Date:	Tue, 21 Aug 2012 13:29:14 -0600
From:	Alex Williamson <alex.williamson@...hat.com>
To:	avi@...hat.com, mst@...hat.com
Cc:	gleb@...hat.com, kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v9 2/2] kvm: On Ack, De-assert & Notify KVM_IRQFD extension

For VFIO based device assignment we'd like a mechanism to allow level
triggered interrutps to be directly injected into KVM.  KVM_IRQFD
already allows this for edge triggered interrupts, but for level, we
need to watch for acknowledgement of the interrupt from the guest to
provide us a hint when to test the device and allow it to re-assert
if necessary.  To do this, we create a new KVM_IRQFD mode called
"On Ack, De-assert & Notify", or OADN.  In this mode, an interrupt
injection provides only a gsi assertion.  We then hook into the IRQ
ACK notifier, which when triggered de-asserts the gsi and notifies
via another eventfd.  It's then the responsibility of the user to
re-assert the interrupt is service is still required.

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

 Documentation/virtual/kvm/api.txt |   13 ++
 arch/x86/kvm/x86.c                |    1 
 include/linux/kvm.h               |    6 +
 include/linux/kvm_host.h          |    1 
 virt/kvm/eventfd.c                |  193 ++++++++++++++++++++++++++++++++++++-
 5 files changed, 210 insertions(+), 4 deletions(-)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index bf33aaa..87d7321 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1946,6 +1946,19 @@ the guest using the specified gsi pin.  The irqfd is removed using
 the KVM_IRQFD_FLAG_DEASSIGN flag, specifying both kvm_irqfd.fd
 and kvm_irqfd.gsi.
 
+With KVM_CAP_IRQFD_OADN, KVM_IRQFD supports an "On Ack, De-assert &
+Notify" option that allows emulation of level-triggered interrupts.
+When kvm_irqfd.fd is triggered, the requested gsi is asserted and
+remains asserted until interaction with the irqchip indicates the
+VM has acknowledged the interrupt, such as an EOI.  On acknoledgement
+the gsi is automatically de-asserted and the user is notified via
+kvm_irqfd.notifyfd.  The user is then required to re-assert the
+interrupt if the associated device still requires service.  To enable
+this mode, configure the KVM_IRQFD using the KVM_IRQFD_FLAG_OADN flag
+and specify kvm_irqfd.notifyfd.  Note that closing kvm_irqfd.notifyfd
+while configured in this mode does not disable the irqfd.  The
+KVM_IRQFD_FLAG_OADN flag is only necessary on assignment.
+
 4.76 KVM_PPC_ALLOCATE_HTAB
 
 Capability: KVM_CAP_PPC_ALLOC_HTAB
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cd98673..fde7b66 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2175,6 +2175,7 @@ int kvm_dev_ioctl_check_extension(long ext)
 	case KVM_CAP_PCI_2_3:
 	case KVM_CAP_KVMCLOCK_CTRL:
 	case KVM_CAP_IRQFD_IRQ_SOURCE_ID:
+	case KVM_CAP_IRQFD_OADN:
 		r = 1;
 		break;
 	case KVM_CAP_COALESCED_MMIO:
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index ae66b9c..ec0f1d8 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_IRQ_SOURCE_ID 81
+#define KVM_CAP_IRQFD_OADN 82
 
 #ifdef KVM_CAP_IRQ_ROUTING
 
@@ -684,12 +685,15 @@ struct kvm_xen_hvm_config {
 #endif
 
 #define KVM_IRQFD_FLAG_DEASSIGN (1 << 0)
+/* Availabie with KVM_CAP_IRQFD_OADN */
+#define KVM_IRQFD_FLAG_OADN (1 << 1)
 
 struct kvm_irqfd {
 	__u32 fd;
 	__u32 gsi;
 	__u32 flags;
-	__u8  pad[20];
+	__u32 notifyfd;
+	__u8  pad[16];
 };
 
 struct kvm_clock_data {
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index b763230..d502d08 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -284,6 +284,7 @@ struct kvm {
 	struct {
 		spinlock_t        lock;
 		struct list_head  items;
+		struct list_head  oadns;
 	} irqfds;
 	struct list_head ioeventfds;
 #endif
diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
index 2245cfa..dfdb5b2 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -43,6 +43,23 @@
  * --------------------------------------------------------------------
  */
 
