S390 needs a fast path for irq injection, and along those lines we 
introduce kvm_arch_set_irq_inatomic. Instead of placing all interrupts on
the global work queue as it does today, this patch provides a fast path for
irq injection.

The inatomic fast path cannot lose control since it is running with
interrupts disabled. This meant making the following changes that exist on 
the slow path today. First, the adapter_indicators page needs to be mapped
since it is accessed with interrupts disabled, so we added map/unmap
functions. Second, access to shared resources between the fast and slow 
paths needed to be changed from mutex and semaphores to spin_lock's.
Finally, the memory allocation on the slow path utilizes GFP_KERNEL_ACCOUNT
but we had to implement the fast path with GFP_ATOMIC allocation. Each of
these enhancements were required to prevent blocking on the fast inject
path.

Fencing of Fast Inject in Secure Execution environments is enabled in the
patch series by not mapping adapter indicator pages. In Secure Execution
environments the path of execution available before this patch is followed.

Statistical counters have been added to enable analysis of irq injection on
the fast path and slow path including io_390_inatomic, io_flic_inject_airq,
io_set_adapter_int and io_390_inatomic_adapter_masked.

Signed-off-by: Douglas Freimuth <freimuth@linux.ibm.com>
---
 arch/s390/include/asm/kvm_host.h |   6 +-
 arch/s390/kvm/interrupt.c        | 154 +++++++++++++++++++++++++++----
 arch/s390/kvm/kvm-s390.c         |  24 ++++-
 arch/s390/kvm/kvm-s390.h         |   3 +-
 4 files changed, 160 insertions(+), 27 deletions(-)

diff --git a/arch/s390/include/asm/kvm_host.h b/arch/s390/include/asm/kvm_host.h
index a078420751a1..90b1a19074ce 100644
--- a/arch/s390/include/asm/kvm_host.h
+++ b/arch/s390/include/asm/kvm_host.h
@@ -359,7 +359,7 @@ struct kvm_s390_float_interrupt {
 	struct kvm_s390_mchk_info mchk;
 	struct kvm_s390_ext_info srv_signal;
 	int last_sleep_cpu;
-	struct mutex ais_lock;
+	spinlock_t ais_lock;
 	u8 simm;
 	u8 nimm;
 };
@@ -450,6 +450,10 @@ struct kvm_vm_stat {
 	u64 inject_io;
 	u64 io_390_adapter_map;
 	u64 io_390_adapter_unmap;
+	u64 io_390_inatomic;
+	u64 io_flic_inject_airq;
+	u64 io_set_adapter_int;
+	u64 io_390_inatomic_adapter_masked;
 	u64 inject_float_mchk;
 	u64 inject_pfault_done;
 	u64 inject_service_signal;
diff --git a/arch/s390/kvm/interrupt.c b/arch/s390/kvm/interrupt.c
index 48d05a230416..d980b432b173 100644
--- a/arch/s390/kvm/interrupt.c
+++ b/arch/s390/kvm/interrupt.c
@@ -1963,15 +1963,10 @@ static int __inject_vm(struct kvm *kvm, struct kvm_s390_interrupt_info *inti)
 }
 
 int kvm_s390_inject_vm(struct kvm *kvm,
-		       struct kvm_s390_interrupt *s390int)
+		       struct kvm_s390_interrupt *s390int, struct kvm_s390_interrupt_info *inti)
 {
-	struct kvm_s390_interrupt_info *inti;
 	int rc;
 
-	inti = kzalloc_obj(*inti, GFP_KERNEL_ACCOUNT);
-	if (!inti)
-		return -ENOMEM;
-
 	inti->type = s390int->type;
 	switch (inti->type) {
 	case KVM_S390_INT_VIRTIO:
@@ -2284,6 +2279,7 @@ static int flic_ais_mode_get_all(struct kvm *kvm, struct kvm_device_attr *attr)
 {
 	struct kvm_s390_float_interrupt *fi = &kvm->arch.float_int;
 	struct kvm_s390_ais_all ais;
+	unsigned long flags;
 
 	if (attr->attr < sizeof(ais))
 		return -EINVAL;
@@ -2291,10 +2287,10 @@ static int flic_ais_mode_get_all(struct kvm *kvm, struct kvm_device_attr *attr)
 	if (!test_kvm_facility(kvm, 72))
 		return -EOPNOTSUPP;
 
