// SPDX-License-Identifier: GPL-2.0-only
/* Copyright (C) 2009 Red Hat, Inc.
 * Copyright (C) 2006 Rusty Russell IBM Corporation
 *
 * Author: Michael S. Tsirkin <mst@redhat.com>
 *
 * Inspiration, some code, and most witty comments come from
 * Documentation/virtual/lguest/lguest.c, by Rusty Russell
 *
 * Generic code for virtio server in host kernel.
 */

#include <linux/eventfd.h>
#include <linux/vhost.h>
#include <linux/uio.h>
#include <linux/mm.h>
#include <linux/miscdevice.h>
#include <linux/mutex.h>
#include <linux/poll.h>
#include <linux/file.h>
#include <linux/highmem.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/kthread.h>
#include <linux/cgroup.h>
#include <linux/module.h>
#include <linux/sort.h>
#include <linux/sched/mm.h>
#include <linux/sched/signal.h>
#include <linux/interval_tree_generic.h>
#include <linux/nospec.h>
#include <linux/kcov.h>

#include "vhost.h"

static ushort max_mem_regions = 64;
module_param(max_mem_regions, ushort, 0444);
MODULE_PARM_DESC(max_mem_regions,
        "Maximum number of memory regions in memory map. (default: 64)");
static int max_iotlb_entries = 2048;
module_param(max_iotlb_entries, int, 0444);
MODULE_PARM_DESC(max_iotlb_entries,
        "Maximum number of iotlb entries. (default: 2048)");

enum {
        VHOST_MEMORY_F_LOG = 0x1,
};

#define vhost_used_event(vq) ((__virtio16 __user *)&vq->avail->ring[vq->num])
#define vhost_avail_event(vq) ((__virtio16 __user *)&vq->used->ring[vq->num])

#ifdef CONFIG_VHOST_CROSS_ENDIAN_LEGACY
static void vhost_disable_cross_endian(struct vhost_virtqueue *vq)
{
        vq->user_be = !virtio_legacy_is_little_endian();
}

static void vhost_enable_cross_endian_big(struct vhost_virtqueue *vq)
{
        vq->user_be = true;
}

static void vhost_enable_cross_endian_little(struct vhost_virtqueue *vq)
{
        vq->user_be = false;
}

static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp)
{
        struct vhost_vring_state s;

        if (vq->private_data)
                return -EBUSY;

        if (copy_from_user(&s, argp, sizeof(s)))
                return -EFAULT;

        if (s.num != VHOST_VRING_LITTLE_ENDIAN &&
            s.num != VHOST_VRING_BIG_ENDIAN)
                return -EINVAL;

        if (s.num == VHOST_VRING_BIG_ENDIAN)
                vhost_enable_cross_endian_big(vq);
        else
                vhost_enable_cross_endian_little(vq);

        return 0;
}

static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx,
                                   int __user *argp)
{
        struct vhost_vring_state s = {
                .index = idx,
                .num = vq->user_be
        };

        if (copy_to_user(argp, &s, sizeof(s)))
                return -EFAULT;

        return 0;
}

static void vhost_init_is_le(struct vhost_virtqueue *vq)
{
        /* Note for legacy virtio: user_be is initialized at reset time
         * according to the host endianness. If userspace does not set an
         * explicit endianness, the default behavior is native endian, as
         * expected by legacy virtio.
         */
        vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1) || !vq->user_be;
}
#else
static void vhost_disable_cross_endian(struct vhost_virtqueue *vq)
{
}

static long vhost_set_vring_endian(struct vhost_virtqueue *vq, int __user *argp)
{
        return -ENOIOCTLCMD;
}

static long vhost_get_vring_endian(struct vhost_virtqueue *vq, u32 idx,
                                   int __user *argp)
{
        return -ENOIOCTLCMD;
}

static void vhost_init_is_le(struct vhost_virtqueue *vq)
{
        vq->is_le = vhost_has_feature(vq, VIRTIO_F_VERSION_1)
                || virtio_legacy_is_little_endian();
}
#endif /* CONFIG_VHOST_CROSS_ENDIAN_LEGACY */

static void vhost_reset_is_le(struct vhost_virtqueue *vq)
{
        vhost_init_is_le(vq);
}

struct vhost_flush_struct {
        struct vhost_work work;
        struct completion wait_event;
};

static void vhost_flush_work(struct vhost_work *work)
{
        struct vhost_flush_struct *s;

        s = container_of(work, struct vhost_flush_struct, work);
        complete(&s->wait_event);
}

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_entry_t *wait, unsigned mode, int sync,
                             void *key)
{
        struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait);
        struct vhost_work *work = &poll->work;

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

        if (!poll->dev->use_worker)
                work->fn(work);
        else
                vhost_poll_queue(poll);

        return 0;
}

void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
{
        clear_bit(VHOST_WORK_QUEUED, &work->flags);
        work->fn = fn;
}
EXPORT_SYMBOL_GPL(vhost_work_init);

/* Init poll structure */
void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
                     __poll_t 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;
        poll->wqh = NULL;

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

/* 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. */
int vhost_poll_start(struct vhost_poll *poll, struct file *file)
{
        __poll_t mask;

        if (poll->wqh)
                return 0;

        mask = vfs_poll(file, &poll->table);
        if (mask)
                vhost_poll_wakeup(&poll->wait, 0, 0, poll_to_key(mask));
        if (mask & EPOLLERR) {
                vhost_poll_stop(poll);
                return -EINVAL;
        }

        return 0;
}
EXPORT_SYMBOL_GPL(vhost_poll_start);

