eventfd.c

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/*
 * 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 <[email protected]>
 *
 * 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/slab.h>

#include "iodev.h"

/*
 * --------------------------------------------------------------------
 * 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 __rcu *irq_entry;
    /* 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);
        kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
    } else
        kvm_set_irq(kvm, KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,
                irqfd->gsi, 1);
}

/*
 * 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 _irqfd *irqfd;

    resampler = container_of(kian, struct _irqfd_resampler, notifier);

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

    rcu_read_lock();

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

    rcu_read_unlock();
}

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_rcu();

    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);
        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;

    if (flags & POLLIN) {
        rcu_read_lock();
        irq = rcu_dereference(irqfd->irq_entry);
        /* An event has been signaled, inject an interrupt */
        if (irq)
            kvm_set_msi(irq, kvm, KVM_USERSPACE_IRQ_SOURCE_ID, 1);
        else
            schedule_work(&irqfd->inject);
        rcu_read_unlock();
    }

    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_irq_routing_table *irq_rt)
{
    struct kvm_kernel_irq_routing_entry *e;
    struct hlist_node *n;

    if (irqfd->gsi >= irq_rt->nr_rt_entries) {
        rcu_assign_pointer(irqfd->irq_entry, NULL);
        return;
    }

    hlist_for_each_entry(e, n, &irq_rt->map[irqfd->gsi], link) {
        /* Only fast-path MSI. */
        if (e->type == KVM_IRQ_ROUTING_MSI)
            rcu_assign_pointer(irqfd->irq_entry, e);
        else
            rcu_assign_pointer(irqfd->irq_entry, NULL);
    }
}

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

    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);

    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;
    }

    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, list) {
            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_rcu();

        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;
    }

    irq_rt = rcu_dereference_protected(kvm->irq_routing,
                       lockdep_is_held(&kvm->irqfds.lock));
    irqfd_update(kvm, irqfd, irq_rt);

    events = file->f_op->poll(file, &irqfd->pt);

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

    /*
     * 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);

    spin_unlock_irq(&kvm->irqfds.lock);

    /*
     * do not drop the file until the irqfd is fully initialized, otherwise
     * we might race against the POLLHUP
     */
    fput(file);

    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);

    if (!IS_ERR(file))
        fput(file);

    kfree(irqfd);
    return ret;
}

void
kvm_eventfd_init(struct kvm *kvm)
{
    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);
    INIT_LIST_HEAD(&kvm->ioeventfds);
}

/*
 * 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 rcu_assign_pointer 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).
             * It is paired with synchronize_rcu done by caller
             * of that function.
             */
            rcu_assign_pointer(irqfd->irq_entry, NULL);
            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);

}

/*
 * Change irq_routing and irqfd.
 * Caller must invoke synchronize_rcu afterwards.
 */
void kvm_irq_routing_update(struct kvm *kvm,
                struct kvm_irq_routing_table *irq_rt)
{
    struct _irqfd *irqfd;

    spin_lock_irq(&kvm->irqfds.lock);

    rcu_assign_pointer(kvm->irq_routing, irq_rt);

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

    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.
 */
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);

/*
 * --------------------------------------------------------------------
 * 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;
    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 && 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_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->addr == p->addr && _p->length == p->length &&
            (_p->wildcard || p->wildcard ||
             _p->datamatch == p->datamatch))
            return true;

    return false;
}

static int
kvm_assign_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
{
    int                       pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
    enum kvm_bus              bus_idx = pio ? KVM_PIO_BUS : KVM_MMIO_BUS;
    struct _ioeventfd        *p;
    struct eventfd_ctx       *eventfd;
    int                       ret;

    /* must be natural-word sized */
    switch (args->len) {
    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;

    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->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;

    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(struct kvm *kvm, struct kvm_ioeventfd *args)
{
    int                       pio = args->flags & KVM_IOEVENTFD_FLAG_PIO;
    enum kvm_bus              bus_idx = pio ? KVM_PIO_BUS : KVM_MMIO_BUS;
    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->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);
        ioeventfd_release(p);
        ret = 0;
        break;
    }

    mutex_unlock(&kvm->slots_lock);

    eventfd_ctx_put(eventfd);

    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);
}