Linux 4.1.18

[linux/fpc-iii.git] / virt / kvm / eventfd.c

/*
 * kvm eventfd support - use eventfd objects to signal various KVM events
 *
 * Copyright 2009 Novell.  All Rights Reserved.
 * Copyright 2010 Red Hat, Inc. and/or its affiliates.
 *
 * 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/kvm.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>
#include <linux/kernel.h>
#include <linux/srcu.h>
#include <linux/slab.h>
#include <linux/seqlock.h>
#include <trace/events/kvm.h>

#include <kvm/iodev.h>

#ifdef CONFIG_HAVE_KVM_IRQFD
/*
 * --------------------------------------------------------------------
 * irqfd: Allows an fd to be used to inject an interrupt to the guest
 *
 * Credit goes to Avi Kivity for the original idea.
 * --------------------------------------------------------------------
 */

/*
 * Resampling irqfds are a special variety of irqfds used to emulate
 * level triggered interrupts.  The interrupt is asserted on eventfd
 * trigger.  On acknowledgement through the irq ack notifier, the
 * interrupt is de-asserted and userspace is notified through the
 * resamplefd.  All resamplers on the same gsi are de-asserted
 * together, so we don't need to track the state of each individual
 * user.  We can also therefore share the same irq source ID.
 */
struct _irqfd_resampler {
        struct kvm *kvm;
        /*
         * List of resampling struct _irqfd objects sharing this gsi.
         * RCU list modified under kvm->irqfds.resampler_lock
         */
        struct list_head list;
        struct kvm_irq_ack_notifier notifier;
        /*
         * Entry in list of kvm->irqfd.resampler_list.  Use for sharing
         * resamplers among irqfds on the same gsi.
         * Accessed and modified under kvm->irqfds.resampler_lock
         */
        struct list_head link;
};

struct _irqfd {
        /* Used for MSI fast-path */
        struct kvm *kvm;
        wait_queue_t wait;
        /* Update side is protected by irqfds.lock */
        struct kvm_kernel_irq_routing_entry irq_entry;
        seqcount_t irq_entry_sc;
        /* Used for level IRQ fast-path */
        int gsi;
        struct work_struct inject;
        /* The resampler used by this irqfd (resampler-only) */
        struct _irqfd_resampler *resampler;
        /* Eventfd notified on resample (resampler-only) */
        struct eventfd_ctx *resamplefd;
        /* Entry in list of irqfds for a resampler (resampler-only) */
        struct list_head resampler_link;
        /* Used for setup/shutdown */
        struct eventfd_ctx *eventfd;
        struct list_head list;
        poll_table pt;
        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;

        if (!irqfd->resampler) {
                kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1,
                                false);
                kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0,
                                false);
        } else
                kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,
                            irqfd->gsi, 1, false);
}

/*
 * Since resampler irqfds share an IRQ source ID, we de-assert once
 * then notify all of the resampler irqfds using this GSI.  We can't
 * do multiple de-asserts or we risk racing with incoming re-asserts.
 */
static void
irqfd_resampler_ack(struct kvm_irq_ack_notifier *kian)
{
        struct _irqfd_resampler *resampler;
        struct kvm *kvm;
        struct _irqfd *irqfd;
        int idx;

        resampler = container_of(kian, struct _irqfd_resampler, notifier);
        kvm = resampler->kvm;

        kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,
                    resampler->notifier.gsi, 0, false);

        idx = srcu_read_lock(&kvm->irq_srcu);

        list_for_each_entry_rcu(irqfd, &resampler->list, resampler_link)
                eventfd_signal(irqfd->resamplefd, 1);

        srcu_read_unlock(&kvm->irq_srcu, idx);
}

static void
irqfd_resampler_shutdown(struct _irqfd *irqfd)
{
        struct _irqfd_resampler *resampler = irqfd->resampler;
        struct kvm *kvm = resampler->kvm;

        mutex_lock(&kvm->irqfds.resampler_lock);

        list_del_rcu(&irqfd->resampler_link);
        synchronize_srcu(&kvm->irq_srcu);

        if (list_empty(&resampler->list)) {
                list_del(&resampler->link);
                kvm_unregister_irq_ack_notifier(kvm, &resampler->notifier);
                kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,
                            resampler->notifier.gsi, 0, false);
                kfree(resampler);
        }

        mutex_unlock(&kvm->irqfds.resampler_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);
        u64 cnt;