/* 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)
{
        if (poll->wqh) {
                remove_wait_queue(poll->wqh, &poll->wait);
                poll->wqh = NULL;
        }
}
EXPORT_SYMBOL_GPL(vhost_poll_stop);

void vhost_work_flush(struct vhost_dev *dev, struct vhost_work *work)
{
        struct vhost_flush_struct flush;

        if (dev->worker) {
                init_completion(&flush.wait_event);
                vhost_work_init(&flush.work, vhost_flush_work);

                vhost_work_queue(dev, &flush.work);
                wait_for_completion(&flush.wait_event);
        }
}
EXPORT_SYMBOL_GPL(vhost_work_flush);

/* 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);
}
EXPORT_SYMBOL_GPL(vhost_poll_flush);

void vhost_work_queue(struct vhost_dev *dev, struct vhost_work *work)
{
        if (!dev->worker)
                return;

        if (!test_and_set_bit(VHOST_WORK_QUEUED, &work->flags)) {
                /* We can only add the work to the list after we're
                 * sure it was not in the list.
                 * test_and_set_bit() implies a memory barrier.
                 */
                llist_add(&work->node, &dev->work_list);
                wake_up_process(dev->worker);
        }
}
EXPORT_SYMBOL_GPL(vhost_work_queue);

/* A lockless hint for busy polling code to exit the loop */
bool vhost_has_work(struct vhost_dev *dev)
{
        return !llist_empty(&dev->work_list);
}
EXPORT_SYMBOL_GPL(vhost_has_work);

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

static void __vhost_vq_meta_reset(struct vhost_virtqueue *vq)
{
        int j;

        for (j = 0; j < VHOST_NUM_ADDRS; j++)
                vq->meta_iotlb[j] = NULL;
}

static void vhost_vq_meta_reset(struct vhost_dev *d)
{
        int i;

        for (i = 0; i < d->nvqs; ++i)
                __vhost_vq_meta_reset(d->vqs[i]);
}

static void vhost_vring_call_reset(struct vhost_vring_call *call_ctx)
{
        call_ctx->ctx = NULL;
        memset(&call_ctx->producer, 0x0, sizeof(struct irq_bypass_producer));
}

bool vhost_vq_is_setup(struct vhost_virtqueue *vq)
{
        return vq->avail && vq->desc && vq->used && vhost_vq_access_ok(vq);
}
EXPORT_SYMBOL_GPL(vhost_vq_is_setup);

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->private_data = NULL;
        vq->acked_features = 0;
        vq->acked_backend_features = 0;
        vq->log_base = NULL;
        vq->error_ctx = NULL;
        vq->kick = NULL;
        vq->log_ctx = NULL;
        vhost_disable_cross_endian(vq);
        vhost_reset_is_le(vq);
        vq->busyloop_timeout = 0;
        vq->umem = NULL;
        vq->iotlb = NULL;
        vhost_vring_call_reset(&vq->call_ctx);
        __vhost_vq_meta_reset(vq);
}

static int vhost_worker(void *data)
{
        struct vhost_dev *dev = data;
        struct vhost_work *work, *work_next;
        struct llist_node *node;

        kthread_use_mm(dev->mm);

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

                if (kthread_should_stop()) {
                        __set_current_state(TASK_RUNNING);
                        break;
                }

                node = llist_del_all(&dev->work_list);
                if (!node)
                        schedule();

                node = llist_reverse_order(node);
                /* make sure flag is seen after deletion */
                smp_wmb();
                llist_for_each_entry_safe(work, work_next, node, node) {
                        clear_bit(VHOST_WORK_QUEUED, &work->flags);
                        __set_current_state(TASK_RUNNING);
                        kcov_remote_start_common(dev->kcov_handle);
                        work->fn(work);
                        kcov_remote_stop();
                        if (need_resched())
                                schedule();
                }
        }
        kthread_unuse_mm(dev->mm);
        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;
}

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

        for (i = 0; i < dev->nvqs; ++i) {
                vq = dev->vqs[i];
                vq->indirect = kmalloc_array(UIO_MAXIOV,
                                             sizeof(*vq->indirect),
                                             GFP_KERNEL);
                vq->log = kmalloc_array(dev->iov_limit, sizeof(*vq->log),
                                        GFP_KERNEL);
                vq->heads = kmalloc_array(dev->iov_limit, sizeof(*vq->heads),
                                          GFP_KERNEL);
                if (!vq->indirect || !vq->log || !vq->heads)
                        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]);
}

bool vhost_exceeds_weight(struct vhost_virtqueue *vq,
                          int pkts, int total_len)
{
        struct vhost_dev *dev = vq->dev;

        if ((dev->byte_weight && total_len >= dev->byte_weight) ||
            pkts >= dev->weight) {
                vhost_poll_queue(&vq->poll);
                return true;
        }

        return false;
}
EXPORT_SYMBOL_GPL(vhost_exceeds_weight);

static size_t vhost_get_avail_size(struct vhost_virtqueue *vq,
                                   unsigned int num)
{
        size_t event __maybe_unused =
               vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;

        return sizeof(*vq->avail) +
               sizeof(*vq->avail->ring) * num + event;
}

static size_t vhost_get_used_size(struct vhost_virtqueue *vq,
                                  unsigned int num)
{
        size_t event __maybe_unused =
               vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;

        return sizeof(*vq->used) +
               sizeof(*vq->used->ring) * num + event;
}

static size_t vhost_get_desc_size(struct vhost_virtqueue *vq,
                                  unsigned int num)
{
        return sizeof(*vq->desc) * num;
}

