KVM: irqfd

KVM provides a complete virtual system environment for guests, including
support for injecting interrupts modeled after the real exception/interrupt
facilities present on the native platform (such as the IDT on x86).
Virtual interrupts can come from a variety of sources (emulated devices,
pass-through devices, etc) but all must be injected to the guest via
the KVM infrastructure.  This patch adds a new mechanism to inject a specific
interrupt to a guest using a decoupled eventfd mechnanism:  Any legal signal
on the irqfd (using eventfd semantics from either userspace or kernel) will
translate into an injected interrupt in the guest at the next available
interrupt window.

Signed-off-by: Gregory Haskins <ghaskins@novell.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 329 insertions, 0 deletions

diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
new file mode 100644
index 000000000000..314012323afe
--- /dev/null
+++ b/virt/kvm/eventfd.c
@@ -0,0 +1,329 @@
+/*
+ * kvm eventfd support - use eventfd objects to signal various KVM events
+ *
+ * Copyright 2009 Novell.  All Rights Reserved.
+ *
+ * Author:
+ *      Gregory Haskins <ghaskins@novell.com>
+ *
+ * This file is free software; you can redistribute it and/or modify
+ * it under the terms of version 2 of the GNU General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
+ */
+
+#include <linux/kvm_host.h>
+#include <linux/workqueue.h>
+#include <linux/syscalls.h>
+#include <linux/wait.h>
+#include <linux/poll.h>
+#include <linux/file.h>
+#include <linux/list.h>
+#include <linux/eventfd.h>
+
+/*
+ * --------------------------------------------------------------------
+ * irqfd: Allows an fd to be used to inject an interrupt to the guest
+ *
+ * Credit goes to Avi Kivity for the original idea.
+ * --------------------------------------------------------------------
+ */
+
+struct _irqfd {
+        struct kvm               *kvm;
+        struct eventfd_ctx       *eventfd;
+        int                       gsi;
+        struct list_head          list;
+        poll_table                pt;
+        wait_queue_head_t        *wqh;
+        wait_queue_t              wait;
+        struct work_struct        inject;
+        struct work_struct        shutdown;
+};
+
+static struct workqueue_struct *irqfd_cleanup_wq;
+
+static void
+irqfd_inject(struct work_struct *work)
+{
+        struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
+        struct kvm *kvm = irqfd->kvm;
+
+        mutex_lock(&kvm->lock);
+        kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
+        kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
+        mutex_unlock(&kvm->lock);
+}
+
+/*
+ * Race-free decouple logic (ordering is critical)
+ */
+static void
+irqfd_shutdown(struct work_struct *work)
+{
+        struct _irqfd *irqfd = container_of(work, struct _irqfd, shutdown);
+
+        /*
+         * Synchronize with the wait-queue and unhook ourselves to prevent
+         * further events.
+         */
+        remove_wait_queue(irqfd->wqh, &irqfd->wait);
+
+        /*
+         * We know no new events will be scheduled at this point, so block
+         * until all previously outstanding events have completed
+         */
+        flush_work(&irqfd->inject);
+
+        /*
+         * It is now safe to release the object's resources
+         */
+        eventfd_ctx_put(irqfd->eventfd);
+        kfree(irqfd);
+}
+
+
+/* assumes kvm->irqfds.lock is held */
+static bool
+irqfd_is_active(struct _irqfd *irqfd)
+{
+        return list_empty(&irqfd->list) ? false : true;
+}
+
+/*
+ * Mark the irqfd as inactive and schedule it for removal
+ *
+ * assumes kvm->irqfds.lock is held
+ */
+static void
+irqfd_deactivate(struct _irqfd *irqfd)
+{
+        BUG_ON(!irqfd_is_active(irqfd));
+
+        list_del_init(&irqfd->list);
+
+        queue_work(irqfd_cleanup_wq, &irqfd->shutdown);
+}
+
+/*
+ * Called with wqh->lock held and interrupts disabled
+ */
+static int
+irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
+{
+        struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
+        unsigned long flags = (unsigned long)key;
+
+        if (flags & POLLIN)
+                /* An event has been signaled, inject an interrupt */
+                schedule_work(&irqfd->inject);
+
+        if (flags & POLLHUP) {
+                /* The eventfd is closing, detach from KVM */
+                struct kvm *kvm = irqfd->kvm;
+                unsigned long flags;
+
+                spin_lock_irqsave(&kvm->irqfds.lock, flags);
+
+                /*
+                 * We must check if someone deactivated the irqfd before
+                 * we could acquire the irqfds.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 irqfd going away since the
+                 * other side is required to acquire wqh->lock, which we hold
+                 */