-	mutex_lock(&fi->ais_lock);
+	spin_lock_irqsave(&fi->ais_lock, flags);
 	ais.simm = fi->simm;
 	ais.nimm = fi->nimm;
-	mutex_unlock(&fi->ais_lock);
+	spin_unlock_irqrestore(&fi->ais_lock, flags);
 
 	if (copy_to_user((void __user *)attr->addr, &ais, sizeof(ais)))
 		return -EFAULT;
@@ -2632,6 +2628,7 @@ static int modify_ais_mode(struct kvm *kvm, struct kvm_device_attr *attr)
 	struct kvm_s390_float_interrupt *fi = &kvm->arch.float_int;
 	struct kvm_s390_ais_req req;
 	int ret = 0;
+	unsigned long flags;
 
 	if (!test_kvm_facility(kvm, 72))
 		return -EOPNOTSUPP;
@@ -2648,7 +2645,7 @@ static int modify_ais_mode(struct kvm *kvm, struct kvm_device_attr *attr)
 				       2 : KVM_S390_AIS_MODE_SINGLE :
 				       KVM_S390_AIS_MODE_ALL, req.mode);
 
-	mutex_lock(&fi->ais_lock);
+	spin_lock_irqsave(&fi->ais_lock, flags);
 	switch (req.mode) {
 	case KVM_S390_AIS_MODE_ALL:
 		fi->simm &= ~AIS_MODE_MASK(req.isc);
@@ -2661,7 +2658,7 @@ static int modify_ais_mode(struct kvm *kvm, struct kvm_device_attr *attr)
 	default:
 		ret = -EINVAL;
 	}
-	mutex_unlock(&fi->ais_lock);
+	spin_unlock_irqrestore(&fi->ais_lock, flags);
 
 	return ret;
 }
@@ -2675,25 +2672,33 @@ static int kvm_s390_inject_airq(struct kvm *kvm,
 		.parm = 0,
 		.parm64 = isc_to_int_word(adapter->isc),
 	};
+	struct kvm_s390_interrupt_info *inti;
+	unsigned long flags;
+
 	int ret = 0;
 
+	inti = kzalloc_obj(*inti, GFP_KERNEL_ACCOUNT);
+	if (!inti)
+		return -ENOMEM;
+
 	if (!test_kvm_facility(kvm, 72) || !adapter->suppressible)
-		return kvm_s390_inject_vm(kvm, &s390int);
+		return kvm_s390_inject_vm(kvm, &s390int, inti);
 
-	mutex_lock(&fi->ais_lock);
+	spin_lock_irqsave(&fi->ais_lock, flags);
 	if (fi->nimm & AIS_MODE_MASK(adapter->isc)) {
 		trace_kvm_s390_airq_suppressed(adapter->id, adapter->isc);
+		kfree(inti);
 		goto out;
 	}
 
-	ret = kvm_s390_inject_vm(kvm, &s390int);
+	ret = kvm_s390_inject_vm(kvm, &s390int, inti);
 	if (!ret && (fi->simm & AIS_MODE_MASK(adapter->isc))) {
 		fi->nimm |= AIS_MODE_MASK(adapter->isc);
 		trace_kvm_s390_modify_ais_mode(adapter->isc,
 					       KVM_S390_AIS_MODE_SINGLE, 2);
 	}
 out:
-	mutex_unlock(&fi->ais_lock);
+	spin_unlock_irqrestore(&fi->ais_lock, flags);
 	return ret;
 }
 
@@ -2702,6 +2707,8 @@ static int flic_inject_airq(struct kvm *kvm, struct kvm_device_attr *attr)
 	unsigned int id = attr->attr;
 	struct s390_io_adapter *adapter = get_io_adapter(kvm, id);
 
+	kvm->stat.io_flic_inject_airq++;
+
 	if (!adapter)
 		return -EINVAL;
 
@@ -2712,6 +2719,7 @@ static int flic_ais_mode_set_all(struct kvm *kvm, struct kvm_device_attr *attr)
 {
 	struct kvm_s390_float_interrupt *fi = &kvm->arch.float_int;
 	struct kvm_s390_ais_all ais;
+	unsigned long flags;
 
 	if (!test_kvm_facility(kvm, 72))
 		return -EOPNOTSUPP;
@@ -2719,10 +2727,10 @@ static int flic_ais_mode_set_all(struct kvm *kvm, struct kvm_device_attr *attr)
 	if (copy_from_user(&ais, (void __user *)attr->addr, sizeof(ais)))
 		return -EFAULT;
 
