[PATCH v2 5/6] kvm: KVM_EOIFD, an eventfd for EOIs

[Alex Williamson <alex.williamson@redhat.com>]

This new ioctl enables an eventfd to be triggered when an EOI is
written for a specified irqchip pin.  By default this is a simple
notification, but we can also tie the eoifd to a level irqfd, which
enables the irqchip pin to be automatically de-asserted on EOI.
This mode is particularly useful for device-assignment applications
where the unmask and notify triggers a hardware unmask.  The default
mode is most applicable to simple notify with no side-effects for
userspace usage, such as Qemu.

Here we make use of the reference counting of the _irq_source
object allowing us to share it with an irqfd and cleanup regardless
of the release order.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
---

 Documentation/virtual/kvm/api.txt |   24 +++++
 arch/x86/kvm/x86.c                |    1 
 include/linux/kvm.h               |   14 +++
 include/linux/kvm_host.h          |   13 +++
 virt/kvm/eventfd.c                |  189 +++++++++++++++++++++++++++++++++++++
 virt/kvm/kvm_main.c               |   11 ++
 6 files changed, 250 insertions(+), 2 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index b216709..87a2558 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1987,6 +1987,30 @@ interrupts with those injected through KVM_IRQ_LINE.  IRQFDs created
 with KVM_IRQFD_FLAG_LEVEL must also set this flag when de-assiging.
 KVM_IRQFD_FLAG_LEVEL support is indicated by KVM_CAP_IRQFD_LEVEL.
 
+4.77 KVM_EOIFD
+
+Capability: KVM_CAP_EOIFD
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_eoifd (in)
+Returns: 0 on success, -1 on error
+
+KVM_EOIFD allows userspace to receive EOI notification through an
+eventfd for level triggered irqchip interrupts.  Behavior for edge
+triggered interrupts is undefined.  kvm_eoifd.fd specifies the eventfd
+used for notification and kvm_eoifd.gsi specifies the irchip pin,
+similar to KVM_IRQFD.  KVM_EOIFD_FLAG_DEASSIGN is used to deassign
+a previously enabled eoifd and should also set fd and gsi to match.
+
+The KVM_EOIFD_FLAG_LEVEL_IRQFD flag indicates that the EOI is for
+a level triggered EOI and the kvm_eoifd structure includes
+kvm_eoifd.irqfd, which must be previously configured using KVM_IRQFD
+with the KVM_IRQFD_FLAG_LEVEL flag.  This allows both EOI notification
+through kvm_eoifd.fd as well as automatically de-asserting level
+irqfds on EOI.  Both KVM_EOIFD_FLAG_DEASSIGN and
+KVM_EOIFD_FLAG_LEVEL_IRQFD should be used to de-assign an eoifd
+initially setup with KVM_EOIFD_FLAG_LEVEL_IRQFD.
+
 5. The kvm_run structure
 ------------------------
 
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 80bed07..62d6eca 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2149,6 +2149,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_PCI_2_3:
 	case KVM_CAP_KVMCLOCK_CTRL:
 	case KVM_CAP_IRQFD_LEVEL:
+	case KVM_CAP_EOIFD:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index b2e6e4f..7567e7d 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -619,6 +619,7 @@ struct kvm_ppc_smmu_info {
 #define KVM_CAP_S390_COW 79
 #define KVM_CAP_PPC_ALLOC_HTAB 80
 #define KVM_CAP_IRQFD_LEVEL 81
+#define KVM_CAP_EOIFD 82
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -694,6 +695,17 @@ struct kvm_irqfd {
 	__u8  pad[20];
 };
 
+#define KVM_EOIFD_FLAG_DEASSIGN (1 << 0)
+#define KVM_EOIFD_FLAG_LEVEL_IRQFD (1 << 1)
+
+struct kvm_eoifd {
+	__u32 fd;
+	__u32 gsi;
+	__u32 flags;
+	__u32 irqfd;
+	__u8 pad[16];
+};
+
 struct kvm_clock_data {
 	__u64 clock;
 	__u32 flags;
@@ -834,6 +846,8 @@ struct kvm_s390_ucas_mapping {
 #define KVM_PPC_GET_SMMU_INFO	  _IOR(KVMIO,  0xa6, struct kvm_ppc_smmu_info)
 /* Available with KVM_CAP_PPC_ALLOC_HTAB */
 #define KVM_PPC_ALLOCATE_HTAB	  _IOWR(KVMIO, 0xa7, __u32)
+/* Available with KVM_CAP_EOIFD */
+#define KVM_EOIFD                 _IOW(KVMIO,  0xa8, struct kvm_eoifd)
 
