[PATCH v7 2/2] kvm: KVM_EOIFD, an eventfd for EOIs

From: Alex Williamson
Date: Tue Jul 24 2012 - 16:43:21 EST

This new ioctl enables an eventfd to be triggered when an EOI is
written for a specified irqchip pin. The first user of this will
be external device assignment through VFIO, using a level irqfd
for asserting a PCI INTx interrupt and this interface for de-assert
and notification once the interrupt is serviced.

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@xxxxxxxxxx>
---

Documentation/virtual/kvm/api.txt | 21 ++
arch/x86/kvm/x86.c | 2
include/linux/kvm.h | 15 ++
include/linux/kvm_host.h | 13 +
virt/kvm/eventfd.c | 336 +++++++++++++++++++++++++++++++++++++
virt/kvm/kvm_main.c | 11 +
6 files changed, 398 insertions(+)

diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt
index 3911e62..8cd6b36 100644
--- a/Documentation/virtual/kvm/api.txt
+++ b/Documentation/virtual/kvm/api.txt
@@ -1989,6 +1989,27 @@ return the hash table order in the parameter. (If the guest is using
the virtualized real-mode area (VRMA) facility, the kernel will
re-create the VMRA HPTEs on the next KVM_RUN of any vcpu.)

+4.77 KVM_EOIFD
+
+Capability: KVM_CAP_EOIFD
+Architectures: x86
+Type: vm ioctl
+Parameters: struct kvm_eoifd (in)
+Returns: 0 on success, < 0 on error
+
+KVM_EOIFD allows userspace to receive interrupt EOI notification
+through an eventfd. kvm_eoifd.fd specifies the eventfd used for
+notification. KVM_EOIFD_FLAG_DEASSIGN is used to de-assign an eoifd
+once assigned. KVM_EOIFD also requires additional bits set in
+kvm_eoifd.flags to bind to the proper interrupt line. The
+KVM_EOIFD_FLAG_LEVEL_IRQFD indicates that kvm_eoifd.key is provided
+and is a key from a level triggered interrupt (configured from
+KVM_IRQFD using KVM_IRQFD_FLAG_LEVEL). The EOI notification is bound
+to the same GSI and irqchip input as the irqfd. Both kvm_eoifd.key
+and KVM_EOIFD_FLAG_LEVEL_IRQFD must be specified on assignment and
+de-assignment of KVM_EOIFD. A level irqfd may only be bound to a
+single eoifd. KVM_CAP_EOIFD_LEVEL_IRQFD indicates support of
+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 9ded39d..8f3164e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2171,6 +2171,8 @@ 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:
+ case KVM_CAP_EOIFD_LEVEL_IRQFD:
r = 1;
break;
case KVM_CAP_COALESCED_MMIO:
diff --git a/include/linux/kvm.h b/include/linux/kvm.h
index b2e6e4f..effb916 100644
--- a/include/linux/kvm.h
+++ b/include/linux/kvm.h
@@ -619,6 +619,8 @@ 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
+#define KVM_CAP_EOIFD_LEVEL_IRQFD 83

#ifdef KVM_CAP_IRQ_ROUTING

@@ -694,6 +696,17 @@ struct kvm_irqfd {
__u8 pad[20];
};

+#define KVM_EOIFD_FLAG_DEASSIGN (1 << 0)
+/* Available with KVM_CAP_EOIFD_LEVEL_IRQFD */
+#define KVM_EOIFD_FLAG_LEVEL_IRQFD (1 << 1)
+
+struct kvm_eoifd {
+ __u32 fd;
+ __u32 flags;
+ __u32 key;
+ __u8 pad[20];
+};
+
struct kvm_clock_data {
__u64 clock;
__u32 flags;
@@ -834,6 +847,8 @@ 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 c73f071..01e72a6 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -289,6 +289,10 @@ struct kvm {
struct mutex lock;
struct list_head items;
} irqsources;
+ struct {
+ spinlock_t lock;
+ struct list_head items;
+ } eoifds;
#endif
struct kvm_vm_stat stat;
struct kvm_arch arch;
@@ -832,6 +836,8 @@ 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

