vhost.c

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/* Copyright (C) 2009 Red Hat, Inc.
 * Copyright (C) 2006 Rusty Russell IBM Corporation
 *
 * Author: Michael S. Tsirkin <[email protected]>
 *
 * Inspiration, some code, and most witty comments come from
 * Documentation/virtual/lguest/lguest.c, by Rusty Russell
 *
 * This work is licensed under the terms of the GNU GPL, version 2.
 *
 * Generic code for virtio server in host kernel.
 */

#include <linux/eventfd.h>
#include <linux/vhost.h>
#include <linux/virtio_net.h>
#include <linux/mm.h>
#include <linux/mmu_context.h>
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/rcupdate.h>
#include <linux/poll.h>
#include <linux/file.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/kthread.h>
#include <linux/cgroup.h>

#include <linux/net.h>
#include <linux/if_packet.h>
#include <linux/if_arp.h>

#include "vhost.h"

enum {
    VHOST_MEMORY_MAX_NREGIONS = 64,
    VHOST_MEMORY_F_LOG = 0x1,
};

static unsigned vhost_zcopy_mask __read_mostly;

#define vhost_used_event(vq) ((u16 __user *)&vq->avail->ring[vq->num])
#define vhost_avail_event(vq) ((u16 __user *)&vq->used->ring[vq->num])

static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
                poll_table *pt)
{
    struct vhost_poll *poll;

    poll = container_of(pt, struct vhost_poll, table);
    poll->wqh = wqh;
    add_wait_queue(wqh, &poll->wait);
}

static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
                 void *key)
{
    struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait);

    if (!((unsigned long)key & poll->mask))
        return 0;

    vhost_poll_queue(poll);
    return 0;
}

void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
{
    INIT_LIST_HEAD(&work->node);
    work->fn = fn;
    init_waitqueue_head(&work->done);
    work->flushing = 0;
    work->queue_seq = work->done_seq = 0;
}

/* Init poll structure */
void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
             unsigned long mask, struct vhost_dev *dev)
{
    init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
    init_poll_funcptr(&poll->table, vhost_poll_func);
    poll->mask = mask;
    poll->dev = dev;

    vhost_work_init(&poll->work, fn);
}

/* Start polling a file. We add ourselves to file's wait queue. The caller must
 * keep a reference to a file until after vhost_poll_stop is called. */
void vhost_poll_start(struct vhost_poll *poll, struct file *file)
{
    unsigned long mask;

    mask = file->f_op->poll(file, &poll->table);
    if (mask)
        vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
}

/* Stop polling a file. After this function returns, it becomes safe to drop the
 * file reference. You must also flush afterwards. */
void vhost_poll_stop(struct vhost_poll *poll)
{
    remove_wait_queue(poll->wqh, &poll->wait);
}

static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,
                unsigned seq)
{
    int left;

    spin_lock_irq(&dev->work_lock);
    left = seq - work->done_seq;
    spin_unlock_irq(&dev->work_lock);
    return left <= 0;
}

static void vhost_work_flush(struct vhost_dev *dev, struct vhost_work *work)
{
    unsigned seq;
    int flushing;

    spin_lock_irq(&dev->work_lock);
    seq = work->queue_seq;
    work->flushing++;
    spin_unlock_irq(&dev->work_lock);
    wait_event(work->done, vhost_work_seq_done(dev, work, seq));
    spin_lock_irq(&dev->work_lock);
    flushing = --work->flushing;
    spin_unlock_irq(&dev->work_lock);
    BUG_ON(flushing < 0);
}

/* Flush any work that has been scheduled. When calling this, don't hold any
 * locks that are also used by the callback. */
void vhost_poll_flush(struct vhost_poll *poll)
{
    vhost_work_flush(poll->dev, &poll->work);
}

void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
{
    unsigned long flags;

    spin_lock_irqsave(&dev->work_lock, flags);
    if (list_empty(&work->node)) {
        list_add_tail(&work->node, &dev->work_list);
        work->queue_seq++;
        wake_up_process(dev->worker);
    }
    spin_unlock_irqrestore(&dev->work_lock, flags);
}

void vhost_poll_queue(struct vhost_poll *poll)
{
    vhost_work_queue(poll->dev, &poll->work);
}

static void vhost_vq_reset(struct vhost_dev *dev,
               struct vhost_virtqueue *vq)
{
    vq->num = 1;
    vq->desc = NULL;
    vq->avail = NULL;
    vq->used = NULL;
    vq->last_avail_idx = 0;
    vq->avail_idx = 0;
    vq->last_used_idx = 0;
    vq->signalled_used = 0;
    vq->signalled_used_valid = false;
    vq->used_flags = 0;
    vq->log_used = false;
    vq->log_addr = -1ull;
    vq->vhost_hlen = 0;
    vq->sock_hlen = 0;
    vq->private_data = NULL;
    vq->log_base = NULL;
    vq->error_ctx = NULL;
    vq->error = NULL;
    vq->kick = NULL;
    vq->call_ctx = NULL;
    vq->call = NULL;
    vq->log_ctx = NULL;
    vq->upend_idx = 0;
    vq->done_idx = 0;
    vq->ubufs = NULL;
}

static int vhost_worker(void *data)
{
    struct vhost_dev *dev = data;
    struct vhost_work *work = NULL;
    unsigned uninitialized_var(seq);
    mm_segment_t oldfs = get_fs();

    set_fs(USER_DS);
    use_mm(dev->mm);

    for (;;) {
        /* mb paired w/ kthread_stop */
        set_current_state(TASK_INTERRUPTIBLE);

        spin_lock_irq(&dev->work_lock);
        if (work) {
            work->done_seq = seq;
            if (work->flushing)
                wake_up_all(&work->done);
        }

        if (kthread_should_stop()) {
            spin_unlock_irq(&dev->work_lock);
            __set_current_state(TASK_RUNNING);
            break;
        }
        if (!list_empty(&dev->work_list)) {
            work = list_first_entry(&dev->work_list,
                        struct vhost_work, node);
            list_del_init(&work->node);
            seq = work->queue_seq;
        } else
            work = NULL;
        spin_unlock_irq(&dev->work_lock);

        if (work) {
            __set_current_state(TASK_RUNNING);
            work->fn(work);
            if (need_resched())
                schedule();
        } else
            schedule();

