dbf)
 		return -ENOMEM;
 
-	if (debug_register_view(kvm_s390_dbf, &debug_sprintf_view)) {
-		rc = -ENOMEM;
-		goto out_debug_unreg;
-	}
+	if (debug_register_view(kvm_s390_dbf, &debug_sprintf_view))
+		goto out;
 
 	kvm_s390_cpu_feat_init();
 
@@ -470,19 +469,17 @@ int kvm_arch_init(void *opaque)
 	rc = kvm_register_device_ops(&kvm_flic_ops, KVM_DEV_TYPE_FLIC);
 	if (rc) {
 		pr_err("A FLIC registration call failed with rc=%d\n", rc);
-		goto out_debug_unreg;
+		goto out;
 	}
 
 	rc = kvm_s390_gib_init(GAL_ISC);
 	if (rc)
-		goto out_gib_destroy;
+		goto out;
 
 	return 0;
 
-out_gib_destroy:
-	kvm_s390_gib_destroy();
-out_debug_unreg:
-	debug_unregister(kvm_s390_dbf);
+out:
+	kvm_arch_exit();
 	return rc;
 }
 
diff --git a/tools/testing/selftests/kvm/s390x/sync_regs_test.c b/tools/testing/selftests/kvm/s390x/sync_regs_test.c
index d5290b4ad636..b705637ca14b 100644
--- a/tools/testing/selftests/kvm/s390x/sync_regs_test.c
+++ b/tools/testing/selftests/kvm/s390x/sync_regs_test.c
@@ -25,12 +25,15 @@
 
 static void guest_code(void)
 {
-	register u64 stage asm("11") = 0;
-
-	for (;;) {
-		GUEST_SYNC(0);
-		asm volatile ("ahi %0,1" : : "r"(stage));
-	}
+	/*
+	 * We embed diag 501 here instead of doing a ucall to avoid that
+	 * the compiler has messed with r11 at the time of the ucall.
+	 */
+	asm volatile (
+		"0:	diag 0,0,0x501\n"
+		"	ahi 11,1\n"
+		"	j 0b\n"
+	);
 }
 
 #define REG_COMPARE(reg) \