+/*
+ * OADN irqfds (On Ack, De-assert & Notify) are a special variety of
+ * irqfds that assert an interrupt to the irqchip on eventfd trigger,
+ * receieve notification when userspace acknowledges the interrupt,
+ * automatically de-asserts the irqchip level, and notifies userspace
+ * via the oadn_eventfd.  This object helps to provide one-to-many
+ * deassert-to-notify so we can share a single irq source ID per OADN.
+ */
+struct _irqfd_oadn {
+	struct kvm *kvm;
+	int irq_source_id; /* IRQ source ID shared by these irqfds */
+	struct list_head irqfds; /* list of irqfds using this object */
+	struct kvm_irq_ack_notifier notifier; /* IRQ ACK notification */
+	struct kref kref; /* Race-free removal */
+	struct list_head list;
+};
+
 struct _irqfd {
 	/* Used for MSI fast-path */
 	struct kvm *kvm;
@@ -52,6 +69,10 @@ struct _irqfd {
 	/* Used for level IRQ fast-path */
 	int gsi;
 	struct work_struct inject;
+	/* Used for OADN (On Ack, De-assert & Notify) path */
+	struct eventfd_ctx *oadn_eventfd;
+	struct list_head oadn_list;
+	struct _irqfd_oadn *oadn;
 	/* Used for setup/shutdown */
 	struct eventfd_ctx *eventfd;
 	struct list_head list;
@@ -71,6 +92,51 @@ irqfd_inject(struct work_struct *work)
 	kvm_set_irq(kvm, KVM_IRQFD_IRQ_SOURCE_ID, irqfd->gsi, 0);
 }
 
+static void
+irqfd_oadn_inject(struct work_struct *work)
+{
+	struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
+
+	kvm_set_irq(irqfd->kvm, irqfd->oadn->irq_source_id, irqfd->gsi, 1);
+}
+
+/*
+ * Since OADN irqfds share an IRQ source ID, we de-assert once then
+ * notify all of the OADN irqfds using this GSI.  We can't do multiple
+ * de-asserts or we risk racing with incoming re-asserts.
+ */
+static void
+irqfd_oadn_notify(struct kvm_irq_ack_notifier *kian)
+{
+	struct _irqfd_oadn *oadn;
+	struct _irqfd *irqfd;
+
+	oadn = container_of(kian, struct _irqfd_oadn, notifier);
+
+	rcu_read_lock();
+
+	kvm_set_irq(oadn->kvm, oadn->irq_source_id,
+		    oadn->notifier.gsi, 0);
+
+	list_for_each_entry_rcu(irqfd, &oadn->irqfds, oadn_list)
+		eventfd_signal(irqfd->oadn_eventfd, 1);
+
+	rcu_read_unlock();
+}
+
+/*
+ * Assumes kvm->irqfds.lock is held.  Remove from the list of OADNs, new
+ * users will allocate their own, letting us de-assert this GSI on free,
+ * after the RCU grace period.
+ */
+static void
+irqfd_oadn_release(struct kref *kref)
+{
+	struct _irqfd_oadn *oadn = container_of(kref, struct _irqfd_oadn, kref);
+
+	list_del(&oadn->list);
+}
+
 /*
  * Race-free decouple logic (ordering is critical)
  */
@@ -93,6 +159,35 @@ irqfd_shutdown(struct work_struct *work)
 	flush_work_sync(&irqfd->inject);
 
 	/*
+	 * OADN irqfds use an RCU list for lockless de-assert and user
+	 * notification.  Modify the list using RCU under lock and release
+	 * the OADN object.  Since we later free this irqfd, we must wait
+	 * for an RCU grace period.  If the OADN was released, we can then
+	 * unregister the irq ack notifier, free the irq source ID (assuring
+	 * that the GSI is de-asserted), and free the object.
+	 */
+	if (irqfd->oadn) {
+		struct _irqfd_oadn *oadn = irqfd->oadn;
+		struct kvm *kvm = oadn->kvm;
+		bool released;
+
+		spin_lock_irq(&irqfd->kvm->irqfds.lock);
+		list_del_rcu(&irqfd->oadn_list);
+		released = kref_put(&oadn->kref, irqfd_oadn_release);
+		spin_unlock_irq(&irqfd->kvm->irqfds.lock);
+
+		synchronize_rcu();
+
+		if (released) {
+			kvm_unregister_irq_ack_notifier(kvm, &oadn->notifier);
+			kvm_free_irq_source_id(kvm, oadn->irq_source_id);
+			kfree(oadn);
+		}
+
+		eventfd_ctx_put(irqfd->oadn_eventfd);
+	}
+
+	/*
 	 * It is now safe to release the object's resources
 	 */
 	eventfd_ctx_put(irqfd->eventfd);
@@ -202,8 +297,9 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 {
 	struct kvm_irq_routing_table *irq_rt;
 	struct _irqfd *irqfd, *tmp;
+	struct _irqfd_oadn *oadn = NULL;
 	struct file *file = NULL;
-	struct eventfd_ctx *eventfd = NULL;
+	struct eventfd_ctx *eventfd = NULL, *oadn_eventfd = NULL;
 	int ret;
 	unsigned int events;
 