-	mutex_lock(&fi->ais_lock);
+	spin_lock_irqsave(&fi->ais_lock, flags);
 	fi->simm = ais.simm;
 	fi->nimm = ais.nimm;
-	mutex_unlock(&fi->ais_lock);
+	spin_unlock_irqrestore(&fi->ais_lock, flags);
 
 	return 0;
 }
@@ -2865,9 +2873,12 @@ static int adapter_indicators_set(struct kvm *kvm,
 	struct s390_map_info *ind_info, *summary_info;
 	void *map;
 	struct page *ind_page, *summary_page;
+	unsigned long flags;
 
+	spin_lock_irqsave(&adapter->maps_lock, flags);
 	ind_info = get_map_info(adapter, adapter_int->ind_addr);
 	if (!ind_info) {
+		spin_unlock_irqrestore(&adapter->maps_lock, flags);
 		ind_page = get_map_page(kvm, adapter_int->ind_addr);
 		if (!ind_page)
 			return -1;
@@ -2883,9 +2894,13 @@ static int adapter_indicators_set(struct kvm *kvm,
 		map = page_address(ind_info->page);
 		bit = get_ind_bit(ind_info->addr, adapter_int->ind_offset, adapter->swap);
 		set_bit(bit, map);
+		spin_unlock_irqrestore(&adapter->maps_lock, flags);
 	}
+
+	spin_lock_irqsave(&adapter->maps_lock, flags);
 	summary_info = get_map_info(adapter, adapter_int->summary_addr);
 	if (!summary_info) {
+		spin_unlock_irqrestore(&adapter->maps_lock, flags);
 		summary_page = get_map_page(kvm, adapter_int->summary_addr);
 		if (!summary_page) {
 			put_page(ind_page);
@@ -2904,6 +2919,7 @@ static int adapter_indicators_set(struct kvm *kvm,
 		bit = get_ind_bit(summary_info->addr, adapter_int->summary_offset,
 				  adapter->swap);
 		summary_set = test_and_set_bit(bit, map);
+		spin_unlock_irqrestore(&adapter->maps_lock, flags);
 	}
 
 	if (!ind_info)
@@ -2913,6 +2929,37 @@ static int adapter_indicators_set(struct kvm *kvm,
 	return summary_set ? 0 : 1;
 }
 
+static int adapter_indicators_set_fast(struct kvm *kvm,
+				       struct s390_io_adapter *adapter,
+				       struct kvm_s390_adapter_int *adapter_int)
+{
+	unsigned long bit;
+	int summary_set;
+	struct s390_map_info *ind_info, *summary_info;
+	void *map;
+
+	spin_lock(&adapter->maps_lock);
+	ind_info = get_map_info(adapter, adapter_int->ind_addr);
+	if (!ind_info) {
+		spin_unlock(&adapter->maps_lock);
+		return -EWOULDBLOCK;
+	}
+	map = page_address(ind_info->page);
+	bit = get_ind_bit(ind_info->addr, adapter_int->ind_offset, adapter->swap);
+	set_bit(bit, map);
+	summary_info = get_map_info(adapter, adapter_int->summary_addr);
+	if (!summary_info) {
+		spin_unlock(&adapter->maps_lock);
+		return -EWOULDBLOCK;
+	}
+	map = page_address(summary_info->page);
+	bit = get_ind_bit(summary_info->addr, adapter_int->summary_offset,
+			  adapter->swap);
+	summary_set = test_and_set_bit(bit, map);
+	spin_unlock(&adapter->maps_lock);
+	return summary_set ? 0 : 1;
+}
+
 /*
  * < 0 - not injected due to error
  * = 0 - coalesced, summary indicator already active
@@ -2924,7 +2971,8 @@ static int set_adapter_int(struct kvm_kernel_irq_routing_entry *e,
 {
 	int ret;
 	struct s390_io_adapter *adapter;
-	unsigned long flags;
+
+	kvm->stat.io_set_adapter_int++;
 