    }
    unuse_mm(dev->mm);
    set_fs(oldfs);
    return 0;
}

static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
{
    kfree(vq->indirect);
    vq->indirect = NULL;
    kfree(vq->log);
    vq->log = NULL;
    kfree(vq->heads);
    vq->heads = NULL;
    kfree(vq->ubuf_info);
    vq->ubuf_info = NULL;
}

void vhost_enable_zcopy(int vq)
{
    vhost_zcopy_mask |= 0x1 << vq;
}

/* Helper to allocate iovec buffers for all vqs. */
static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
{
    int i;
    bool zcopy;

    for (i = 0; i < dev->nvqs; ++i) {
        dev->vqs[i].indirect = kmalloc(sizeof *dev->vqs[i].indirect *
                           UIO_MAXIOV, GFP_KERNEL);
        dev->vqs[i].log = kmalloc(sizeof *dev->vqs[i].log * UIO_MAXIOV,
                      GFP_KERNEL);
        dev->vqs[i].heads = kmalloc(sizeof *dev->vqs[i].heads *
                        UIO_MAXIOV, GFP_KERNEL);
        zcopy = vhost_zcopy_mask & (0x1 << i);
        if (zcopy)
            dev->vqs[i].ubuf_info =
                kmalloc(sizeof *dev->vqs[i].ubuf_info *
                    UIO_MAXIOV, GFP_KERNEL);
        if (!dev->vqs[i].indirect || !dev->vqs[i].log ||
            !dev->vqs[i].heads ||
            (zcopy && !dev->vqs[i].ubuf_info))
            goto err_nomem;
    }
    return 0;

err_nomem:
    for (; i >= 0; --i)
        vhost_vq_free_iovecs(&dev->vqs[i]);
    return -ENOMEM;
}

static void vhost_dev_free_iovecs(struct vhost_dev *dev)
{
    int i;

    for (i = 0; i < dev->nvqs; ++i)
        vhost_vq_free_iovecs(&dev->vqs[i]);
}

long vhost_dev_init(struct vhost_dev *dev,
            struct vhost_virtqueue *vqs, int nvqs)
{
    int i;

    dev->vqs = vqs;
    dev->nvqs = nvqs;
    mutex_init(&dev->mutex);
    dev->log_ctx = NULL;
    dev->log_file = NULL;
    dev->memory = NULL;
    dev->mm = NULL;
    spin_lock_init(&dev->work_lock);
    INIT_LIST_HEAD(&dev->work_list);
    dev->worker = NULL;

    for (i = 0; i < dev->nvqs; ++i) {
        dev->vqs[i].log = NULL;
        dev->vqs[i].indirect = NULL;
        dev->vqs[i].heads = NULL;
        dev->vqs[i].ubuf_info = NULL;
        dev->vqs[i].dev = dev;
        mutex_init(&dev->vqs[i].mutex);
        vhost_vq_reset(dev, dev->vqs + i);
        if (dev->vqs[i].handle_kick)
            vhost_poll_init(&dev->vqs[i].poll,
                    dev->vqs[i].handle_kick, POLLIN, dev);
    }

    return 0;
}

/* Caller should have device mutex */
long vhost_dev_check_owner(struct vhost_dev *dev)
{
    /* Are you the owner? If not, I don't think you mean to do that */
    return dev->mm == current->mm ? 0 : -EPERM;
}

struct vhost_attach_cgroups_struct {
    struct vhost_work work;
    struct task_struct *owner;
    int ret;
};

static void vhost_attach_cgroups_work(struct vhost_work *work)
{
    struct vhost_attach_cgroups_struct *s;

    s = container_of(work, struct vhost_attach_cgroups_struct, work);
    s->ret = cgroup_attach_task_all(s->owner, current);
}

static int vhost_attach_cgroups(struct vhost_dev *dev)
{
    struct vhost_attach_cgroups_struct attach;

    attach.owner = current;
    vhost_work_init(&attach.work, vhost_attach_cgroups_work);
    vhost_work_queue(dev, &attach.work);
    vhost_work_flush(dev, &attach.work);
    return attach.ret;
}

/* Caller should have device mutex */
static long vhost_dev_set_owner(struct vhost_dev *dev)
{
    struct task_struct *worker;
    int err;

    /* Is there an owner already? */
    if (dev->mm) {
        err = -EBUSY;
        goto err_mm;
    }

    /* No owner, become one */
    dev->mm = get_task_mm(current);
    worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
    if (IS_ERR(worker)) {
        err = PTR_ERR(worker);
        goto err_worker;
    }

    dev->worker = worker;
    wake_up_process(worker);    /* avoid contributing to loadavg */

    err = vhost_attach_cgroups(dev);
    if (err)
        goto err_cgroup;

    err = vhost_dev_alloc_iovecs(dev);
    if (err)
        goto err_cgroup;

    return 0;
err_cgroup:
    kthread_stop(worker);
    dev->worker = NULL;
err_worker:
    if (dev->mm)
        mmput(dev->mm);
    dev->mm = NULL;
err_mm:
    return err;
}

/* Caller should have device mutex */
long vhost_dev_reset_owner(struct vhost_dev *dev)
{
    struct vhost_memory *memory;

    /* Restore memory to default empty mapping. */
    memory = kmalloc(offsetof(struct vhost_memory, regions), GFP_KERNEL);
    if (!memory)
        return -ENOMEM;

    vhost_dev_cleanup(dev, true);

    memory->nregions = 0;
    RCU_INIT_POINTER(dev->memory, memory);
    return 0;
}

/* In case of DMA done not in order in lower device driver for some reason.
 * upend_idx is used to track end of used idx, done_idx is used to track head
 * of used idx. Once lower device DMA done contiguously, we will signal KVM
 * guest used idx.
 */
int vhost_zerocopy_signal_used(struct vhost_virtqueue *vq)
{
    int i;
    int j = 0;

    for (i = vq->done_idx; i != vq->upend_idx; i = (i + 1) % UIO_MAXIOV) {
        if ((vq->heads[i].len == VHOST_DMA_DONE_LEN)) {
            vq->heads[i].len = VHOST_DMA_CLEAR_LEN;
            vhost_add_used_and_signal(vq->dev, vq,
                          vq->heads[i].id, 0);
            ++j;
        } else
            break;
    }
    if (j)
        vq->done_idx = i;
    return j;
}