@@ -214,7 +310,49 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 	irqfd->kvm = kvm;
 	irqfd->gsi = args->gsi;
 	INIT_LIST_HEAD(&irqfd->list);
-	INIT_WORK(&irqfd->inject, irqfd_inject);
+	INIT_LIST_HEAD(&irqfd->oadn_list);
+
+	if (args->flags & KVM_IRQFD_FLAG_OADN) {
+		oadn_eventfd = eventfd_ctx_fdget(args->notifyfd);
+		if (IS_ERR(oadn_eventfd)) {
+			ret = PTR_ERR(oadn_eventfd);
+			goto fail;
+		}
+
+		irqfd->oadn_eventfd = oadn_eventfd;
+
+		/*
+		 * We may be able to share an existing OADN, but we won't
+		 * know that until we search under spinlock.  We can't get
+		 * an irq_source_id under spinlock, and we'd prefer not to
+		 * do an atomic allocation, so prep an object here and free
+		 * it if we don't need it.
+		 */
+		oadn = kzalloc(sizeof(*oadn), GFP_KERNEL);
+		if (!oadn) {
+			ret = -ENOMEM;
+			goto fail;
+		}
+
+		oadn->kvm = kvm;
+		INIT_LIST_HEAD(&oadn->irqfds);
+		oadn->notifier.gsi = irqfd->gsi;
+		oadn->notifier.irq_acked = irqfd_oadn_notify;
+		kref_init(&oadn->kref);
+		INIT_LIST_HEAD(&oadn->list);
+
+		oadn->irq_source_id = kvm_request_irq_source_id(kvm);
+		if (oadn->irq_source_id < 0) {
+			ret = oadn->irq_source_id;
+			goto fail;
+		}
+
+		irqfd->oadn = oadn;
+
+		INIT_WORK(&irqfd->inject, irqfd_oadn_inject);
+	} else
+		INIT_WORK(&irqfd->inject, irqfd_inject);
+
 	INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
 
 	file = eventfd_fget(args->fd);
@@ -250,6 +388,27 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 		goto fail;
 	}
 
+	/*
+	 * When configuring an OADN irqfd, try to re-use an existing OADN.
+	 */
+	if (oadn) {
+		struct _irqfd_oadn *oadn_tmp;
+
+		list_for_each_entry(oadn_tmp, &kvm->irqfds.oadns, list) {
+			if (oadn_tmp->notifier.gsi == irqfd->gsi) {
+				irqfd->oadn = oadn_tmp;
+				break;
+			}
+		}
+
+		if (irqfd->oadn != oadn)
+			kref_get(&irqfd->oadn->kref);
+		else
+			list_add(&oadn->list, &kvm->irqfds.oadns);
+
+		list_add_rcu(&irqfd->oadn_list, &irqfd->oadn->irqfds);
+	}
+
 	irq_rt = rcu_dereference_protected(kvm->irq_routing,
 					   lockdep_is_held(&kvm->irqfds.lock));
 	irqfd_update(kvm, irqfd, irq_rt);
@@ -267,6 +426,26 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 
 	spin_unlock_irq(&kvm->irqfds.lock);
 
+	if (oadn) {
+		synchronize_rcu();
+
+		/*
+		 * If we weren't able to re-use an OADN, setup the irq ack
+		 * notifier outside of spinlock.  Our interface requires
+		 * users to be able to handle spurious de-assert & notifies,
+		 * so trigger one here to make sure we didn't miss anything.
+		 * Cleanup unused OADN if we share.
+		 */
+		if (irqfd->oadn == oadn)
+			kvm_register_irq_ack_notifier(kvm, &oadn->notifier);
+		else {
+			kvm_free_irq_source_id(kvm, oadn->irq_source_id);
+			kfree(oadn);
+		}
+
+		irqfd_oadn_notify(&irqfd->oadn->notifier);
+	}
+
 	/*
 	 * do not drop the file until the irqfd is fully initialized, otherwise
 	 * we might race against the POLLHUP
@@ -276,12 +455,19 @@ kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
 	return 0;
 
 fail:
+	if (oadn_eventfd && !IS_ERR(oadn_eventfd))
+		eventfd_ctx_put(oadn_eventfd);
+
+	if (oadn && oadn->irq_source_id >= 0)
+		kvm_free_irq_source_id(kvm, oadn->irq_source_id);
+
 	if (eventfd && !IS_ERR(eventfd))
 		eventfd_ctx_put(eventfd);
 
 	if (!IS_ERR(file))
 		fput(file);
 
+	kfree(oadn);
 	kfree(irqfd);
 	return ret;
 }
@@ -291,6 +477,7 @@ kvm_eventfd_init(struct kvm *kvm)
 {
 	spin_lock_init(&kvm->irqfds.lock);
 	INIT_LIST_HEAD(&kvm->irqfds.items);
+	INIT_LIST_HEAD(&kvm->irqfds.oadns);
 	INIT_LIST_HEAD(&kvm->ioeventfds);
 }
 
@@ -340,7 +527,7 @@ kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
 int
 kvm_irqfd(struct kvm *kvm, struct kvm_irqfd *args)
 {
-	if (args->flags & ~KVM_IRQFD_FLAG_DEASSIGN)
+	if (args->flags & ~(KVM_IRQFD_FLAG_DEASSIGN | KVM_IRQFD_FLAG_OADN))
 		return -EINVAL;
 
 	if (args->flags & KVM_IRQFD_FLAG_DEASSIGN)

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