        /*
         * Synchronize with the wait-queue and unhook ourselves to prevent
         * further events.
         */
        eventfd_ctx_remove_wait_queue(irqfd->eventfd, &irqfd->wait, &cnt);

        /*
         * We know no new events will be scheduled at this point, so block
         * until all previously outstanding events have completed
         */
        flush_work(&irqfd->inject);

        if (irqfd->resampler) {
                irqfd_resampler_shutdown(irqfd);
                eventfd_ctx_put(irqfd->resamplefd);
        }

        /*
         * 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;
        struct kvm_kernel_irq_routing_entry irq;
        struct kvm *kvm = irqfd->kvm;
        unsigned seq;
        int idx;

        if (flags & POLLIN) {
                idx = srcu_read_lock(&kvm->irq_srcu);
                do {
                        seq = read_seqcount_begin(&irqfd->irq_entry_sc);
                        irq = irqfd->irq_entry;
                } while (read_seqcount_retry(&irqfd->irq_entry_sc, seq));
                /* An event has been signaled, inject an interrupt */
                if (irq.type == KVM_IRQ_ROUTING_MSI)
                        kvm_set_msi(&irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1,
                                        false);
                else
                        schedule_work(&irqfd->inject);
                srcu_read_unlock(&kvm->irq_srcu, idx);
        }

        if (flags & POLLHUP) {
                /* The eventfd is closing, detach from 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);
        add_wait_queue(wqh, &irqfd->wait);
}

/* Must be called under irqfds.lock */
static void irqfd_update(struct kvm *kvm, struct _irqfd *irqfd)
{
        struct kvm_kernel_irq_routing_entry *e;
        struct kvm_kernel_irq_routing_entry entries[KVM_NR_IRQCHIPS];
        int i, n_entries;

        n_entries = kvm_irq_map_gsi(kvm, entries, irqfd->gsi);

        write_seqcount_begin(&irqfd->irq_entry_sc);

        irqfd->irq_entry.type = 0;

        e = entries;
        for (i = 0; i < n_entries; ++i, ++e) {
                /* Only fast-path MSI. */
                if (e->type == KVM_IRQ_ROUTING_MSI)
                        irqfd->irq_entry = *e;
        }

        write_seqcount_end(&irqfd->irq_entry_sc);
}

static int
kvm_irqfd_assign(struct kvm *kvm, struct kvm_irqfd *args)
{
        struct _irqfd *irqfd, *tmp;
        struct fd f;
        struct eventfd_ctx *eventfd = NULL, *resamplefd = NULL;
        int ret;
        unsigned int events;
        int idx;

        if (!kvm_arch_intc_initialized(kvm))
                return -EAGAIN;

        irqfd = kzalloc(sizeof(*irqfd), GFP_KERNEL);
        if (!irqfd)
                return -ENOMEM;

        irqfd->kvm = kvm;
        irqfd->gsi = args->gsi;
        INIT_LIST_HEAD(&irqfd->list);
        INIT_WORK(&irqfd->inject, irqfd_inject);
        INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
        seqcount_init(&irqfd->irq_entry_sc);

        f = fdget(args->fd);
        if (!f.file) {
                ret = -EBADF;
                goto out;
        }

        eventfd = eventfd_ctx_fileget(f.file);
        if (IS_ERR(eventfd)) {
                ret = PTR_ERR(eventfd);
                goto fail;
        }

        irqfd->eventfd = eventfd;

        if (args->flags & KVM_IRQFD_FLAG_RESAMPLE) {
                struct _irqfd_resampler *resampler;

                resamplefd = eventfd_ctx_fdget(args->resamplefd);
                if (IS_ERR(resamplefd)) {
                        ret = PTR_ERR(resamplefd);
                        goto fail;
                }