/* Caller should have device mutex if and only if locked is set */
void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
{
    int i;

    for (i = 0; i < dev->nvqs; ++i) {
        if (dev->vqs[i].kick && dev->vqs[i].handle_kick) {
            vhost_poll_stop(&dev->vqs[i].poll);
            vhost_poll_flush(&dev->vqs[i].poll);
        }
        /* Wait for all lower device DMAs done. */
        if (dev->vqs[i].ubufs)
            vhost_ubuf_put_and_wait(dev->vqs[i].ubufs);

        /* Signal guest as appropriate. */
        vhost_zerocopy_signal_used(&dev->vqs[i]);

        if (dev->vqs[i].error_ctx)
            eventfd_ctx_put(dev->vqs[i].error_ctx);
        if (dev->vqs[i].error)
            fput(dev->vqs[i].error);
        if (dev->vqs[i].kick)
            fput(dev->vqs[i].kick);
        if (dev->vqs[i].call_ctx)
            eventfd_ctx_put(dev->vqs[i].call_ctx);
        if (dev->vqs[i].call)
            fput(dev->vqs[i].call);
        vhost_vq_reset(dev, dev->vqs + i);
    }
    vhost_dev_free_iovecs(dev);
    if (dev->log_ctx)
        eventfd_ctx_put(dev->log_ctx);
    dev->log_ctx = NULL;
    if (dev->log_file)
        fput(dev->log_file);
    dev->log_file = NULL;
    /* No one will access memory at this point */
    kfree(rcu_dereference_protected(dev->memory,
                    locked ==
                        lockdep_is_held(&dev->mutex)));
    RCU_INIT_POINTER(dev->memory, NULL);
    WARN_ON(!list_empty(&dev->work_list));
    if (dev->worker) {
        kthread_stop(dev->worker);
        dev->worker = NULL;
    }
    if (dev->mm)
        mmput(dev->mm);
    dev->mm = NULL;
}

static int log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
{
    u64 a = addr / VHOST_PAGE_SIZE / 8;

    /* Make sure 64 bit math will not overflow. */
    if (a > ULONG_MAX - (unsigned long)log_base ||
        a + (unsigned long)log_base > ULONG_MAX)
        return 0;

    return access_ok(VERIFY_WRITE, log_base + a,
             (sz + VHOST_PAGE_SIZE * 8 - 1) / VHOST_PAGE_SIZE / 8);
}

/* Caller should have vq mutex and device mutex. */
static int vq_memory_access_ok(void __user *log_base, struct vhost_memory *mem,
                   int log_all)
{
    int i;

    if (!mem)
        return 0;

    for (i = 0; i < mem->nregions; ++i) {
        struct vhost_memory_region *m = mem->regions + i;
        unsigned long a = m->userspace_addr;
        if (m->memory_size > ULONG_MAX)
            return 0;
        else if (!access_ok(VERIFY_WRITE, (void __user *)a,
                    m->memory_size))
            return 0;
        else if (log_all && !log_access_ok(log_base,
                           m->guest_phys_addr,
                           m->memory_size))
            return 0;
    }
    return 1;
}

/* Can we switch to this memory table? */
/* Caller should have device mutex but not vq mutex */
static int memory_access_ok(struct vhost_dev *d, struct vhost_memory *mem,
                int log_all)
{
    int i;

    for (i = 0; i < d->nvqs; ++i) {
        int ok;
        mutex_lock(&d->vqs[i].mutex);
        /* If ring is inactive, will check when it's enabled. */
        if (d->vqs[i].private_data)
            ok = vq_memory_access_ok(d->vqs[i].log_base, mem,
                         log_all);
        else
            ok = 1;
        mutex_unlock(&d->vqs[i].mutex);
        if (!ok)
            return 0;
    }
    return 1;
}

static int vq_access_ok(struct vhost_dev *d, unsigned int num,
            struct vring_desc __user *desc,
            struct vring_avail __user *avail,
            struct vring_used __user *used)
{
    size_t s = vhost_has_feature(d, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
    return access_ok(VERIFY_READ, desc, num * sizeof *desc) &&
           access_ok(VERIFY_READ, avail,
             sizeof *avail + num * sizeof *avail->ring + s) &&
           access_ok(VERIFY_WRITE, used,
            sizeof *used + num * sizeof *used->ring + s);
}

/* Can we log writes? */
/* Caller should have device mutex but not vq mutex */
int vhost_log_access_ok(struct vhost_dev *dev)
{
    struct vhost_memory *mp;

    mp = rcu_dereference_protected(dev->memory,
                       lockdep_is_held(&dev->mutex));
    return memory_access_ok(dev, mp, 1);
}

/* Verify access for write logging. */
/* Caller should have vq mutex and device mutex */
static int vq_log_access_ok(struct vhost_dev *d, struct vhost_virtqueue *vq,
                void __user *log_base)
{
    struct vhost_memory *mp;
    size_t s = vhost_has_feature(d, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;

    mp = rcu_dereference_protected(vq->dev->memory,
                       lockdep_is_held(&vq->mutex));
    return vq_memory_access_ok(log_base, mp,
                vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
        (!vq->log_used || log_access_ok(log_base, vq->log_addr,
                    sizeof *vq->used +
                    vq->num * sizeof *vq->used->ring + s));
}