 /*
  * ioctls for vcpu fds
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index ae3b426..83472eb 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -285,6 +285,10 @@ struct kvm {
 		struct list_head  items;
 	} irqfds;
 	struct list_head ioeventfds;
+	struct {
+		spinlock_t        lock;
+		struct list_head  items;
+	} eoifds;
 #endif
 	struct kvm_vm_stat stat;
 	struct kvm_arch arch;
@@ -828,6 +832,8 @@ int kvm_irqfd(struct kvm *kvm, struct kvm_irqfd *args);
 void kvm_irqfd_release(struct kvm *kvm);
 void kvm_irq_routing_update(struct kvm *, struct kvm_irq_routing_table *);
 int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args);
+int kvm_eoifd(struct kvm *kvm, struct kvm_eoifd *args);
+void kvm_eoifd_release(struct kvm *kvm);
 
 #else
 
@@ -853,6 +859,13 @@ static inline int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 	return -ENOSYS;
 }
 
+static inline int kvm_eoifd(struct kvm *kvm, struct kvm_eoifd *args)
+{
+	return -ENOSYS;
+}
+
+static inline void kvm_eoifd_release(struct kvm *kvm) {}
+
 #endif /* CONFIG_HAVE_KVM_EVENTFD */
 
 #ifdef CONFIG_KVM_APIC_ARCHITECTURE
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 18cc284..02ca50f 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -62,8 +62,7 @@ static void put_irq_source(struct _irq_source *source)
 		kref_put(&source->kref, release_irq_source);
 }
 
-static struct _irq_source *__attribute__ ((used)) /* white lie for now */
-get_irq_source(struct _irq_source *source)
+static struct _irq_source *get_irq_source(struct _irq_source *source)
 {
 	if (source)
 		kref_get(&source->kref);
@@ -118,6 +117,41 @@ struct _irqfd {
 	struct work_struct shutdown;
 };
 
+static struct _irq_source *get_irq_source_from_irqfd(struct kvm *kvm, int fd)
+{
+	struct file *file;
+	struct eventfd_ctx *eventfd;
+	struct _irqfd *irqfd;
+	struct _irq_source *source = NULL;
+
+	file = fget(fd);
+	if (!file)
+		return ERR_PTR(-EBADF);
+
+	eventfd = eventfd_ctx_fileget(file);
+	if (IS_ERR(eventfd)) {
+		fput(file);
+		return (struct _irq_source *)eventfd;
+	}
+
+	spin_lock_irq(&kvm->irqfds.lock);
+
+	list_for_each_entry(irqfd, &kvm->irqfds.items, list) {
+		if (irqfd->eventfd != eventfd)
+			continue;
+
+		source = get_irq_source(irqfd->source);
+		break;
+	}
+
+	spin_unlock_irq(&kvm->irqfds.lock);
+
+	eventfd_ctx_put(eventfd);
+	fput(file);
+
+	return source ? source : ERR_PTR(-ENODEV);
+}
+
 static struct workqueue_struct *irqfd_cleanup_wq;
 
 static void
@@ -375,6 +409,8 @@ kvm_eventfd_init(struct kvm *kvm)
 	spin_lock_init(&kvm->irqfds.lock);
 	INIT_LIST_HEAD(&kvm->irqfds.items);
 	INIT_LIST_HEAD(&kvm->ioeventfds);
+	spin_lock_init(&kvm->eoifds.lock);
+	INIT_LIST_HEAD(&kvm->eoifds.items);
 }
 