                irqfd->resamplefd = resamplefd;
                INIT_LIST_HEAD(&irqfd->resampler_link);

                mutex_lock(&kvm->irqfds.resampler_lock);

                list_for_each_entry(resampler,
                                    &kvm->irqfds.resampler_list, link) {
                        if (resampler->notifier.gsi == irqfd->gsi) {
                                irqfd->resampler = resampler;
                                break;
                        }
                }

                if (!irqfd->resampler) {
                        resampler = kzalloc(sizeof(*resampler), GFP_KERNEL);
                        if (!resampler) {
                                ret = -ENOMEM;
                                mutex_unlock(&kvm->irqfds.resampler_lock);
                                goto fail;
                        }

                        resampler->kvm = kvm;
                        INIT_LIST_HEAD(&resampler->list);
                        resampler->notifier.gsi = irqfd->gsi;
                        resampler->notifier.irq_acked = irqfd_resampler_ack;
                        INIT_LIST_HEAD(&resampler->link);

                        list_add(&resampler->link, &kvm->irqfds.resampler_list);
                        kvm_register_irq_ack_notifier(kvm,
                                                      &resampler->notifier);
                        irqfd->resampler = resampler;
                }

                list_add_rcu(&irqfd->resampler_link, &irqfd->resampler->list);
                synchronize_srcu(&kvm->irq_srcu);

                mutex_unlock(&kvm->irqfds.resampler_lock);
        }

        /*
         * 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);

        spin_lock_irq(&kvm->irqfds.lock);

        ret = 0;
        list_for_each_entry(tmp, &kvm->irqfds.items, list) {
                if (irqfd->eventfd != tmp->eventfd)
                        continue;
                /* This fd is used for another irq already. */
                ret = -EBUSY;
                spin_unlock_irq(&kvm->irqfds.lock);
                goto fail;
        }

        idx = srcu_read_lock(&kvm->irq_srcu);
        irqfd_update(kvm, irqfd);
        srcu_read_unlock(&kvm->irq_srcu, idx);

        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.
         */
        events = f.file->f_op->poll(f.file, &irqfd->pt);

        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
         */
        fdput(f);

        return 0;

fail:
        if (irqfd->resampler)
                irqfd_resampler_shutdown(irqfd);

        if (resamplefd && !IS_ERR(resamplefd))
                eventfd_ctx_put(resamplefd);

        if (eventfd && !IS_ERR(eventfd))
                eventfd_ctx_put(eventfd);

        fdput(f);

out:
        kfree(irqfd);
        return ret;
}

bool kvm_irq_has_notifier(struct kvm *kvm, unsigned irqchip, unsigned pin)
{
        struct kvm_irq_ack_notifier *kian;
        int gsi, idx;

        idx = srcu_read_lock(&kvm->irq_srcu);
        gsi = kvm_irq_map_chip_pin(kvm, irqchip, pin);
        if (gsi != -1)
                hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list,
                                         link)
                        if (kian->gsi == gsi) {
                                srcu_read_unlock(&kvm->irq_srcu, idx);
                                return true;
                        }

        srcu_read_unlock(&kvm->irq_srcu, idx);

        return false;
}
EXPORT_SYMBOL_GPL(kvm_irq_has_notifier);

void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
{
        struct kvm_irq_ack_notifier *kian;
        int gsi, idx;

        trace_kvm_ack_irq(irqchip, pin);

        idx = srcu_read_lock(&kvm->irq_srcu);
        gsi = kvm_irq_map_chip_pin(kvm, irqchip, pin);
        if (gsi != -1)
                hlist_for_each_entry_rcu(kian, &kvm->irq_ack_notifier_list,
                                         link)
                        if (kian->gsi == gsi)
                                kian->irq_acked(kian);
        srcu_read_unlock(&kvm->irq_srcu, idx);
}

void kvm_register_irq_ack_notifier(struct kvm *kvm,
                                   struct kvm_irq_ack_notifier *kian)
{
        mutex_lock(&kvm->irq_lock);
        hlist_add_head_rcu(&kian->link, &kvm->irq_ack_notifier_list);
        mutex_unlock(&kvm->irq_lock);
        kvm_vcpu_request_scan_ioapic(kvm);
}