 	/* We're only interested in the 0->1 transition. */
 	if (!level)
@@ -2932,9 +2980,7 @@ static int set_adapter_int(struct kvm_kernel_irq_routing_entry *e,
 	adapter = get_io_adapter(kvm, e->adapter.adapter_id);
 	if (!adapter)
 		return -1;
-	spin_lock_irqsave(&adapter->maps_lock, flags);
 	ret = adapter_indicators_set(kvm, adapter, &e->adapter);
-	spin_unlock_irqrestore(&adapter->maps_lock, flags);
 	if ((ret > 0) && !adapter->masked) {
 		ret = kvm_s390_inject_airq(kvm, adapter);
 		if (ret == 0)
@@ -2996,7 +3042,6 @@ int kvm_set_routing_entry(struct kvm *kvm,
 	int idx;
 
 	switch (ue->type) {
-	/* we store the userspace addresses instead of the guest addresses */
 	case KVM_IRQ_ROUTING_S390_ADAPTER:
 		if (kvm_is_ucontrol(kvm))
 			return -EINVAL;
@@ -3587,3 +3632,72 @@ int __init kvm_s390_gib_init(u8 nisc)
 out:
 	return rc;
 }
+
+/*
+ * kvm_arch_set_irq_inatomic: fast-path for irqfd injection
+ */
+int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
+			      struct kvm *kvm, int irq_source_id, int level,
+			      bool line_status)
+{
+	int ret;
+	struct s390_io_adapter *adapter;
+	struct kvm_s390_float_interrupt *fi = &kvm->arch.float_int;
+	struct kvm_s390_interrupt_info *inti;
+	struct kvm_s390_interrupt s390int = {
+			.type = KVM_S390_INT_IO(1, 0, 0, 0),
+			.parm = 0,
+	};
+
+	kvm->stat.io_390_inatomic++;
+
+	/* We're only interested in the 0->1 transition. */
+	if (!level)
+		return -EWOULDBLOCK;
+	if (e->type != KVM_IRQ_ROUTING_S390_ADAPTER)
+		return -EWOULDBLOCK;
+
+	adapter = get_io_adapter(kvm, e->adapter.adapter_id);
+	if (!adapter)
+		return -EWOULDBLOCK;
+
+	s390int.parm64 = isc_to_int_word(adapter->isc);
+	ret = adapter_indicators_set_fast(kvm, adapter, &e->adapter);
+	if (ret < 0)
+		return -EWOULDBLOCK;
+	if (!ret || adapter->masked) {
+		kvm->stat.io_390_inatomic_adapter_masked++;
+		return 0;
+	}
+
+	inti = kzalloc_obj(*inti, GFP_ATOMIC);
+	if (!inti)
+		return -EWOULDBLOCK;
+
+	if (!test_kvm_facility(kvm, 72) || !adapter->suppressible) {
+		ret = kvm_s390_inject_vm(kvm, &s390int, inti);
+			if (ret == 0)
+				return ret;
+			else
+				return -EWOULDBLOCK;
+		}
+
+	spin_lock(&fi->ais_lock);
+	if (fi->nimm & AIS_MODE_MASK(adapter->isc)) {
+		trace_kvm_s390_airq_suppressed(adapter->id, adapter->isc);
+		kfree(inti);
+		goto out;
+	}
+
+	ret = kvm_s390_inject_vm(kvm, &s390int, inti);
+	if (!ret && (fi->simm & AIS_MODE_MASK(adapter->isc))) {
+		fi->nimm |= AIS_MODE_MASK(adapter->isc);
+		trace_kvm_s390_modify_ais_mode(adapter->isc,
+					       KVM_S390_AIS_MODE_SINGLE, 2);
+	}
+	goto out;
+
+out:
+	spin_unlock(&fi->ais_lock);
+	return 0;
+}
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 4b1820bcead1..c53e25bcfab4 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -70,6 +70,10 @@ const struct kvm_stats_desc kvm_vm_stats_desc[] = {
 	STATS_DESC_COUNTER(VM, inject_io),
 	STATS_DESC_COUNTER(VM, io_390_adapter_map),
 	STATS_DESC_COUNTER(VM, io_390_adapter_unmap),
+	STATS_DESC_COUNTER(VM, io_390_inatomic),
+	STATS_DESC_COUNTER(VM, io_flic_inject_airq),
+	STATS_DESC_COUNTER(VM, io_set_adapter_int),
+	STATS_DESC_COUNTER(VM, io_390_inatomic_adapter_masked),
 	STATS_DESC_COUNTER(VM, inject_float_mchk),
 	STATS_DESC_COUNTER(VM, inject_pfault_done),
 	STATS_DESC_COUNTER(VM, inject_service_signal),
@@ -2862,6 +2866,7 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 	void __user *argp = (void __user *)arg;
 	struct kvm_device_attr attr;
 	int r;
+	struct kvm_s390_interrupt_info *inti;
 