void vhost_dev_init(struct vhost_dev *dev,
                    struct vhost_virtqueue **vqs, int nvqs,
                    int iov_limit, int weight, int byte_weight,
                    bool use_worker,
                    int (*msg_handler)(struct vhost_dev *dev,
                                       struct vhost_iotlb_msg *msg))
{
        struct vhost_virtqueue *vq;
        int i;

        dev->vqs = vqs;
        dev->nvqs = nvqs;
        mutex_init(&dev->mutex);
        dev->log_ctx = NULL;
        dev->umem = NULL;
        dev->iotlb = NULL;
        dev->mm = NULL;
        dev->worker = NULL;
        dev->iov_limit = iov_limit;
        dev->weight = weight;
        dev->byte_weight = byte_weight;
        dev->use_worker = use_worker;
        dev->msg_handler = msg_handler;
        init_llist_head(&dev->work_list);
        init_waitqueue_head(&dev->wait);
        INIT_LIST_HEAD(&dev->read_list);
        INIT_LIST_HEAD(&dev->pending_list);
        spin_lock_init(&dev->iotlb_lock);


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

/* 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;
}
EXPORT_SYMBOL_GPL(vhost_dev_check_owner);

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 */
bool vhost_dev_has_owner(struct vhost_dev *dev)
{
        return dev->mm;
}
EXPORT_SYMBOL_GPL(vhost_dev_has_owner);

static void vhost_attach_mm(struct vhost_dev *dev)
{
        /* No owner, become one */
        if (dev->use_worker) {
                dev->mm = get_task_mm(current);
        } else {
                /* vDPA device does not use worker thead, so there's
                 * no need to hold the address space for mm. This help
                 * to avoid deadlock in the case of mmap() which may
                 * held the refcnt of the file and depends on release
                 * method to remove vma.
                 */
                dev->mm = current->mm;
                mmgrab(dev->mm);
        }
}

static void vhost_detach_mm(struct vhost_dev *dev)
{
        if (!dev->mm)
                return;

        if (dev->use_worker)
                mmput(dev->mm);
        else
                mmdrop(dev->mm);

        dev->mm = NULL;
}

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

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

        vhost_attach_mm(dev);

        dev->kcov_handle = kcov_common_handle();
        if (dev->use_worker) {
                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:
        if (dev->worker) {
                kthread_stop(dev->worker);
                dev->worker = NULL;
        }
err_worker:
        vhost_detach_mm(dev);
        dev->kcov_handle = 0;
err_mm:
        return err;
}
EXPORT_SYMBOL_GPL(vhost_dev_set_owner);

static struct vhost_iotlb *iotlb_alloc(void)
{
        return vhost_iotlb_alloc(max_iotlb_entries,
                                 VHOST_IOTLB_FLAG_RETIRE);
}

struct vhost_iotlb *vhost_dev_reset_owner_prepare(void)
{
        return iotlb_alloc();
}
EXPORT_SYMBOL_GPL(vhost_dev_reset_owner_prepare);

/* Caller should have device mutex */
void vhost_dev_reset_owner(struct vhost_dev *dev, struct vhost_iotlb *umem)
{
        int i;

        vhost_dev_cleanup(dev);

        dev->umem = umem;
        /* We don't need VQ locks below since vhost_dev_cleanup makes sure
         * VQs aren't running.
         */
        for (i = 0; i < dev->nvqs; ++i)
                dev->vqs[i]->umem = umem;
}
EXPORT_SYMBOL_GPL(vhost_dev_reset_owner);

void vhost_dev_stop(struct vhost_dev *dev)
{
        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);
                }
        }
}
EXPORT_SYMBOL_GPL(vhost_dev_stop);

static void vhost_clear_msg(struct vhost_dev *dev)
{
        struct vhost_msg_node *node, *n;

        spin_lock(&dev->iotlb_lock);

        list_for_each_entry_safe(node, n, &dev->read_list, node) {
                list_del(&node->node);
                kfree(node);
        }

        list_for_each_entry_safe(node, n, &dev->pending_list, node) {
                list_del(&node->node);
                kfree(node);
        }

        spin_unlock(&dev->iotlb_lock);
}

void vhost_dev_cleanup(struct vhost_dev *dev)
{
        int i;

        for (i = 0; i < dev->nvqs; ++i) {
                if (dev->vqs[i]->error_ctx)
                        eventfd_ctx_put(dev->vqs[i]->error_ctx);
                if (dev->vqs[i]->kick)
                        fput(dev->vqs[i]->kick);
                if (dev->vqs[i]->call_ctx.ctx)
                        eventfd_ctx_put(dev->vqs[i]->call_ctx.ctx);
                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;
        /* No one will access memory at this point */
        vhost_iotlb_free(dev->umem);
        dev->umem = NULL;
        vhost_iotlb_free(dev->iotlb);
        dev->iotlb = NULL;
        vhost_clear_msg(dev);
        wake_up_interruptible_poll(&dev->wait, EPOLLIN | EPOLLRDNORM);
        WARN_ON(!llist_empty(&dev->work_list));
        if (dev->worker) {
                kthread_stop(dev->worker);
                dev->worker = NULL;
                dev->kcov_handle = 0;
        }
        vhost_detach_mm(dev);
}
EXPORT_SYMBOL_GPL(vhost_dev_cleanup);

static bool 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 false;

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

static bool vhost_overflow(u64 uaddr, u64 size)
{
        /* Make sure 64 bit math will not overflow. */
        return uaddr > ULONG_MAX || size > ULONG_MAX || uaddr > ULONG_MAX - size;
}