void kvm_unregister_irq_ack_notifier(struct kvm *kvm,
                                    struct kvm_irq_ack_notifier *kian)
{
        mutex_lock(&kvm->irq_lock);
        hlist_del_init_rcu(&kian->link);
        mutex_unlock(&kvm->irq_lock);
        synchronize_srcu(&kvm->irq_srcu);
        kvm_vcpu_request_scan_ioapic(kvm);
}
#endif

void
kvm_eventfd_init(struct kvm *kvm)
{
#ifdef CONFIG_HAVE_KVM_IRQFD
        spin_lock_init(&kvm->irqfds.lock);
        INIT_LIST_HEAD(&kvm->irqfds.items);
        INIT_LIST_HEAD(&kvm->irqfds.resampler_list);
        mutex_init(&kvm->irqfds.resampler_lock);
#endif
        INIT_LIST_HEAD(&kvm->ioeventfds);
}

#ifdef CONFIG_HAVE_KVM_IRQFD
/*
 * shutdown any irqfd's that match fd+gsi
 */
static int
kvm_irqfd_deassign(struct kvm *kvm, struct kvm_irqfd *args)
{
        struct _irqfd *irqfd, *tmp;
        struct eventfd_ctx *eventfd;

        eventfd = eventfd_ctx_fdget(args->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 == args->gsi) {
                        /*
                         * This clearing of irq_entry.type is needed for when
                         * another thread calls kvm_irq_routing_update before
                         * we flush workqueue below (we synchronize with
                         * kvm_irq_routing_update using irqfds.lock).
                         */
                        write_seqcount_begin(&irqfd->irq_entry_sc);
                        irqfd->irq_entry.type = 0;
                        write_seqcount_end(&irqfd->irq_entry_sc);
                        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, struct kvm_irqfd *args)
{
        if (args->flags & ~(KVM_IRQFD_FLAG_DEASSIGN | KVM_IRQFD_FLAG_RESAMPLE))
                return -EINVAL;

        if (args->flags & KVM_IRQFD_FLAG_DEASSIGN)
                return kvm_irqfd_deassign(kvm, args);

        return kvm_irqfd_assign(kvm, args);
}

/*
 * 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);

}

/*
 * Take note of a change in irq routing.
 * Caller must invoke synchronize_srcu(&kvm->irq_srcu) afterwards.
 */
void kvm_irq_routing_update(struct kvm *kvm)
{
        struct _irqfd *irqfd;

        spin_lock_irq(&kvm->irqfds.lock);

        list_for_each_entry(irqfd, &kvm->irqfds.items, list)
                irqfd_update(kvm, irqfd);

        spin_unlock_irq(&kvm->irqfds.lock);
}

/*
 * 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.
 */
int kvm_irqfd_init(void)
{
        irqfd_cleanup_wq = create_singlethread_workqueue("kvm-irqfd-cleanup");
        if (!irqfd_cleanup_wq)
                return -ENOMEM;

        return 0;
}

void kvm_irqfd_exit(void)
{
        destroy_workqueue(irqfd_cleanup_wq);
}
#endif

/*
 * --------------------------------------------------------------------
 * ioeventfd: translate a PIO/MMIO memory write to an eventfd signal.
 *
 * userspace can register a PIO/MMIO address with an eventfd for receiving
 * notification when the memory has been touched.
 * --------------------------------------------------------------------
 */

struct _ioeventfd {
        struct list_head     list;
        u64                  addr;
        int                  length;
        struct eventfd_ctx  *eventfd;
        u64                  datamatch;
        struct kvm_io_device dev;
        u8                   bus_idx;
        bool                 wildcard;
};

static inline struct _ioeventfd *
to_ioeventfd(struct kvm_io_device *dev)
{
        return container_of(dev, struct _ioeventfd, dev);
}

static void
ioeventfd_release(struct _ioeventfd *p)
{
        eventfd_ctx_put(p->eventfd);
        list_del(&p->list);
        kfree(p);
}

static bool
ioeventfd_in_range(struct _ioeventfd *p, gpa_t addr, int len, const void *val)
{
        u64 _val;

        if (addr != p->addr)
                /* address must be precise for a hit */
                return false;

        if (!p->length)
                /* length = 0 means only look at the address, so always a hit */
                return true;

        if (len != p->length)
                /* address-range must be precise for a hit */
                return false;

        if (p->wildcard)
                /* all else equal, wildcard is always a hit */
                return true;