@@ -857,6 +863,13 @@ 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 878cb52..3aa2d62 100644
--- a/virt/kvm/eventfd.c
+++ b/virt/kvm/eventfd.c
@@ -95,6 +95,25 @@ static struct _irq_source *_irq_source_alloc(struct kvm *kvm, int gsi)
return source;
}

+static struct _irq_source *_irq_source_get_from_key(struct kvm *kvm, int key)
+{
+ struct _irq_source *tmp, *source = ERR_PTR(-ENOENT);
+
+ mutex_lock(&kvm->irqsources.lock);
+
+ list_for_each_entry(tmp, &kvm->irqsources.items, list) {
+ if (tmp->id == key) {
+ source = tmp;
+ kref_get(&source->kref);
+ break;
+ }
+ }
+
+ mutex_unlock(&kvm->irqsources.lock);
+
+ return source;
+}
+
/*
* --------------------------------------------------------------------
* irqfd: Allows an fd to be used to inject an interrupt to the guest
@@ -406,6 +425,8 @@ kvm_eventfd_init(struct kvm *kvm)
INIT_LIST_HEAD(&kvm->ioeventfds);
mutex_init(&kvm->irqsources.lock);
INIT_LIST_HEAD(&kvm->irqsources.items);
+ spin_lock_init(&kvm->eoifds.lock);
+ INIT_LIST_HEAD(&kvm->eoifds.items);
}