/* Caller should have vq mutex and device mutex. */
static bool vq_memory_access_ok(void __user *log_base, struct vhost_iotlb *umem,
                                int log_all)
{
        struct vhost_iotlb_map *map;

        if (!umem)
                return false;

        list_for_each_entry(map, &umem->list, link) {
                unsigned long a = map->addr;

                if (vhost_overflow(map->addr, map->size))
                        return false;


                if (!access_ok((void __user *)a, map->size))
                        return false;
                else if (log_all && !log_access_ok(log_base,
                                                   map->start,
                                                   map->size))
                        return false;
        }
        return true;
}

static inline void __user *vhost_vq_meta_fetch(struct vhost_virtqueue *vq,
                                               u64 addr, unsigned int size,
                                               int type)
{
        const struct vhost_iotlb_map *map = vq->meta_iotlb[type];

        if (!map)
                return NULL;

        return (void __user *)(uintptr_t)(map->addr + addr - map->start);
}

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

        for (i = 0; i < d->nvqs; ++i) {
                bool ok;
                bool log;

                mutex_lock(&d->vqs[i]->mutex);
                log = log_all || vhost_has_feature(d->vqs[i], VHOST_F_LOG_ALL);
                /* 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,
                                                 umem, log);
                else
                        ok = true;
                mutex_unlock(&d->vqs[i]->mutex);
                if (!ok)
                        return false;
        }
        return true;
}

static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
                          struct iovec iov[], int iov_size, int access);

static int vhost_copy_to_user(struct vhost_virtqueue *vq, void __user *to,
                              const void *from, unsigned size)
{
        int ret;

        if (!vq->iotlb)
                return __copy_to_user(to, from, size);
        else {
                /* This function should be called after iotlb
                 * prefetch, which means we're sure that all vq
                 * could be access through iotlb. So -EAGAIN should
                 * not happen in this case.
                 */
                struct iov_iter t;
                void __user *uaddr = vhost_vq_meta_fetch(vq,
                                     (u64)(uintptr_t)to, size,
                                     VHOST_ADDR_USED);

                if (uaddr)
                        return __copy_to_user(uaddr, from, size);

                ret = translate_desc(vq, (u64)(uintptr_t)to, size, vq->iotlb_iov,
                                     ARRAY_SIZE(vq->iotlb_iov),
                                     VHOST_ACCESS_WO);
                if (ret < 0)
                        goto out;
                iov_iter_init(&t, WRITE, vq->iotlb_iov, ret, size);
                ret = copy_to_iter(from, size, &t);
                if (ret == size)
                        ret = 0;
        }
out:
        return ret;
}

static int vhost_copy_from_user(struct vhost_virtqueue *vq, void *to,
                                void __user *from, unsigned size)
{
        int ret;

        if (!vq->iotlb)
                return __copy_from_user(to, from, size);
        else {
                /* This function should be called after iotlb
                 * prefetch, which means we're sure that vq
                 * could be access through iotlb. So -EAGAIN should
                 * not happen in this case.
                 */
                void __user *uaddr = vhost_vq_meta_fetch(vq,
                                     (u64)(uintptr_t)from, size,
                                     VHOST_ADDR_DESC);
                struct iov_iter f;

                if (uaddr)
                        return __copy_from_user(to, uaddr, size);

                ret = translate_desc(vq, (u64)(uintptr_t)from, size, vq->iotlb_iov,
                                     ARRAY_SIZE(vq->iotlb_iov),
                                     VHOST_ACCESS_RO);
                if (ret < 0) {
                        vq_err(vq, "IOTLB translation failure: uaddr "
                               "%p size 0x%llx\n", from,
                               (unsigned long long) size);
                        goto out;
                }
                iov_iter_init(&f, READ, vq->iotlb_iov, ret, size);
                ret = copy_from_iter(to, size, &f);
                if (ret == size)
                        ret = 0;
        }

out:
        return ret;
}

static void __user *__vhost_get_user_slow(struct vhost_virtqueue *vq,
                                          void __user *addr, unsigned int size,
                                          int type)
{
        int ret;

        ret = translate_desc(vq, (u64)(uintptr_t)addr, size, vq->iotlb_iov,
                             ARRAY_SIZE(vq->iotlb_iov),
                             VHOST_ACCESS_RO);
        if (ret < 0) {
                vq_err(vq, "IOTLB translation failure: uaddr "
                        "%p size 0x%llx\n", addr,
                        (unsigned long long) size);
                return NULL;
        }

        if (ret != 1 || vq->iotlb_iov[0].iov_len != size) {
                vq_err(vq, "Non atomic userspace memory access: uaddr "
                        "%p size 0x%llx\n", addr,
                        (unsigned long long) size);
                return NULL;
        }

        return vq->iotlb_iov[0].iov_base;
}

/* This function should be called after iotlb
 * prefetch, which means we're sure that vq
 * could be access through iotlb. So -EAGAIN should
 * not happen in this case.
 */
static inline void __user *__vhost_get_user(struct vhost_virtqueue *vq,
                                            void __user *addr, unsigned int size,
                                            int type)
{
        void __user *uaddr = vhost_vq_meta_fetch(vq,
                             (u64)(uintptr_t)addr, size, type);
        if (uaddr)
                return uaddr;

        return __vhost_get_user_slow(vq, addr, size, type);
}

#define vhost_put_user(vq, x, ptr)              \
({ \
        int ret; \
        if (!vq->iotlb) { \
                ret = __put_user(x, ptr); \
        } else { \
                __typeof__(ptr) to = \
                        (__typeof__(ptr)) __vhost_get_user(vq, ptr,     \
                                          sizeof(*ptr), VHOST_ADDR_USED); \
                if (to != NULL) \
                        ret = __put_user(x, to); \
                else \
                        ret = -EFAULT;  \
        } \
        ret; \
})

static inline int vhost_put_avail_event(struct vhost_virtqueue *vq)
{
        return vhost_put_user(vq, cpu_to_vhost16(vq, vq->avail_idx),
                              vhost_avail_event(vq));
}

static inline int vhost_put_used(struct vhost_virtqueue *vq,
                                 struct vring_used_elem *head, int idx,
                                 int count)
{
        return vhost_copy_to_user(vq, vq->used->ring + idx, head,
                                  count * sizeof(*head));
}

static inline int vhost_put_used_flags(struct vhost_virtqueue *vq)