/* Can we start vq? */
/* Caller should have vq mutex and device mutex */
int vhost_vq_access_ok(struct vhost_virtqueue *vq)
{
    return vq_access_ok(vq->dev, vq->num, vq->desc, vq->avail, vq->used) &&
        vq_log_access_ok(vq->dev, vq, vq->log_base);
}

static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
{
    struct vhost_memory mem, *newmem, *oldmem;
    unsigned long size = offsetof(struct vhost_memory, regions);

    if (copy_from_user(&mem, m, size))
        return -EFAULT;
    if (mem.padding)
        return -EOPNOTSUPP;
    if (mem.nregions > VHOST_MEMORY_MAX_NREGIONS)
        return -E2BIG;
    newmem = kmalloc(size + mem.nregions * sizeof *m->regions, GFP_KERNEL);
    if (!newmem)
        return -ENOMEM;

    memcpy(newmem, &mem, size);
    if (copy_from_user(newmem->regions, m->regions,
               mem.nregions * sizeof *m->regions)) {
        kfree(newmem);
        return -EFAULT;
    }

    if (!memory_access_ok(d, newmem,
                  vhost_has_feature(d, VHOST_F_LOG_ALL))) {
        kfree(newmem);
        return -EFAULT;
    }
    oldmem = rcu_dereference_protected(d->memory,
                       lockdep_is_held(&d->mutex));
    rcu_assign_pointer(d->memory, newmem);
    synchronize_rcu();
    kfree(oldmem);
    return 0;
}

static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
{
    struct file *eventfp, *filep = NULL;
    bool pollstart = false, pollstop = false;
    struct eventfd_ctx *ctx = NULL;
    u32 __user *idxp = argp;
    struct vhost_virtqueue *vq;
    struct vhost_vring_state s;
    struct vhost_vring_file f;
    struct vhost_vring_addr a;
    u32 idx;
    long r;

    r = get_user(idx, idxp);
    if (r < 0)
        return r;
    if (idx >= d->nvqs)
        return -ENOBUFS;

    vq = d->vqs + idx;

    mutex_lock(&vq->mutex);

    switch (ioctl) {
    case VHOST_SET_VRING_NUM:
        /* Resizing ring with an active backend?
         * You don't want to do that. */
        if (vq->private_data) {
            r = -EBUSY;
            break;
        }
        if (copy_from_user(&s, argp, sizeof s)) {
            r = -EFAULT;
            break;
        }
        if (!s.num || s.num > 0xffff || (s.num & (s.num - 1))) {
            r = -EINVAL;
            break;
        }
        vq->num = s.num;
        break;
    case VHOST_SET_VRING_BASE:
        /* Moving base with an active backend?
         * You don't want to do that. */
        if (vq->private_data) {
            r = -EBUSY;
            break;
        }
        if (copy_from_user(&s, argp, sizeof s)) {
            r = -EFAULT;
            break;
        }
        if (s.num > 0xffff) {
            r = -EINVAL;
            break;
        }
        vq->last_avail_idx = s.num;
        /* Forget the cached index value. */
        vq->avail_idx = vq->last_avail_idx;
        break;
    case VHOST_GET_VRING_BASE:
        s.index = idx;
        s.num = vq->last_avail_idx;
        if (copy_to_user(argp, &s, sizeof s))
            r = -EFAULT;
        break;
    case VHOST_SET_VRING_ADDR:
        if (copy_from_user(&a, argp, sizeof a)) {
            r = -EFAULT;
            break;
        }
        if (a.flags & ~(0x1 << VHOST_VRING_F_LOG)) {
            r = -EOPNOTSUPP;
            break;
        }
        /* For 32bit, verify that the top 32bits of the user
           data are set to zero. */
        if ((u64)(unsigned long)a.desc_user_addr != a.desc_user_addr ||
            (u64)(unsigned long)a.used_user_addr != a.used_user_addr ||
            (u64)(unsigned long)a.avail_user_addr != a.avail_user_addr) {
            r = -EFAULT;
            break;
        }
        if ((a.avail_user_addr & (sizeof *vq->avail->ring - 1)) ||
            (a.used_user_addr & (sizeof *vq->used->ring - 1)) ||
            (a.log_guest_addr & (sizeof *vq->used->ring - 1))) {
            r = -EINVAL;
            break;
        }

        /* We only verify access here if backend is configured.
         * If it is not, we don't as size might not have been setup.
         * We will verify when backend is configured. */
        if (vq->private_data) {
            if (!vq_access_ok(d, vq->num,
                (void __user *)(unsigned long)a.desc_user_addr,
                (void __user *)(unsigned long)a.avail_user_addr,
                (void __user *)(unsigned long)a.used_user_addr)) {
                r = -EINVAL;
                break;
            }

            /* Also validate log access for used ring if enabled. */
            if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
                !log_access_ok(vq->log_base, a.log_guest_addr,
                       sizeof *vq->used +
                       vq->num * sizeof *vq->used->ring)) {
                r = -EINVAL;
                break;
            }
        }

        vq->log_used = !!(a.flags & (0x1 << VHOST_VRING_F_LOG));
        vq->desc = (void __user *)(unsigned long)a.desc_user_addr;
        vq->avail = (void __user *)(unsigned long)a.avail_user_addr;
        vq->log_addr = a.log_guest_addr;
        vq->used = (void __user *)(unsigned long)a.used_user_addr;
        break;
    case VHOST_SET_VRING_KICK:
        if (copy_from_user(&f, argp, sizeof f)) {
            r = -EFAULT;
            break;
        }
        eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
        if (IS_ERR(eventfp)) {
            r = PTR_ERR(eventfp);
            break;
        }
        if (eventfp != vq->kick) {
            pollstop = (filep = vq->kick) != NULL;
            pollstart = (vq->kick = eventfp) != NULL;
        } else
            filep = eventfp;
        break;
    case VHOST_SET_VRING_CALL:
        if (copy_from_user(&f, argp, sizeof f)) {
            r = -EFAULT;
            break;
        }
        eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
        if (IS_ERR(eventfp)) {
            r = PTR_ERR(eventfp);
            break;
        }
        if (eventfp != vq->call) {
            filep = vq->call;
            ctx = vq->call_ctx;
            vq->call = eventfp;
            vq->call_ctx = eventfp ?
                eventfd_ctx_fileget(eventfp) : NULL;
        } else
            filep = eventfp;
        break;
    case VHOST_SET_VRING_ERR:
        if (copy_from_user(&f, argp, sizeof f)) {
            r = -EFAULT;
            break;
        }
        eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
        if (IS_ERR(eventfp)) {
            r = PTR_ERR(eventfp);
            break;
        }
        if (eventfp != vq->error) {
            filep = vq->error;
            vq->error = eventfp;
            ctx = vq->error_ctx;
            vq->error_ctx = eventfp ?
                eventfd_ctx_fileget(eventfp) : NULL;
        } else
            filep = eventfp;
        break;
    default:
        r = -ENOIOCTLCMD;
    }

    if (pollstop && vq->handle_kick)
        vhost_poll_stop(&vq->poll);

    if (ctx)
        eventfd_ctx_put(ctx);
    if (filep)
        fput(filep);

    if (pollstart && vq->handle_kick)
        vhost_poll_start(&vq->poll, vq->kick);

    mutex_unlock(&vq->mutex);

    if (pollstop && vq->handle_kick)
        vhost_poll_flush(&vq->poll);
    return r;
}