/*
@@ -772,3 +793,318 @@ 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 with an eventfd for receiving
+ * notification when an EOI occurs.
+ * --------------------------------------------------------------------
+ */
+
+struct _eoifd {
+ /* eventfd triggered on EOI */
+ struct eventfd_ctx *eventfd;
+ /* irq source ID de-asserted on EOI */
+ struct _irq_source *source;
+ wait_queue_t wait;
+ /* EOI notification from KVM */
+ struct kvm_irq_ack_notifier notifier;
+ struct list_head list;
+ poll_table pt;
+ struct work_struct shutdown;
+};
+
+/* Called under eoifds.lock */
+static void eoifd_shutdown(struct work_struct *work)
+{
+ struct _eoifd *eoifd = container_of(work, struct _eoifd, shutdown);
+ struct kvm *kvm = eoifd->source->kvm;
+ u64 cnt;
+
+ /*
+ * Stop EOI signaling
+ */
+ kvm_unregister_irq_ack_notifier(kvm, &eoifd->notifier);
+
+ /*
+ * Synchronize with the wait-queue and unhook ourselves to prevent
+ * further events.
+ */
+ eventfd_ctx_remove_wait_queue(eoifd->eventfd, &eoifd->wait, &cnt);
+
+ /*
+ * Release resources
+ */
+ eventfd_ctx_put(eoifd->eventfd);
+ _irq_source_put(eoifd->source);
+ kfree(eoifd);
+}
+
+/* assumes kvm->eoifds.lock is held */
+static bool eoifd_is_active(struct _eoifd *eoifd)
+{
+ return list_empty(&eoifd->list) ? false : true;
+}
+
+/*
+ * Mark the eoifd as inactive and schedule it for removal
+ *
+ * assumes kvm->eoifds.lock is held
+ */
+static void eoifd_deactivate(struct _eoifd *eoifd)
+{
+ BUG_ON(!eoifd_is_active(eoifd));
+
+ list_del_init(&eoifd->list);
+
+ queue_work(irqfd_cleanup_wq, &eoifd->shutdown);
+}
+
+/*
+ * Called with wqh->lock held and interrupts disabled
+ */
+static int eoifd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+ unsigned long flags = (unsigned long)key;
+
+ if (unlikely(flags & POLLHUP)) {
+ /* The eventfd is closing, detach from KVM */
+ struct _eoifd *eoifd = container_of(wait, struct _eoifd, wait);
+ struct kvm *kvm = eoifd->source->kvm;
+ unsigned long flags;
+
+ spin_lock_irqsave(&kvm->eoifds.lock, flags);
+
+ /*
+ * We must check if someone deactivated the eoifd before
+ * we could acquire the eoifds.lock since the item is
+ * deactivated from the KVM side before it is unhooked from
+ * the wait-queue. If it is already deactivated, we can
+ * simply return knowing the other side will cleanup for us.
+ * We cannot race against the eoifd going away since the
+ * other side is required to acquire wqh->lock, which we hold
+ */
+ if (eoifd_is_active(eoifd))
+ eoifd_deactivate(eoifd);
+
+ spin_unlock_irqrestore(&kvm->eoifds.lock, flags);
+ }
+
+ return 0;
+}
+
+static void eoifd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
+ poll_table *pt)
+{
+ struct _eoifd *eoifd = container_of(pt, struct _eoifd, pt);
+ add_wait_queue(wqh, &eoifd->wait);
+}
+
+/*
+ * This function is called as the kvm VM fd is being released. Shutdown all
+ * eoifds that still remain open
+ */
+void kvm_eoifd_release(struct kvm *kvm)
+{
+ struct _eoifd *tmp, *eoifd;
+
+ spin_lock_irq(&kvm->eoifds.lock);
+
+ list_for_each_entry_safe(eoifd, tmp, &kvm->eoifds.items, list)
+ eoifd_deactivate(eoifd);
+
+ spin_unlock_irq(&kvm->eoifds.lock);
+
+ flush_workqueue(irqfd_cleanup_wq);
+}
+
+static void eoifd_event(struct kvm_irq_ack_notifier *notifier)
+{
+ struct _eoifd *eoifd;
+
+ eoifd = container_of(notifier, struct _eoifd, notifier);
+
+ if (unlikely(!eoifd->source))
+ return;
+
+ /*
+ * De-assert and send EOI, user needs to re-assert if
+ * device still requires service.
+ */
+ kvm_set_irq(eoifd->source->kvm,
+ eoifd->source->id, eoifd->source->gsi, 0);
+ eventfd_signal(eoifd->eventfd, 1);
+}
+
+static int kvm_assign_eoifd(struct kvm *kvm, struct kvm_eoifd *args)
+{
+ struct file *file = NULL;
+ struct eventfd_ctx *eventfd = NULL;
+ struct _eoifd *eoifd = NULL, *tmp;
+ struct _irq_source *source = NULL;