{
        return vhost_put_user(vq, cpu_to_vhost16(vq, vq->used_flags),
                              &vq->used->flags);
}

static inline int vhost_put_used_idx(struct vhost_virtqueue *vq)

{
        return vhost_put_user(vq, cpu_to_vhost16(vq, vq->last_used_idx),
                              &vq->used->idx);
}

#define vhost_get_user(vq, x, ptr, type)                \
({ \
        int ret; \
        if (!vq->iotlb) { \
                ret = __get_user(x, ptr); \
        } else { \
                __typeof__(ptr) from = \
                        (__typeof__(ptr)) __vhost_get_user(vq, ptr, \
                                                           sizeof(*ptr), \
                                                           type); \
                if (from != NULL) \
                        ret = __get_user(x, from); \
                else \
                        ret = -EFAULT; \
        } \
        ret; \
})

#define vhost_get_avail(vq, x, ptr) \
        vhost_get_user(vq, x, ptr, VHOST_ADDR_AVAIL)

#define vhost_get_used(vq, x, ptr) \
        vhost_get_user(vq, x, ptr, VHOST_ADDR_USED)

static void vhost_dev_lock_vqs(struct vhost_dev *d)
{
        int i = 0;

        for (i = 0; i < d->nvqs; ++i)
                mutex_lock_nested(&d->vqs[i]->mutex, i);
}

static void vhost_dev_unlock_vqs(struct vhost_dev *d)
{
        int i = 0;
        for (i = 0; i < d->nvqs; ++i)
                mutex_unlock(&d->vqs[i]->mutex);
}

static inline int vhost_get_avail_idx(struct vhost_virtqueue *vq,
                                      __virtio16 *idx)
{
        return vhost_get_avail(vq, *idx, &vq->avail->idx);
}

static inline int vhost_get_avail_head(struct vhost_virtqueue *vq,
                                       __virtio16 *head, int idx)
{
        return vhost_get_avail(vq, *head,
                               &vq->avail->ring[idx & (vq->num - 1)]);
}

static inline int vhost_get_avail_flags(struct vhost_virtqueue *vq,
                                        __virtio16 *flags)
{
        return vhost_get_avail(vq, *flags, &vq->avail->flags);
}

static inline int vhost_get_used_event(struct vhost_virtqueue *vq,
                                       __virtio16 *event)
{
        return vhost_get_avail(vq, *event, vhost_used_event(vq));
}

static inline int vhost_get_used_idx(struct vhost_virtqueue *vq,
                                     __virtio16 *idx)
{
        return vhost_get_used(vq, *idx, &vq->used->idx);
}

static inline int vhost_get_desc(struct vhost_virtqueue *vq,
                                 struct vring_desc *desc, int idx)
{
        return vhost_copy_from_user(vq, desc, vq->desc + idx, sizeof(*desc));
}

static void vhost_iotlb_notify_vq(struct vhost_dev *d,
                                  struct vhost_iotlb_msg *msg)
{
        struct vhost_msg_node *node, *n;

        spin_lock(&d->iotlb_lock);

        list_for_each_entry_safe(node, n, &d->pending_list, node) {
                struct vhost_iotlb_msg *vq_msg = &node->msg.iotlb;
                if (msg->iova <= vq_msg->iova &&
                    msg->iova + msg->size - 1 >= vq_msg->iova &&
                    vq_msg->type == VHOST_IOTLB_MISS) {
                        vhost_poll_queue(&node->vq->poll);
                        list_del(&node->node);
                        kfree(node);
                }
        }

        spin_unlock(&d->iotlb_lock);
}

static bool umem_access_ok(u64 uaddr, u64 size, int access)
{
        unsigned long a = uaddr;

        /* Make sure 64 bit math will not overflow. */
        if (vhost_overflow(uaddr, size))
                return false;

        if ((access & VHOST_ACCESS_RO) &&
            !access_ok((void __user *)a, size))
                return false;
        if ((access & VHOST_ACCESS_WO) &&
            !access_ok((void __user *)a, size))
                return false;
        return true;
}

static int vhost_process_iotlb_msg(struct vhost_dev *dev,
                                   struct vhost_iotlb_msg *msg)
{
        int ret = 0;

        mutex_lock(&dev->mutex);
        vhost_dev_lock_vqs(dev);
        switch (msg->type) {
        case VHOST_IOTLB_UPDATE:
                if (!dev->iotlb) {
                        ret = -EFAULT;
                        break;
                }
                if (!umem_access_ok(msg->uaddr, msg->size, msg->perm)) {
                        ret = -EFAULT;
                        break;
                }
                vhost_vq_meta_reset(dev);
                if (vhost_iotlb_add_range(dev->iotlb, msg->iova,
                                          msg->iova + msg->size - 1,
                                          msg->uaddr, msg->perm)) {
                        ret = -ENOMEM;
                        break;
                }
                vhost_iotlb_notify_vq(dev, msg);
                break;
        case VHOST_IOTLB_INVALIDATE:
                if (!dev->iotlb) {
                        ret = -EFAULT;
                        break;
                }
                vhost_vq_meta_reset(dev);
                vhost_iotlb_del_range(dev->iotlb, msg->iova,
                                      msg->iova + msg->size - 1);
                break;
        default:
                ret = -EINVAL;
                break;
        }