 	switch (ioctl) {
 	case KVM_S390_INTERRUPT: {
@@ -2870,7 +2875,10 @@ int kvm_arch_vm_ioctl(struct file *filp, unsigned int ioctl, unsigned long arg)
 		r = -EFAULT;
 		if (copy_from_user(&s390int, argp, sizeof(s390int)))
 			break;
-		r = kvm_s390_inject_vm(kvm, &s390int);
+		inti = kzalloc_obj(*inti, GFP_KERNEL_ACCOUNT);
+		if (!inti)
+			return -ENOMEM;
+		r = kvm_s390_inject_vm(kvm, &s390int, inti);
 		break;
 	}
 	case KVM_CREATE_IRQCHIP: {
@@ -3268,7 +3276,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 		mutex_unlock(&kvm->lock);
 	}
 
-	mutex_init(&kvm->arch.float_int.ais_lock);
+	spin_lock_init(&kvm->arch.float_int.ais_lock);
 	spin_lock_init(&kvm->arch.float_int.lock);
 	for (i = 0; i < FIRQ_LIST_COUNT; i++)
 		INIT_LIST_HEAD(&kvm->arch.float_int.lists[i]);
@@ -4389,11 +4397,16 @@ int kvm_s390_try_set_tod_clock(struct kvm *kvm, const struct kvm_s390_vm_tod_clo
 	return 1;
 }
 
-static void __kvm_inject_pfault_token(struct kvm_vcpu *vcpu, bool start_token,
-				      unsigned long token)
+static int __kvm_inject_pfault_token(struct kvm_vcpu *vcpu, bool start_token,
+				     unsigned long token)
 {
 	struct kvm_s390_interrupt inti;
 	struct kvm_s390_irq irq;
+	struct kvm_s390_interrupt_info *inti_mem;
+
+	inti_mem = kzalloc_obj(*inti_mem, GFP_KERNEL_ACCOUNT);
+	if (!inti_mem)
+		return -ENOMEM;
 
 	if (start_token) {
 		irq.u.ext.ext_params2 = token;
@@ -4402,8 +4415,9 @@ static void __kvm_inject_pfault_token(struct kvm_vcpu *vcpu, bool start_token,
 	} else {
 		inti.type = KVM_S390_INT_PFAULT_DONE;
 		inti.parm64 = token;
-		WARN_ON_ONCE(kvm_s390_inject_vm(vcpu->kvm, &inti));
+		WARN_ON_ONCE(kvm_s390_inject_vm(vcpu->kvm, &inti, inti_mem));
 	}
+	return true;
 }
 
 bool kvm_arch_async_page_not_present(struct kvm_vcpu *vcpu,
diff --git a/arch/s390/kvm/kvm-s390.h b/arch/s390/kvm/kvm-s390.h
index bf1d7798c1af..2f2da868a040 100644
--- a/arch/s390/kvm/kvm-s390.h
+++ b/arch/s390/kvm/kvm-s390.h
@@ -373,7 +373,8 @@ int __must_check kvm_s390_deliver_pending_interrupts(struct kvm_vcpu *vcpu);
 void kvm_s390_clear_local_irqs(struct kvm_vcpu *vcpu);
 void kvm_s390_clear_float_irqs(struct kvm *kvm);
 int __must_check kvm_s390_inject_vm(struct kvm *kvm,
-				    struct kvm_s390_interrupt *s390int);
+				    struct kvm_s390_interrupt *s390int,
+				    struct kvm_s390_interrupt_info *inti);
 int __must_check kvm_s390_inject_vcpu(struct kvm_vcpu *vcpu,
 				      struct kvm_s390_irq *irq);
 static inline int kvm_s390_inject_prog_irq(struct kvm_vcpu *vcpu,
-- 
2.52.0

On 3/25/26 9:42 PM, Douglas Freimuth wrote:

> @@ -1963,15 +1963,10 @@ static int __inject_vm(struct kvm *kvm, struct kvm_s390_interrupt_info *inti)
>  }
>  
>  int kvm_s390_inject_vm(struct kvm *kvm,
> -		       struct kvm_s390_interrupt *s390int)
> +		       struct kvm_s390_interrupt *s390int, struct kvm_s390_interrupt_info *inti)

Sashiko makes a point here, sort of.

I believe it's wrong in the sense that you still left the code in this
function that frees inti on error paths, effectively freeing it under
the exact same circumstances as before this patch when it was allocated
in kvm_s390_inject_vm.