/* Caller must have device mutex */
long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
{
    void __user *argp = (void __user *)arg;
    struct file *eventfp, *filep = NULL;
    struct eventfd_ctx *ctx = NULL;
    u64 p;
    long r;
    int i, fd;

    /* If you are not the owner, you can become one */
    if (ioctl == VHOST_SET_OWNER) {
        r = vhost_dev_set_owner(d);
        goto done;
    }

    /* You must be the owner to do anything else */
    r = vhost_dev_check_owner(d);
    if (r)
        goto done;

    switch (ioctl) {
    case VHOST_SET_MEM_TABLE:
        r = vhost_set_memory(d, argp);
        break;
    case VHOST_SET_LOG_BASE:
        if (copy_from_user(&p, argp, sizeof p)) {
            r = -EFAULT;
            break;
        }
        if ((u64)(unsigned long)p != p) {
            r = -EFAULT;
            break;
        }
        for (i = 0; i < d->nvqs; ++i) {
            struct vhost_virtqueue *vq;
            void __user *base = (void __user *)(unsigned long)p;
            vq = d->vqs + i;
            mutex_lock(&vq->mutex);
            /* If ring is inactive, will check when it's enabled. */
            if (vq->private_data && !vq_log_access_ok(d, vq, base))
                r = -EFAULT;
            else
                vq->log_base = base;
            mutex_unlock(&vq->mutex);
        }
        break;
    case VHOST_SET_LOG_FD:
        r = get_user(fd, (int __user *)argp);
        if (r < 0)
            break;
        eventfp = fd == -1 ? NULL : eventfd_fget(fd);
        if (IS_ERR(eventfp)) {
            r = PTR_ERR(eventfp);
            break;
        }
        if (eventfp != d->log_file) {
            filep = d->log_file;
            ctx = d->log_ctx;
            d->log_ctx = eventfp ?
                eventfd_ctx_fileget(eventfp) : NULL;
        } else
            filep = eventfp;
        for (i = 0; i < d->nvqs; ++i) {
            mutex_lock(&d->vqs[i].mutex);
            d->vqs[i].log_ctx = d->log_ctx;
            mutex_unlock(&d->vqs[i].mutex);
        }
        if (ctx)
            eventfd_ctx_put(ctx);
        if (filep)
            fput(filep);
        break;
    default:
        r = vhost_set_vring(d, ioctl, argp);
        break;
    }
done:
    return r;
}

static const struct vhost_memory_region *find_region(struct vhost_memory *mem,
                             __u64 addr, __u32 len)
{
    struct vhost_memory_region *reg;
    int i;

    /* linear search is not brilliant, but we really have on the order of 6
     * regions in practice */
    for (i = 0; i < mem->nregions; ++i) {
        reg = mem->regions + i;
        if (reg->guest_phys_addr <= addr &&
            reg->guest_phys_addr + reg->memory_size - 1 >= addr)
            return reg;
    }
    return NULL;
}

/* TODO: This is really inefficient.  We need something like get_user()
 * (instruction directly accesses the data, with an exception table entry
 * returning -EFAULT). See Documentation/x86/exception-tables.txt.
 */
static int set_bit_to_user(int nr, void __user *addr)
{
    unsigned long log = (unsigned long)addr;
    struct page *page;
    void *base;
    int bit = nr + (log % PAGE_SIZE) * 8;
    int r;

    r = get_user_pages_fast(log, 1, 1, &page);
    if (r < 0)
        return r;
    BUG_ON(r != 1);
    base = kmap_atomic(page);
    set_bit(bit, base);
    kunmap_atomic(base);
    set_page_dirty_lock(page);
    put_page(page);
    return 0;
}

static int log_write(void __user *log_base,
             u64 write_address, u64 write_length)
{
    u64 write_page = write_address / VHOST_PAGE_SIZE;
    int r;

    if (!write_length)
        return 0;
    write_length += write_address % VHOST_PAGE_SIZE;
    for (;;) {
        u64 base = (u64)(unsigned long)log_base;
        u64 log = base + write_page / 8;
        int bit = write_page % 8;
        if ((u64)(unsigned long)log != log)
            return -EFAULT;
        r = set_bit_to_user(bit, (void __user *)(unsigned long)log);
        if (r < 0)
            return r;
        if (write_length <= VHOST_PAGE_SIZE)
            break;
        write_length -= VHOST_PAGE_SIZE;
        write_page += 1;
    }
    return r;
}

int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
            unsigned int log_num, u64 len)
{
    int i, r;

    /* Make sure data written is seen before log. */
    smp_wmb();
    for (i = 0; i < log_num; ++i) {
        u64 l = min(log[i].len, len);
        r = log_write(vq->log_base, log[i].addr, l);
        if (r < 0)
            return r;
        len -= l;
        if (!len) {
            if (vq->log_ctx)
                eventfd_signal(vq->log_ctx, 1);
            return 0;
        }
    }
    /* Length written exceeds what we have stored. This is a bug. */
    BUG();
    return 0;
}

static int vhost_update_used_flags(struct vhost_virtqueue *vq)
{
    void __user *used;
    if (__put_user(vq->used_flags, &vq->used->flags) < 0)
        return -EFAULT;
    if (unlikely(vq->log_used)) {
        /* Make sure the flag is seen before log. */
        smp_wmb();
        /* Log used flag write. */
        used = &vq->used->flags;
        log_write(vq->log_base, vq->log_addr +
              (used - (void __user *)vq->used),
              sizeof vq->used->flags);
        if (vq->log_ctx)
            eventfd_signal(vq->log_ctx, 1);
    }
    return 0;
}