        /* otherwise, we have to actually compare the data */

        BUG_ON(!IS_ALIGNED((unsigned long)val, len));

        switch (len) {
        case 1:
                _val = *(u8 *)val;
                break;
        case 2:
                _val = *(u16 *)val;
                break;
        case 4:
                _val = *(u32 *)val;
                break;
        case 8:
                _val = *(u64 *)val;
                break;
        default:
                return false;
        }

        return _val == p->datamatch ? true : false;
}

/* MMIO/PIO writes trigger an event if the addr/val match */
static int
ioeventfd_write(struct kvm_vcpu *vcpu, struct kvm_io_device *this, gpa_t addr,
                int len, const void *val)
{
        struct _ioeventfd *p = to_ioeventfd(this);

        if (!ioeventfd_in_range(p, addr, len, val))
                return -EOPNOTSUPP;

        eventfd_signal(p->eventfd, 1);
        return 0;
}

/*
 * This function is called as KVM is completely shutting down.  We do not
 * need to worry about locking just nuke anything we have as quickly as possible
 */
static void
ioeventfd_destructor(struct kvm_io_device *this)
{
        struct _ioeventfd *p = to_ioeventfd(this);

        ioeventfd_release(p);
}

static const struct kvm_io_device_ops ioeventfd_ops = {
        .write      = ioeventfd_write,
        .destructor = ioeventfd_destructor,
};

/* assumes kvm->slots_lock held */
static bool
ioeventfd_check_collision(struct kvm *kvm, struct _ioeventfd *p)
{
        struct _ioeventfd *_p;

        list_for_each_entry(_p, &kvm->ioeventfds, list)
                if (_p->bus_idx == p->bus_idx &&
                    _p->addr == p->addr &&
                    (!_p->length || !p->length ||
                     (_p->length == p->length &&
                      (_p->wildcard || p->wildcard ||
                       _p->datamatch == p->datamatch))))
                        return true;

        return false;
}

static enum kvm_bus ioeventfd_bus_from_flags(__u32 flags)
{
        if (flags & KVM_IOEVENTFD_FLAG_PIO)
                return KVM_PIO_BUS;
        if (flags & KVM_IOEVENTFD_FLAG_VIRTIO_CCW_NOTIFY)
                return KVM_VIRTIO_CCW_NOTIFY_BUS;
        return KVM_MMIO_BUS;
}

static int kvm_assign_ioeventfd_idx(struct kvm *kvm,
                                enum kvm_bus bus_idx,
                                struct kvm_ioeventfd *args)
{

        struct eventfd_ctx *eventfd;
        struct _ioeventfd *p;
        int ret;

        eventfd = eventfd_ctx_fdget(args->fd);
        if (IS_ERR(eventfd))
                return PTR_ERR(eventfd);

        p = kzalloc(sizeof(*p), GFP_KERNEL);
        if (!p) {
                ret = -ENOMEM;
                goto fail;
        }

        INIT_LIST_HEAD(&p->list);
        p->addr    = args->addr;
        p->bus_idx = bus_idx;
        p->length  = args->len;
        p->eventfd = eventfd;

        /* The datamatch feature is optional, otherwise this is a wildcard */
        if (args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH)
                p->datamatch = args->datamatch;
        else
                p->wildcard = true;

        mutex_lock(&kvm->slots_lock);