But now that you have moved allocation of inti to be the responsibility
of the caller of kvm_s390_inject_vm it generally would imply that the
caller should ALSO be responsible for freeing that memory.  But now both
the passing case and the failing case have given up control of that
memory and assume it's taken care of.

I think that's worth a comment explaining it.

[...]

> +/*
> + * kvm_arch_set_irq_inatomic: fast-path for irqfd injection
> + */
> +int kvm_arch_set_irq_inatomic(struct kvm_kernel_irq_routing_entry *e,
> +			      struct kvm *kvm, int irq_source_id, int level,
> +			      bool line_status)
> +{
> +	int ret;
> +	struct s390_io_adapter *adapter;
> +	struct kvm_s390_float_interrupt *fi = &kvm->arch.float_int;
> +	struct kvm_s390_interrupt_info *inti;
> +	struct kvm_s390_interrupt s390int = {
> +			.type = KVM_S390_INT_IO(1, 0, 0, 0),
> +			.parm = 0,
> +	};
> +
> +	kvm->stat.io_390_inatomic++;
> +
> +	/* We're only interested in the 0->1 transition. */
> +	if (!level)
> +		return -EWOULDBLOCK;
> +	if (e->type != KVM_IRQ_ROUTING_S390_ADAPTER)
> +		return -EWOULDBLOCK;
> +
> +	adapter = get_io_adapter(kvm, e->adapter.adapter_id);
> +	if (!adapter)
> +		return -EWOULDBLOCK;
> +
> +	s390int.parm64 = isc_to_int_word(adapter->isc);
> +	ret = adapter_indicators_set_fast(kvm, adapter, &e->adapter);

Sashiko asks an interesting question around this point.  I think it's a
bit more broad than it states, however:

What happens if we -EWOULDBLOCK for any reason past this point and
adapter_indicators_set_fast above here has set the summary bit.

If we then fall back to the 'slow path' and the code in
adapter_indicators_set(), we could possibly see the summary bit was
already set (by adapter_indicators_set_fast() above) and assume that we
don't need to inject anything because the thread of executing that set
the summary bit ALSO did the inject.  But in this particular case we
actually never did.

Do we need to unset the summary bit for these subsequent -EWOULDBLOCK
cases so that the subsequent fallback path will know it must inject?
But we should only undo this if adapter_indicators_set_fast() actually
set the summary bit in the first place.
The indicator bits themselves that might have been set by
adapter_indicators_set_fast() should be fine to leave on, injection
decision is based on the setting of the summary indicator.

> +	if (ret < 0)
> +		return -EWOULDBLOCK;
> +	if (!ret || adapter->masked) {
> +		kvm->stat.io_390_inatomic_adapter_masked++;
> +		return 0;
> +	}
> +
> +	inti = kzalloc_obj(*inti, GFP_ATOMIC);
> +	if (!inti)
> +		return -EWOULDBLOCK;
> +
> +	if (!test_kvm_facility(kvm, 72) || !adapter->suppressible) {
> +		ret = kvm_s390_inject_vm(kvm, &s390int, inti);
> +			if (ret == 0)
> +				return ret;
> +			else
> +				return -EWOULDBLOCK;
> +		}
> +
> +	spin_lock(&fi->ais_lock);
> +	if (fi->nimm & AIS_MODE_MASK(adapter->isc)) {
> +		trace_kvm_s390_airq_suppressed(adapter->id, adapter->isc);
> +		kfree(inti);
> +		goto out;
> +	}
> +
> +	ret = kvm_s390_inject_vm(kvm, &s390int, inti);
> +	if (!ret && (fi->simm & AIS_MODE_MASK(adapter->isc))) {
> +		fi->nimm |= AIS_MODE_MASK(adapter->isc);
> +		trace_kvm_s390_modify_ais_mode(adapter->isc,
> +					       KVM_S390_AIS_MODE_SINGLE, 2);
> +	}
> +	goto out;

Goto is unncessary here.

Also, you don't check returns from kvm_s390_inject_vm on this path?  If
any errors we still return 0 to caller (compare this to the call above
where any errors would instead yield -EWOULDBLOCK)  Can you please
double check this?

[...]

>  
> -static void __kvm_inject_pfault_token(struct kvm_vcpu *vcpu, bool start_token,
> -				      unsigned long token)
> +static int __kvm_inject_pfault_token(struct kvm_vcpu *vcpu, bool start_token,
> +				     unsigned long token)

You updated this to return a value but AFAICT you never update the
callers of this function to actually handle the return value.