        vhost_dev_unlock_vqs(dev);
        mutex_unlock(&dev->mutex);

        return ret;
}
ssize_t vhost_chr_write_iter(struct vhost_dev *dev,
                             struct iov_iter *from)
{
        struct vhost_iotlb_msg msg;
        size_t offset;
        int type, ret;

        ret = copy_from_iter(&type, sizeof(type), from);
        if (ret != sizeof(type)) {
                ret = -EINVAL;
                goto done;
        }

        switch (type) {
        case VHOST_IOTLB_MSG:
                /* There maybe a hole after type for V1 message type,
                 * so skip it here.
                 */
                offset = offsetof(struct vhost_msg, iotlb) - sizeof(int);
                break;
        case VHOST_IOTLB_MSG_V2:
                offset = sizeof(__u32);
                break;
        default:
                ret = -EINVAL;
                goto done;
        }

        iov_iter_advance(from, offset);
        ret = copy_from_iter(&msg, sizeof(msg), from);
        if (ret != sizeof(msg)) {
                ret = -EINVAL;
                goto done;
        }

        if (dev->msg_handler)
                ret = dev->msg_handler(dev, &msg);
        else
                ret = vhost_process_iotlb_msg(dev, &msg);
        if (ret) {
                ret = -EFAULT;
                goto done;
        }

        ret = (type == VHOST_IOTLB_MSG) ? sizeof(struct vhost_msg) :
              sizeof(struct vhost_msg_v2);
done:
        return ret;
}
EXPORT_SYMBOL(vhost_chr_write_iter);

__poll_t vhost_chr_poll(struct file *file, struct vhost_dev *dev,
                            poll_table *wait)
{
        __poll_t mask = 0;

        poll_wait(file, &dev->wait, wait);

        if (!list_empty(&dev->read_list))
                mask |= EPOLLIN | EPOLLRDNORM;

        return mask;
}
EXPORT_SYMBOL(vhost_chr_poll);

ssize_t vhost_chr_read_iter(struct vhost_dev *dev, struct iov_iter *to,
                            int noblock)
{
        DEFINE_WAIT(wait);
        struct vhost_msg_node *node;
        ssize_t ret = 0;
        unsigned size = sizeof(struct vhost_msg);

        if (iov_iter_count(to) < size)
                return 0;

        while (1) {
                if (!noblock)
                        prepare_to_wait(&dev->wait, &wait,
                                        TASK_INTERRUPTIBLE);

                node = vhost_dequeue_msg(dev, &dev->read_list);
                if (node)
                        break;
                if (noblock) {
                        ret = -EAGAIN;
                        break;
                }
                if (signal_pending(current)) {
                        ret = -ERESTARTSYS;
                        break;
                }
                if (!dev->iotlb) {
                        ret = -EBADFD;
                        break;
                }

                schedule();
        }

        if (!noblock)
                finish_wait(&dev->wait, &wait);

        if (node) {
                struct vhost_iotlb_msg *msg;
                void *start = &node->msg;

                switch (node->msg.type) {
                case VHOST_IOTLB_MSG:
                        size = sizeof(node->msg);
                        msg = &node->msg.iotlb;
                        break;
                case VHOST_IOTLB_MSG_V2:
                        size = sizeof(node->msg_v2);
                        msg = &node->msg_v2.iotlb;
                        break;
                default:
                        BUG();
                        break;
                }

                ret = copy_to_iter(start, size, to);
                if (ret != size || msg->type != VHOST_IOTLB_MISS) {
                        kfree(node);
                        return ret;
                }
                vhost_enqueue_msg(dev, &dev->pending_list, node);
        }

        return ret;
}
EXPORT_SYMBOL_GPL(vhost_chr_read_iter);

static int vhost_iotlb_miss(struct vhost_virtqueue *vq, u64 iova, int access)
{
        struct vhost_dev *dev = vq->dev;
        struct vhost_msg_node *node;
        struct vhost_iotlb_msg *msg;
        bool v2 = vhost_backend_has_feature(vq, VHOST_BACKEND_F_IOTLB_MSG_V2);

        node = vhost_new_msg(vq, v2 ? VHOST_IOTLB_MSG_V2 : VHOST_IOTLB_MSG);
        if (!node)
                return -ENOMEM;

        if (v2) {
                node->msg_v2.type = VHOST_IOTLB_MSG_V2;
                msg = &node->msg_v2.iotlb;
        } else {
                msg = &node->msg.iotlb;
        }

        msg->type = VHOST_IOTLB_MISS;
        msg->iova = iova;
        msg->perm = access;

        vhost_enqueue_msg(dev, &dev->read_list, node);

        return 0;
}

static bool vq_access_ok(struct vhost_virtqueue *vq, unsigned int num,
                         vring_desc_t __user *desc,
                         vring_avail_t __user *avail,
                         vring_used_t __user *used)