static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event)
{
    if (__put_user(vq->avail_idx, vhost_avail_event(vq)))
        return -EFAULT;
    if (unlikely(vq->log_used)) {
        void __user *used;
        /* Make sure the event is seen before log. */
        smp_wmb();
        /* Log avail event write */
        used = vhost_avail_event(vq);
        log_write(vq->log_base, vq->log_addr +
              (used - (void __user *)vq->used),
              sizeof *vhost_avail_event(vq));
        if (vq->log_ctx)
            eventfd_signal(vq->log_ctx, 1);
    }
    return 0;
}

int vhost_init_used(struct vhost_virtqueue *vq)
{
    int r;
    if (!vq->private_data)
        return 0;

    r = vhost_update_used_flags(vq);
    if (r)
        return r;
    vq->signalled_used_valid = false;
    return get_user(vq->last_used_idx, &vq->used->idx);
}

static int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
              struct iovec iov[], int iov_size)
{
    const struct vhost_memory_region *reg;
    struct vhost_memory *mem;
    struct iovec *_iov;
    u64 s = 0;
    int ret = 0;

    rcu_read_lock();

    mem = rcu_dereference(dev->memory);
    while ((u64)len > s) {
        u64 size;
        if (unlikely(ret >= iov_size)) {
            ret = -ENOBUFS;
            break;
        }
        reg = find_region(mem, addr, len);
        if (unlikely(!reg)) {
            ret = -EFAULT;
            break;
        }
        _iov = iov + ret;
        size = reg->memory_size - addr + reg->guest_phys_addr;
        _iov->iov_len = min((u64)len - s, size);
        _iov->iov_base = (void __user *)(unsigned long)
            (reg->userspace_addr + addr - reg->guest_phys_addr);
        s += size;
        addr += size;
        ++ret;
    }

    rcu_read_unlock();
    return ret;
}

/* Each buffer in the virtqueues is actually a chain of descriptors.  This
 * function returns the next descriptor in the chain,
 * or -1U if we're at the end. */
static unsigned next_desc(struct vring_desc *desc)
{
    unsigned int next;

    /* If this descriptor says it doesn't chain, we're done. */
    if (!(desc->flags & VRING_DESC_F_NEXT))
        return -1U;

    /* Check they're not leading us off end of descriptors. */
    next = desc->next;
    /* Make sure compiler knows to grab that: we don't want it changing! */
    /* We will use the result as an index in an array, so most
     * architectures only need a compiler barrier here. */
    read_barrier_depends();

    return next;
}

static int get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
            struct iovec iov[], unsigned int iov_size,
            unsigned int *out_num, unsigned int *in_num,
            struct vhost_log *log, unsigned int *log_num,
            struct vring_desc *indirect)
{
    struct vring_desc desc;
    unsigned int i = 0, count, found = 0;
    int ret;

    /* Sanity check */
    if (unlikely(indirect->len % sizeof desc)) {
        vq_err(vq, "Invalid length in indirect descriptor: "
               "len 0x%llx not multiple of 0x%zx\n",
               (unsigned long long)indirect->len,
               sizeof desc);
        return -EINVAL;
    }

    ret = translate_desc(dev, indirect->addr, indirect->len, vq->indirect,
                 UIO_MAXIOV);
    if (unlikely(ret < 0)) {
        vq_err(vq, "Translation failure %d in indirect.\n", ret);
        return ret;
    }

    /* We will use the result as an address to read from, so most
     * architectures only need a compiler barrier here. */
    read_barrier_depends();

    count = indirect->len / sizeof desc;
    /* Buffers are chained via a 16 bit next field, so
     * we can have at most 2^16 of these. */
    if (unlikely(count > USHRT_MAX + 1)) {
        vq_err(vq, "Indirect buffer length too big: %d\n",
               indirect->len);
        return -E2BIG;
    }

    do {
        unsigned iov_count = *in_num + *out_num;
        if (unlikely(++found > count)) {
            vq_err(vq, "Loop detected: last one at %u "
                   "indirect size %u\n",
                   i, count);
            return -EINVAL;
        }
        if (unlikely(memcpy_fromiovec((unsigned char *)&desc,
                          vq->indirect, sizeof desc))) {
            vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
                   i, (size_t)indirect->addr + i * sizeof desc);
            return -EINVAL;
        }
        if (unlikely(desc.flags & VRING_DESC_F_INDIRECT)) {
            vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
                   i, (size_t)indirect->addr + i * sizeof desc);
            return -EINVAL;
        }

        ret = translate_desc(dev, desc.addr, desc.len, iov + iov_count,
                     iov_size - iov_count);
        if (unlikely(ret < 0)) {
            vq_err(vq, "Translation failure %d indirect idx %d\n",
                   ret, i);
            return ret;
        }
        /* If this is an input descriptor, increment that count. */
        if (desc.flags & VRING_DESC_F_WRITE) {
            *in_num += ret;
            if (unlikely(log)) {
                log[*log_num].addr = desc.addr;
                log[*log_num].len = desc.len;
                ++*log_num;
            }
        } else {
            /* If it's an output descriptor, they're all supposed
             * to come before any input descriptors. */
            if (unlikely(*in_num)) {
                vq_err(vq, "Indirect descriptor "
                       "has out after in: idx %d\n", i);
                return -EINVAL;
            }
            *out_num += ret;
        }
    } while ((i = next_desc(&desc)) != -1);
    return 0;
}

/* This looks in the virtqueue and for the first available buffer, and converts
 * it to an iovec for convenient access.  Since descriptors consist of some
 * number of output then some number of input descriptors, it's actually two
 * iovecs, but we pack them into one and note how many of each there were.
 *
 * This function returns the descriptor number found, or vq->num (which is
 * never a valid descriptor number) if none was found.  A negative code is
 * returned on error. */
int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
              struct iovec iov[], unsigned int iov_size,
              unsigned int *out_num, unsigned int *in_num,
              struct vhost_log *log, unsigned int *log_num)
{
    struct vring_desc desc;
    unsigned int i, head, found = 0;
    u16 last_avail_idx;
    int ret;