+                if (irqfd_is_active(irqfd))
+                        irqfd_deactivate(irqfd);
+
+                spin_unlock_irqrestore(&kvm->irqfds.lock, flags);
+        }
+
+        return 0;
+}
+
+static void
+irqfd_ptable_queue_proc(struct file *file, wait_queue_head_t *wqh,
+                        poll_table *pt)
+{
+        struct _irqfd *irqfd = container_of(pt, struct _irqfd, pt);
+
+        irqfd->wqh = wqh;
+        add_wait_queue(wqh, &irqfd->wait);
+}
+
+static int
+kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
+{
+        struct _irqfd *irqfd;
+        struct file *file = NULL;
+        struct eventfd_ctx *eventfd = NULL;
+        int ret;
+        unsigned int events;
+
+        irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
+        if (!irqfd)
+                return -ENOMEM;
+
+        irqfd->kvm = kvm;
+        irqfd->gsi = gsi;
+        INIT_LIST_HEAD(&irqfd->list);
+        INIT_WORK(&irqfd->inject, irqfd_inject);
+        INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
+
+        file = eventfd_fget(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;
+        }
+
+        irqfd->eventfd = eventfd;
+
+        /*
+         * Install our own custom wake-up handling so we are notified via
+         * a callback whenever someone signals the underlying eventfd
+         */
+        init_waitqueue_func_entry(&irqfd->wait, irqfd_wakeup);
+        init_poll_funcptr(&irqfd->pt, irqfd_ptable_queue_proc);
+
+        events = file->f_op->poll(file, &irqfd->pt);
+
+        spin_lock_irq(&kvm->irqfds.lock);
+        list_add_tail(&irqfd->list, &kvm->irqfds.items);
+        spin_unlock_irq(&kvm->irqfds.lock);
+
+        /*
+         * Check if there was an event already pending on the eventfd
+         * before we registered, and trigger it as if we didn't miss it.
+         */
+        if (events & POLLIN)
+                schedule_work(&irqfd->inject);
+
+        /*
+         * do not drop the file until the irqfd is fully initialized, otherwise
+         * we might race against the POLLHUP
+         */
+        fput(file);
+
+        return 0;
+
+fail:
+        if (eventfd && !IS_ERR(eventfd))
+                eventfd_ctx_put(eventfd);
+
+        if (file && !IS_ERR(file))
+                fput(file);
+
+        kfree(irqfd);
+        return ret;
+}
+
+void
+kvm_irqfd_init(struct kvm *kvm)
+{
+        spin_lock_init(&kvm->irqfds.lock);
+        INIT_LIST_HEAD(&kvm->irqfds.items);
+}
+
+/*
+ * shutdown any irqfd's that match fd+gsi
+ */
+static int
+kvm_irqfd_deassign(struct kvm *kvm, int fd, int gsi)
+{
+        struct _irqfd *irqfd, *tmp;
+        struct eventfd_ctx *eventfd;
+
+        eventfd = eventfd_ctx_fdget(fd);
+        if (IS_ERR(eventfd))
+                return PTR_ERR(eventfd);
+
+        spin_lock_irq(&kvm->irqfds.lock);
+
+        list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list) {
+                if (irqfd->eventfd == eventfd && irqfd->gsi == gsi)
+                        irqfd_deactivate(irqfd);
+        }
+
+        spin_unlock_irq(&kvm->irqfds.lock);
+        eventfd_ctx_put(eventfd);
+
+        /*
+         * Block until we know all outstanding shutdown jobs have completed
+         * so that we guarantee there will not be any more interrupts on this
+         * gsi once this deassign function returns.
+         */
+        flush_workqueue(irqfd_cleanup_wq);
+
+        return 0;
+}
+
+int
+kvm_irqfd(struct kvm *kvm, int fd, int gsi, int flags)
+{
+        if (flags & KVM_IRQFD_FLAG_DEASSIGN)
+                return kvm_irqfd_deassign(kvm, fd, gsi);
+
+        return kvm_irqfd_assign(kvm, fd, gsi);
+}
+
+/*
+ * This function is called as the kvm VM fd is being released. Shutdown all
+ * irqfds that still remain open
+ */
+void
+kvm_irqfd_release(struct kvm *kvm)
+{
+        struct _irqfd *irqfd, *tmp;
+
+        spin_lock_irq(&kvm->irqfds.lock);
+
+        list_for_each_entry_safe(irqfd, tmp, &kvm->irqfds.items, list)
+                irqfd_deactivate(irqfd);
+
+        spin_unlock_irq(&kvm->irqfds.lock);
+
+        /*
+         * Block until we know all outstanding shutdown jobs have completed
+         * since we do not take a kvm* reference.
+         */
+        flush_workqueue(irqfd_cleanup_wq);
+
+}
+
+/*
+ * create a host-wide workqueue for issuing deferred shutdown requests
+ * aggregated from all vm* instances. We need our own isolated single-thread
+ * queue to prevent deadlock against flushing the normal work-queue.
+ */
+static int __init irqfd_module_init(void)
+{
+        irqfd_cleanup_wq = create_singlethread_workqueue("kvm-irqfd-cleanup");
+        if (!irqfd_cleanup_wq)
+                return -ENOMEM;
+
+        return 0;
+}
+
+static void __exit irqfd_module_exit(void)
+{
+        destroy_workqueue(irqfd_cleanup_wq);
+}
+
+module_init(irqfd_module_init);
+module_exit(irqfd_module_exit);