        /* Verify that there isn't a match already */
        if (ioeventfd_check_collision(kvm, p)) {
                ret = -EEXIST;
                goto unlock_fail;
        }

        kvm_iodevice_init(&p->dev, &ioeventfd_ops);

        ret = kvm_io_bus_register_dev(kvm, bus_idx, p->addr, p->length,
                                      &p->dev);
        if (ret < 0)
                goto unlock_fail;

        kvm->buses[bus_idx]->ioeventfd_count++;
        list_add_tail(&p->list, &kvm->ioeventfds);

        mutex_unlock(&kvm->slots_lock);

        return 0;

unlock_fail:
        mutex_unlock(&kvm->slots_lock);

fail:
        kfree(p);
        eventfd_ctx_put(eventfd);

        return ret;
}

static int
kvm_deassign_ioeventfd_idx(struct kvm *kvm, enum kvm_bus bus_idx,
                           struct kvm_ioeventfd *args)
{
        struct _ioeventfd        *p, *tmp;
        struct eventfd_ctx       *eventfd;
        int                       ret = -ENOENT;

        eventfd = eventfd_ctx_fdget(args->fd);
        if (IS_ERR(eventfd))
                return PTR_ERR(eventfd);

        mutex_lock(&kvm->slots_lock);

        list_for_each_entry_safe(p, tmp, &kvm->ioeventfds, list) {
                bool wildcard = !(args->flags & KVM_IOEVENTFD_FLAG_DATAMATCH);

                if (p->bus_idx != bus_idx ||
                    p->eventfd != eventfd  ||
                    p->addr != args->addr  ||
                    p->length != args->len ||
                    p->wildcard != wildcard)
                        continue;

                if (!p->wildcard && p->datamatch != args->datamatch)
                        continue;

                kvm_io_bus_unregister_dev(kvm, bus_idx, &p->dev);
                kvm->buses[bus_idx]->ioeventfd_count--;
                ioeventfd_release(p);
                ret = 0;
                break;
        }

        mutex_unlock(&kvm->slots_lock);

        eventfd_ctx_put(eventfd);

        return ret;
}

static int kvm_deassign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
        enum kvm_bus bus_idx = ioeventfd_bus_from_flags(args->flags);
        int ret = kvm_deassign_ioeventfd_idx(kvm, bus_idx, args);

        if (!args->len && bus_idx == KVM_MMIO_BUS)
                kvm_deassign_ioeventfd_idx(kvm, KVM_FAST_MMIO_BUS, args);

        return ret;
}

static int
kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
        enum kvm_bus              bus_idx;
        int ret;

        bus_idx = ioeventfd_bus_from_flags(args->flags);
        /* must be natural-word sized, or 0 to ignore length */
        switch (args->len) {
        case 0:
        case 1:
        case 2:
        case 4:
        case 8:
                break;
        default:
                return -EINVAL;
        }

        /* check for range overflow */
        if (args->addr + args->len < args->addr)
                return -EINVAL;

        /* check for extra flags that we don't understand */
        if (args->flags & ~KVM_IOEVENTFD_VALID_FLAG_MASK)
                return -EINVAL;

        /* ioeventfd with no length can't be combined with DATAMATCH */
        if (!args->len &&
            args->flags & (KVM_IOEVENTFD_FLAG_PIO |
                           KVM_IOEVENTFD_FLAG_DATAMATCH))
                return -EINVAL;

        ret = kvm_assign_ioeventfd_idx(kvm, bus_idx, args);
        if (ret)
                goto fail;

        /* When length is ignored, MMIO is also put on a separate bus, for
         * faster lookups.
         */
        if (!args->len && bus_idx == KVM_MMIO_BUS) {
                ret = kvm_assign_ioeventfd_idx(kvm, KVM_FAST_MMIO_BUS, args);
                if (ret < 0)
                        goto fast_fail;
        }

        return 0;

fast_fail:
        kvm_deassign_ioeventfd_idx(kvm, bus_idx, args);
fail:
        return ret;
}

int
kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
        if (args->flags & KVM_IOEVENTFD_FLAG_DEASSIGN)
                return kvm_deassign_ioeventfd(kvm, args);

        return kvm_assign_ioeventfd(kvm, args);
}