+ int ret;
+ u64 cnt;
+
+ if (!(args->flags & KVM_EOIFD_FLAG_LEVEL_IRQFD))
+ return -EINVAL;
+
+ file = eventfd_fget(args->fd);
+ if (IS_ERR(file)) {
+ ret = PTR_ERR(file);
+ goto fail;
+ }
+
+ eventfd = eventfd_ctx_fileget(file);
+ if (IS_ERR(eventfd)) {
+ ret = PTR_ERR(eventfd);
+ goto fail;
+ }
+
+ eoifd = kzalloc(sizeof(*eoifd), GFP_KERNEL);
+ if (!eoifd) {
+ ret = -ENOMEM;
+ goto fail;
+ }
+
+ source = _irq_source_get_from_key(kvm, args->key);
+ if (IS_ERR(source)) {
+ ret = PTR_ERR(source);
+ goto fail;
+ }
+
+ INIT_LIST_HEAD(&eoifd->list);
+ INIT_WORK(&eoifd->shutdown, eoifd_shutdown);
+ eoifd->eventfd = eventfd;
+ eoifd->notifier.gsi = source->gsi;
+ eoifd->notifier.irq_acked = eoifd_event;
+
+ /*
+ * Install our own custom wake-up handling so we are notified via
+ * a callback whenever someone releases the underlying eventfd
+ */
+ init_waitqueue_func_entry(&eoifd->wait, eoifd_wakeup);
+ init_poll_funcptr(&eoifd->pt, eoifd_ptable_queue_proc);
+
+ /*
+ * Clear out any previously released eoifds that might conflict
+ */
+ flush_workqueue(irqfd_cleanup_wq);
+
+ /*
+ * This can sleep, so register before acquiring spinlock, notifier
+ * becomes a nop until we finish.
+ */
+ kvm_register_irq_ack_notifier(kvm, &eoifd->notifier);
+
+ /*
+ * Install the wait queue function to allow cleanup when the
+ * eventfd is closed by the user. This grabs the wqh lock, so
+ * we do it out of spinlock, holding the file reference ensures
+ * we won't see a POLLHUP until setup is complete.
+ */
+ file->f_op->poll(file, &eoifd->pt);
+
+ spin_lock_irq(&kvm->eoifds.lock);
+
+ /*
+ * Enforce a one-to-one relationship between irq source and eoifd so
+ * that this interface can't be used to consume all kernel memory.
+ * NB. single eventfd can still be used by multiple eoifds.
+ */
+ list_for_each_entry(tmp, &kvm->eoifds.items, list) {
+ if (tmp->source == source) {
+ spin_unlock_irq(&kvm->eoifds.lock);
+ ret = -EBUSY;
+ goto fail_unregister;
+ }
+ }
+
+ list_add_tail(&eoifd->list, &kvm->eoifds.items);
+ eoifd->source = source; /* Enable ack notifier */
+
+ spin_unlock_irq(&kvm->eoifds.lock);
+
+ fput(file); /* Enable POLLHUP */
+
+ return 0;
+
+fail_unregister:
+ eventfd_ctx_remove_wait_queue(eventfd, &eoifd->wait, &cnt);
+ kvm_unregister_irq_ack_notifier(kvm, &eoifd->notifier);
+fail:
+ if (source && !IS_ERR(source))
+ _irq_source_put(source);
+
+ if (eventfd && !IS_ERR(eventfd))
+ eventfd_ctx_put(eventfd);
+
+ if (file && !IS_ERR(file))
+ fput(file);
+
+ kfree(eoifd);
+ return ret;
+}
+
+static int kvm_deassign_eoifd(struct kvm *kvm, struct kvm_eoifd *args)
+{
+ struct eventfd_ctx *eventfd = NULL;
+ struct _irq_source *source = NULL;
+ struct _eoifd *eoifd;
+ int ret = -ENOENT;
+
+ if (!(args->flags & KVM_EOIFD_FLAG_LEVEL_IRQFD))
+ return -EINVAL;
+
+ eventfd = eventfd_ctx_fdget(args->fd);
+ if (IS_ERR(eventfd)) {
+ ret = PTR_ERR(eventfd);
+ goto fail;
+ }
+
+ source = _irq_source_get_from_key(kvm, args->key);
+ if (IS_ERR(source)) {
+ ret = PTR_ERR(source);
+ goto fail;
+ }
+
+ spin_lock_irq(&kvm->eoifds.lock);
+
+ list_for_each_entry(eoifd, &kvm->eoifds.items, list) {
+ if (eoifd->eventfd == eventfd && eoifd->source == source) {
+ eoifd_deactivate(eoifd);
+ ret = 0;
+ break;
+ }
+ }
+
+ spin_unlock_irq(&kvm->eoifds.lock);
+
+fail:
+ if (source && !IS_ERR(source))
+ _irq_source_put(source);
+ if (eventfd && !IS_ERR(eventfd))
+ eventfd_ctx_put(eventfd);
+
+ /*
+ * Block until we know all outstanding shutdown jobs have completed
+ * so that we guarantee there will not be any more EOIs signaled on
+ * this eventfd once this deassign function returns.
+ */
+ flush_workqueue(irqfd_cleanup_wq);
+
+ 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 2468523..0b241bf 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)

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