    /* Check it isn't doing very strange things with descriptor numbers. */
    last_avail_idx = vq->last_avail_idx;
    if (unlikely(__get_user(vq->avail_idx, &vq->avail->idx))) {
        vq_err(vq, "Failed to access avail idx at %p\n",
               &vq->avail->idx);
        return -EFAULT;
    }

    if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) {
        vq_err(vq, "Guest moved used index from %u to %u",
               last_avail_idx, vq->avail_idx);
        return -EFAULT;
    }

    /* If there's nothing new since last we looked, return invalid. */
    if (vq->avail_idx == last_avail_idx)
        return vq->num;

    /* Only get avail ring entries after they have been exposed by guest. */
    smp_rmb();

    /* Grab the next descriptor number they're advertising, and increment
     * the index we've seen. */
    if (unlikely(__get_user(head,
                &vq->avail->ring[last_avail_idx % vq->num]))) {
        vq_err(vq, "Failed to read head: idx %d address %p\n",
               last_avail_idx,
               &vq->avail->ring[last_avail_idx % vq->num]);
        return -EFAULT;
    }

    /* If their number is silly, that's an error. */
    if (unlikely(head >= vq->num)) {
        vq_err(vq, "Guest says index %u > %u is available",
               head, vq->num);
        return -EINVAL;
    }

    /* When we start there are none of either input nor output. */
    *out_num = *in_num = 0;
    if (unlikely(log))
        *log_num = 0;

    i = head;
    do {
        unsigned iov_count = *in_num + *out_num;
        if (unlikely(i >= vq->num)) {
            vq_err(vq, "Desc index is %u > %u, head = %u",
                   i, vq->num, head);
            return -EINVAL;
        }
        if (unlikely(++found > vq->num)) {
            vq_err(vq, "Loop detected: last one at %u "
                   "vq size %u head %u\n",
                   i, vq->num, head);
            return -EINVAL;
        }
        ret = __copy_from_user(&desc, vq->desc + i, sizeof desc);
        if (unlikely(ret)) {
            vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
                   i, vq->desc + i);
            return -EFAULT;
        }
        if (desc.flags & VRING_DESC_F_INDIRECT) {
            ret = get_indirect(dev, vq, iov, iov_size,
                       out_num, in_num,
                       log, log_num, &desc);
            if (unlikely(ret < 0)) {
                vq_err(vq, "Failure detected "
                       "in indirect descriptor at idx %d\n", i);
                return ret;
            }
            continue;
        }

        ret = translate_desc(dev, desc.addr, desc.len, iov + iov_count,
                     iov_size - iov_count);
        if (unlikely(ret < 0)) {
            vq_err(vq, "Translation failure %d descriptor idx %d\n",
                   ret, i);
            return ret;
        }
        if (desc.flags & VRING_DESC_F_WRITE) {
            /* If this is an input descriptor,
             * increment that count. */
            *in_num += ret;
            if (unlikely(log)) {
                log[*log_num].addr = desc.addr;
                log[*log_num].len = desc.len;
                ++*log_num;
            }
        } else {
            /* If it's an output descriptor, they're all supposed
             * to come before any input descriptors. */
            if (unlikely(*in_num)) {
                vq_err(vq, "Descriptor has out after in: "
                       "idx %d\n", i);
                return -EINVAL;
            }
            *out_num += ret;
        }
    } while ((i = next_desc(&desc)) != -1);

    /* On success, increment avail index. */
    vq->last_avail_idx++;

    /* Assume notifications from guest are disabled at this point,
     * if they aren't we would need to update avail_event index. */
    BUG_ON(!(vq->used_flags & VRING_USED_F_NO_NOTIFY));
    return head;
}

/* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
{
    vq->last_avail_idx -= n;
}

/* After we've used one of their buffers, we tell them about it.  We'll then
 * want to notify the guest, using eventfd. */
int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
{
    struct vring_used_elem __user *used;

    /* The virtqueue contains a ring of used buffers.  Get a pointer to the
     * next entry in that used ring. */
    used = &vq->used->ring[vq->last_used_idx % vq->num];
    if (__put_user(head, &used->id)) {
        vq_err(vq, "Failed to write used id");
        return -EFAULT;
    }
    if (__put_user(len, &used->len)) {
        vq_err(vq, "Failed to write used len");
        return -EFAULT;
    }
    /* Make sure buffer is written before we update index. */
    smp_wmb();
    if (__put_user(vq->last_used_idx + 1, &vq->used->idx)) {
        vq_err(vq, "Failed to increment used idx");
        return -EFAULT;
    }
    if (unlikely(vq->log_used)) {
        /* Make sure data is seen before log. */
        smp_wmb();
        /* Log used ring entry write. */
        log_write(vq->log_base,
              vq->log_addr +
               ((void __user *)used - (void __user *)vq->used),
              sizeof *used);
        /* Log used index update. */
        log_write(vq->log_base,
              vq->log_addr + offsetof(struct vring_used, idx),
              sizeof vq->used->idx);
        if (vq->log_ctx)
            eventfd_signal(vq->log_ctx, 1);
    }
    vq->last_used_idx++;
    /* If the driver never bothers to signal in a very long while,
     * used index might wrap around. If that happens, invalidate
     * signalled_used index we stored. TODO: make sure driver
     * signals at least once in 2^16 and remove this. */
    if (unlikely(vq->last_used_idx == vq->signalled_used))
        vq->signalled_used_valid = false;
    return 0;
}

static int __vhost_add_used_n(struct vhost_virtqueue *vq,
                struct vring_used_elem *heads,
                unsigned count)
{
    struct vring_used_elem __user *used;
    u16 old, new;
    int start;

    start = vq->last_used_idx % vq->num;
    used = vq->used->ring + start;
    if (__copy_to_user(used, heads, count * sizeof *used)) {
        vq_err(vq, "Failed to write used");
        return -EFAULT;
    }
    if (unlikely(vq->log_used)) {
        /* Make sure data is seen before log. */
        smp_wmb();
        /* Log used ring entry write. */
        log_write(vq->log_base,
              vq->log_addr +
               ((void __user *)used - (void __user *)vq->used),
              count * sizeof *used);
    }
    old = vq->last_used_idx;
    new = (vq->last_used_idx += count);
    /* If the driver never bothers to signal in a very long while,
     * used index might wrap around. If that happens, invalidate
     * signalled_used index we stored. TODO: make sure driver
     * signals at least once in 2^16 and remove this. */
    if (unlikely((u16)(new - vq->signalled_used) < (u16)(new - old)))
        vq->signalled_used_valid = false;
    return 0;
}