 /*
@@ -743,3 +779,152 @@ kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
 
 	return kvm_assign_ioeventfd(kvm, args);
 }
+
+/*
+ * --------------------------------------------------------------------
+ *  eoifd: Translate KVM APIC/IOAPIC EOI into eventfd signal.
+ *
+ *  userspace can register GSIs with an eventfd for receiving
+ *  notification when an EOI occurs.
+ * --------------------------------------------------------------------
+ */
+
+struct _eoifd {
+	struct kvm *kvm;
+	struct eventfd_ctx *eventfd;
+	struct _irq_source *source;
+	struct kvm_irq_ack_notifier notifier;
+	struct list_head list;
+};
+
+static void eoifd_event(struct kvm_irq_ack_notifier *notifier)
+{
+	struct _eoifd *eoifd;
+
+	eoifd = container_of(notifier, struct _eoifd, notifier);
+
+	if (eoifd->source)
+		kvm_set_irq(eoifd->kvm, eoifd->source->id,
+			    eoifd->notifier.gsi, 0);
+
+	eventfd_signal(eoifd->eventfd, 1);
+}
+
+static int kvm_assign_eoifd(struct kvm *kvm, struct kvm_eoifd *args)
+{
+	struct eventfd_ctx *eventfd;
+	struct _eoifd *eoifd, *tmp;
+	struct _irq_source *source = NULL;
+
+	if (args->flags & KVM_EOIFD_FLAG_LEVEL_IRQFD) {
+		source = get_irq_source_from_irqfd(kvm, args->irqfd);
+		if (IS_ERR(source))
+			return PTR_ERR(source);
+	}
+
+	eventfd = eventfd_ctx_fdget(args->fd);
+	if (IS_ERR(eventfd)) {
+		put_irq_source(source);
+		return PTR_ERR(eventfd);
+	}
+
+	eoifd = kzalloc(sizeof(*eoifd), GFP_KERNEL);
+	if (!eoifd) {
+		put_irq_source(source);
+		eventfd_ctx_put(eventfd);
+		return -ENOMEM;
+	}
+
+	INIT_LIST_HEAD(&eoifd->list);
+	eoifd->kvm = kvm;
+	eoifd->eventfd = eventfd;
+	eoifd->source = source;
+	eoifd->notifier.gsi = args->gsi;
+	eoifd->notifier.irq_acked = eoifd_event;
+
+	spin_lock_irq(&kvm->eoifds.lock);
+
+	list_for_each_entry(tmp, &kvm->eoifds.items, list) {
+		if (eoifd->eventfd != tmp->eventfd)
+			continue;
+
+		put_irq_source(source);
+		eventfd_ctx_put(eventfd);
+		kfree(eoifd);
+		return -EBUSY;
+	}
+
+	list_add_tail(&eoifd->list, &kvm->eoifds.items);
+	kvm_register_irq_ack_notifier(kvm, &eoifd->notifier);
+
+	spin_unlock_irq(&kvm->eoifds.lock);
+
+	return 0;
+}
+
+static void eoifd_deactivate(struct kvm *kvm, struct _eoifd *eoifd)
+{
+	list_del(&eoifd->list);
+	kvm_unregister_irq_ack_notifier(kvm, &eoifd->notifier);
+	put_irq_source(eoifd->source);
+	eventfd_ctx_put(eoifd->eventfd);
+	kfree(eoifd);
+}
+
+void kvm_eoifd_release(struct kvm *kvm)
+{
+	struct _eoifd *eoifd, *tmp;
+
+	spin_lock_irq(&kvm->eoifds.lock);
+
+	list_for_each_entry_safe(eoifd, tmp, &kvm->eoifds.items, list)
+		eoifd_deactivate(kvm, eoifd);
+
+	spin_unlock_irq(&kvm->eoifds.lock);
+}
+
+static int kvm_deassign_eoifd(struct kvm *kvm, struct kvm_eoifd *args)
+{
+	struct eventfd_ctx *eventfd;
+	struct _eoifd *eoifd;
+	bool uses_source = (args->flags & KVM_EOIFD_FLAG_LEVEL_IRQFD) != 0;
+	int ret = -ENODEV;
+
+	eventfd = eventfd_ctx_fdget(args->fd);
+	if (IS_ERR(eventfd))
+		return PTR_ERR(eventfd);
+
+	spin_lock_irq(&kvm->eoifds.lock);
+
+	list_for_each_entry(eoifd, &kvm->eoifds.items, list) {
+		/*
+		 * Matching eventfd is unique since we don't allow dulicates,
+		 * the rest is sanitizing the calling parameters.
+		 */
+		if (eoifd->eventfd == eventfd &&
+		    eoifd->notifier.gsi == args->gsi &&
+		    uses_source == (eoifd->source != NULL)) {
+			eoifd_deactivate(kvm, eoifd);
+			ret = 0;
+			break;
+		}
+	}
+
+	spin_unlock_irq(&kvm->eoifds.lock);
+
+	eventfd_ctx_put(eventfd);
+
+	return ret;
+}
+
+int kvm_eoifd(struct kvm *kvm, struct kvm_eoifd *args)
+{
+	if (args->flags & ~(KVM_EOIFD_FLAG_DEASSIGN |
+			    KVM_EOIFD_FLAG_LEVEL_IRQFD))
+		return -EINVAL;
+
+	if (args->flags & KVM_EOIFD_FLAG_DEASSIGN)
+		return kvm_deassign_eoifd(kvm, args);
+
+	return kvm_assign_eoifd(kvm, args);
+}
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index b4ad14cc..5b41df1 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -620,6 +620,8 @@ static int kvm_vm_release(struct inode *inode, struct file *filp)
 
 	kvm_irqfd_release(kvm);
 
+	kvm_eoifd_release(kvm);
+
 	kvm_put_kvm(kvm);
 	return 0;
 }
@@ -2093,6 +2095,15 @@ static long kvm_vm_ioctl(struct file *filp,
 		break;
 	}
 #endif
+	case KVM_EOIFD: {
+		struct kvm_eoifd data;
+
+		r = -EFAULT;
+		if (copy_from_user(&data, argp, sizeof data))
+			goto out;
+		r = kvm_eoifd(kvm, &data);
+		break;
+	}
 	default:
 		r = kvm_arch_vm_ioctl(filp, ioctl, arg);
 		if (r == -ENOTTY)