{
        /* If an IOTLB device is present, the vring addresses are
         * GIOVAs. Access validation occurs at prefetch time. */
        if (vq->iotlb)
                return true;

        return access_ok(desc, vhost_get_desc_size(vq, num)) &&
               access_ok(avail, vhost_get_avail_size(vq, num)) &&
               access_ok(used, vhost_get_used_size(vq, num));
}

static void vhost_vq_meta_update(struct vhost_virtqueue *vq,
                                 const struct vhost_iotlb_map *map,
                                 int type)
{
        int access = (type == VHOST_ADDR_USED) ?
                     VHOST_ACCESS_WO : VHOST_ACCESS_RO;

        if (likely(map->perm & access))
                vq->meta_iotlb[type] = map;
}

static bool iotlb_access_ok(struct vhost_virtqueue *vq,
                            int access, u64 addr, u64 len, int type)
{
        const struct vhost_iotlb_map *map;
        struct vhost_iotlb *umem = vq->iotlb;
        u64 s = 0, size, orig_addr = addr, last = addr + len - 1;

        if (vhost_vq_meta_fetch(vq, addr, len, type))
                return true;

        while (len > s) {
                map = vhost_iotlb_itree_first(umem, addr, last);
                if (map == NULL || map->start > addr) {
                        vhost_iotlb_miss(vq, addr, access);
                        return false;
                } else if (!(map->perm & access)) {
                        /* Report the possible access violation by
                         * request another translation from userspace.
                         */
                        return false;
                }

                size = map->size - addr + map->start;

                if (orig_addr == addr && size >= len)
                        vhost_vq_meta_update(vq, map, type);

                s += size;
                addr += size;
        }

        return true;
}

int vq_meta_prefetch(struct vhost_virtqueue *vq)
{
        unsigned int num = vq->num;

        if (!vq->iotlb)
                return 1;

        return iotlb_access_ok(vq, VHOST_MAP_RO, (u64)(uintptr_t)vq->desc,
                               vhost_get_desc_size(vq, num), VHOST_ADDR_DESC) &&
               iotlb_access_ok(vq, VHOST_MAP_RO, (u64)(uintptr_t)vq->avail,
                               vhost_get_avail_size(vq, num),
                               VHOST_ADDR_AVAIL) &&
               iotlb_access_ok(vq, VHOST_MAP_WO, (u64)(uintptr_t)vq->used,
                               vhost_get_used_size(vq, num), VHOST_ADDR_USED);
}
EXPORT_SYMBOL_GPL(vq_meta_prefetch);

/* Can we log writes? */
/* Caller should have device mutex but not vq mutex */
bool vhost_log_access_ok(struct vhost_dev *dev)
{
        return memory_access_ok(dev, dev->umem, 1);
}
EXPORT_SYMBOL_GPL(vhost_log_access_ok);

static bool vq_log_used_access_ok(struct vhost_virtqueue *vq,
                                  void __user *log_base,
                                  bool log_used,
                                  u64 log_addr)
{
        /* If an IOTLB device is present, log_addr is a GIOVA that
         * will never be logged by log_used(). */
        if (vq->iotlb)
                return true;

        return !log_used || log_access_ok(log_base, log_addr,
                                          vhost_get_used_size(vq, vq->num));
}

/* Verify access for write logging. */
/* Caller should have vq mutex and device mutex */
static bool vq_log_access_ok(struct vhost_virtqueue *vq,
                             void __user *log_base)
{
        return vq_memory_access_ok(log_base, vq->umem,
                                   vhost_has_feature(vq, VHOST_F_LOG_ALL)) &&
                vq_log_used_access_ok(vq, log_base, vq->log_used, vq->log_addr);
}

/* Can we start vq? */
/* Caller should have vq mutex and device mutex */
bool vhost_vq_access_ok(struct vhost_virtqueue *vq)
{
        if (!vq_log_access_ok(vq, vq->log_base))
                return false;

        return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used);
}
EXPORT_SYMBOL_GPL(vhost_vq_access_ok);

static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
{
        struct vhost_memory mem, *newmem;
        struct vhost_memory_region *region;
        struct vhost_iotlb *newumem, *oldumem;
        unsigned long size = offsetof(struct vhost_memory, regions);
        int i;

        if (copy_from_user(&mem, m, size))
                return -EFAULT;
        if (mem.padding)
                return -EOPNOTSUPP;
        if (mem.nregions > max_mem_regions)
                return -E2BIG;
        newmem = kvzalloc(struct_size(newmem, regions, mem.nregions),
                        GFP_KERNEL);
        if (!newmem)
                return -ENOMEM;

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

        newumem = iotlb_alloc();
        if (!newumem) {
                kvfree(newmem);
                return -ENOMEM;
        }

        for (region = newmem->regions;
             region < newmem->regions + mem.nregions;
             region++) {
                if (vhost_iotlb_add_range(newumem,
                                          region->guest_phys_addr,
                                          region->guest_phys_addr +
                                          region->memory_size - 1,
                                          region->userspace_addr,
                                          VHOST_MAP_RW))
                        goto err;
        }

        if (!memory_access_ok(d, newumem, 0))
                goto err;

        oldumem = d->umem;
        d->umem = newumem;

        /* All memory accesses are done under some VQ mutex. */
        for (i = 0; i < d->nvqs; ++i) {
                mutex_lock(&d->vqs[i]->mutex);
                d->vqs[i]->umem = newumem;
                mutex_unlock(&d->vqs[i]->mutex);
        }

        kvfree(newmem);
        vhost_iotlb_free(oldumem);
        return 0;

err:
        vhost_iotlb_free(newumem);
        kvfree(newmem);
        return -EFAULT;
}

static long vhost_vring_set_num(struct vhost_dev *d,
                                struct vhost_virtqueue *vq,
                                void __user *argp)
{
        struct vhost_vring_state s;