/* After we've used one of their buffers, we tell them about it.  We'll then
 * want to notify the guest, using eventfd. */
int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
             unsigned count)
{
    int start, n, r;

    start = vq->last_used_idx % vq->num;
    n = vq->num - start;
    if (n < count) {
        r = __vhost_add_used_n(vq, heads, n);
        if (r < 0)
            return r;
        heads += n;
        count -= n;
    }
    r = __vhost_add_used_n(vq, heads, count);

    /* Make sure buffer is written before we update index. */
    smp_wmb();
    if (put_user(vq->last_used_idx, &vq->used->idx)) {
        vq_err(vq, "Failed to increment used idx");
        return -EFAULT;
    }
    if (unlikely(vq->log_used)) {
        /* Log used index update. */
        log_write(vq->log_base,
              vq->log_addr + offsetof(struct vring_used, idx),
              sizeof vq->used->idx);
        if (vq->log_ctx)
            eventfd_signal(vq->log_ctx, 1);
    }
    return r;
}

static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
    __u16 old, new, event;
    bool v;
    /* Flush out used index updates. This is paired
     * with the barrier that the Guest executes when enabling
     * interrupts. */
    smp_mb();

    if (vhost_has_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY) &&
        unlikely(vq->avail_idx == vq->last_avail_idx))
        return true;

    if (!vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
        __u16 flags;
        if (__get_user(flags, &vq->avail->flags)) {
            vq_err(vq, "Failed to get flags");
            return true;
        }
        return !(flags & VRING_AVAIL_F_NO_INTERRUPT);
    }
    old = vq->signalled_used;
    v = vq->signalled_used_valid;
    new = vq->signalled_used = vq->last_used_idx;
    vq->signalled_used_valid = true;

    if (unlikely(!v))
        return true;

    if (get_user(event, vhost_used_event(vq))) {
        vq_err(vq, "Failed to get used event idx");
        return true;
    }
    return vring_need_event(event, new, old);
}

/* This actually signals the guest, using eventfd. */
void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
    /* Signal the Guest tell them we used something up. */
    if (vq->call_ctx && vhost_notify(dev, vq))
        eventfd_signal(vq->call_ctx, 1);
}

/* And here's the combo meal deal.  Supersize me! */
void vhost_add_used_and_signal(struct vhost_dev *dev,
                   struct vhost_virtqueue *vq,
                   unsigned int head, int len)
{
    vhost_add_used(vq, head, len);
    vhost_signal(dev, vq);
}

/* multi-buffer version of vhost_add_used_and_signal */
void vhost_add_used_and_signal_n(struct vhost_dev *dev,
                 struct vhost_virtqueue *vq,
                 struct vring_used_elem *heads, unsigned count)
{
    vhost_add_used_n(vq, heads, count);
    vhost_signal(dev, vq);
}

/* OK, now we need to know about added descriptors. */
bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
    u16 avail_idx;
    int r;

    if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
        return false;
    vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
    if (!vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
        r = vhost_update_used_flags(vq);
        if (r) {
            vq_err(vq, "Failed to enable notification at %p: %d\n",
                   &vq->used->flags, r);
            return false;
        }
    } else {
        r = vhost_update_avail_event(vq, vq->avail_idx);
        if (r) {
            vq_err(vq, "Failed to update avail event index at %p: %d\n",
                   vhost_avail_event(vq), r);
            return false;
        }
    }
    /* They could have slipped one in as we were doing that: make
     * sure it's written, then check again. */
    smp_mb();
    r = __get_user(avail_idx, &vq->avail->idx);
    if (r) {
        vq_err(vq, "Failed to check avail idx at %p: %d\n",
               &vq->avail->idx, r);
        return false;
    }

    return avail_idx != vq->avail_idx;
}

/* We don't need to be notified again. */
void vhost_disable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
    int r;

    if (vq->used_flags & VRING_USED_F_NO_NOTIFY)
        return;
    vq->used_flags |= VRING_USED_F_NO_NOTIFY;
    if (!vhost_has_feature(dev, VIRTIO_RING_F_EVENT_IDX)) {
        r = vhost_update_used_flags(vq);
        if (r)
            vq_err(vq, "Failed to enable notification at %p: %d\n",
                   &vq->used->flags, r);
    }
}

static void vhost_zerocopy_done_signal(struct kref *kref)
{
    struct vhost_ubuf_ref *ubufs = container_of(kref, struct vhost_ubuf_ref,
                            kref);
    wake_up(&ubufs->wait);
}

struct vhost_ubuf_ref *vhost_ubuf_alloc(struct vhost_virtqueue *vq,
                    bool zcopy)
{
    struct vhost_ubuf_ref *ubufs;
    /* No zero copy backend? Nothing to count. */
    if (!zcopy)
        return NULL;
    ubufs = kmalloc(sizeof *ubufs, GFP_KERNEL);
    if (!ubufs)
        return ERR_PTR(-ENOMEM);
    kref_init(&ubufs->kref);
    init_waitqueue_head(&ubufs->wait);
    ubufs->vq = vq;
    return ubufs;
}

void vhost_ubuf_put(struct vhost_ubuf_ref *ubufs)
{
    kref_put(&ubufs->kref, vhost_zerocopy_done_signal);
}

void vhost_ubuf_put_and_wait(struct vhost_ubuf_ref *ubufs)
{
    kref_put(&ubufs->kref, vhost_zerocopy_done_signal);
    wait_event(ubufs->wait, !atomic_read(&ubufs->kref.refcount));
    kfree(ubufs);
}

void vhost_zerocopy_callback(struct ubuf_info *ubuf)
{
    struct vhost_ubuf_ref *ubufs = ubuf->ctx;
    struct vhost_virtqueue *vq = ubufs->vq;

    vhost_poll_queue(&vq->poll);
    /* set len = 1 to mark this desc buffers done DMA */
    vq->heads[ubuf->desc].len = VHOST_DMA_DONE_LEN;
    kref_put(&ubufs->kref, vhost_zerocopy_done_signal);
}