        /* Resizing ring with an active backend?
         * You don't want to do that. */
        if (vq->private_data)
                return -EBUSY;

        if (copy_from_user(&s, argp, sizeof s))
                return -EFAULT;

        if (!s.num || s.num > 0xffff || (s.num & (s.num - 1)))
                return -EINVAL;
        vq->num = s.num;

        return 0;
}

static long vhost_vring_set_addr(struct vhost_dev *d,
                                 struct vhost_virtqueue *vq,
                                 void __user *argp)
{
        struct vhost_vring_addr a;

        if (copy_from_user(&a, argp, sizeof a))
                return -EFAULT;
        if (a.flags & ~(0x1 << VHOST_VRING_F_LOG))
                return -EOPNOTSUPP;

        /* 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)
                return -EFAULT;

        /* Make sure it's safe to cast pointers to vring types. */
        BUILD_BUG_ON(__alignof__ *vq->avail > VRING_AVAIL_ALIGN_SIZE);
        BUILD_BUG_ON(__alignof__ *vq->used > VRING_USED_ALIGN_SIZE);
        if ((a.avail_user_addr & (VRING_AVAIL_ALIGN_SIZE - 1)) ||
            (a.used_user_addr & (VRING_USED_ALIGN_SIZE - 1)) ||
            (a.log_guest_addr & (VRING_USED_ALIGN_SIZE - 1)))
                return -EINVAL;

        /* 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(vq, 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))
                        return -EINVAL;

                /* Also validate log access for used ring if enabled. */
                if (!vq_log_used_access_ok(vq, vq->log_base,
                                a.flags & (0x1 << VHOST_VRING_F_LOG),
                                a.log_guest_addr))
                        return -EINVAL;
        }

        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;

        return 0;
}

static long vhost_vring_set_num_addr(struct vhost_dev *d,
                                     struct vhost_virtqueue *vq,
                                     unsigned int ioctl,
                                     void __user *argp)
{
        long r;

        mutex_lock(&vq->mutex);

        switch (ioctl) {
        case VHOST_SET_VRING_NUM:
                r = vhost_vring_set_num(d, vq, argp);
                break;
        case VHOST_SET_VRING_ADDR:
                r = vhost_vring_set_addr(d, vq, argp);
                break;
        default:
                BUG();
        }

        mutex_unlock(&vq->mutex);

        return r;
}
long vhost_vring_ioctl(struct vhost_dev *d, unsigned 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;
        u32 idx;
        long r;

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

        idx = array_index_nospec(idx, d->nvqs);
        vq = d->vqs[idx];

        if (ioctl == VHOST_SET_VRING_NUM ||
            ioctl == VHOST_SET_VRING_ADDR) {
                return vhost_vring_set_num_addr(d, vq, ioctl, argp);
        }

        mutex_lock(&vq->mutex);

        switch (ioctl) {
        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_KICK:
                if (copy_from_user(&f, argp, sizeof f)) {
                        r = -EFAULT;
                        break;
                }
                eventfp = f.fd == VHOST_FILE_UNBIND ? 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;
                }
                ctx = f.fd == VHOST_FILE_UNBIND ? NULL : eventfd_ctx_fdget(f.fd);
                if (IS_ERR(ctx)) {
                        r = PTR_ERR(ctx);
                        break;
                }

                swap(ctx, vq->call_ctx.ctx);
                break;
        case VHOST_SET_VRING_ERR:
                if (copy_from_user(&f, argp, sizeof f)) {
                        r = -EFAULT;
                        break;
                }
                ctx = f.fd == VHOST_FILE_UNBIND ? NULL : eventfd_ctx_fdget(f.fd);
                if (IS_ERR(ctx)) {
                        r = PTR_ERR(ctx);
                        break;
                }
                swap(ctx, vq->error_ctx);
                break;
        case VHOST_SET_VRING_ENDIAN:
                r = vhost_set_vring_endian(vq, argp);
                break;
        case VHOST_GET_VRING_ENDIAN:
                r = vhost_get_vring_endian(vq, idx, argp);
                break;
        case VHOST_SET_VRING_BUSYLOOP_TIMEOUT:
                if (copy_from_user(&s, argp, sizeof(s))) {
                        r = -EFAULT;
                        break;
                }
                vq->busyloop_timeout = s.num;
                break;
        case VHOST_GET_VRING_BUSYLOOP_TIMEOUT:
                s.index = idx;
                s.num = vq->busyloop_timeout;
                if (copy_to_user(argp, &s, sizeof(s)))
                        r = -EFAULT;
                break;
        default:
                r = -ENOIOCTLCMD;
        }

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

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

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

        mutex_unlock(&vq->mutex);

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

int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
{
        struct vhost_iotlb *niotlb, *oiotlb;
        int i;

        niotlb = iotlb_alloc();
        if (!niotlb)
                return -ENOMEM;

        oiotlb = d->iotlb;
        d->iotlb = niotlb;

        for (i = 0; i < d->nvqs; ++i) {
                struct vhost_virtqueue *vq = d->vqs[i];

                mutex_lock(&vq->mutex);
                vq->iotlb = niotlb;
                __vhost_vq_meta_reset(vq);
                mutex_unlock(&vq->mutex);
        }

        vhost_iotlb_free(oiotlb);

        return 0;
}
EXPORT_SYMBOL_GPL(vhost_init_device_iotlb);

/* Caller must have device mutex */
long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
{
        struct eventfd_ctx *ctx;
        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(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;
                ctx = fd == VHOST_FILE_UNBIND ? NULL : eventfd_ctx_fdget(fd);
                if (IS_ERR(ctx)) {
                        r = PTR_ERR(ctx);
                        break;
                }
                swap(ctx, d->log_ctx);
                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);
                break;
        default:
                r = -ENOIOCTLCMD;
                break;
        }
done:
        return r;
}
EXPORT_SYMBOL_GPL(vhost_dev_ioctl);

/* 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.rst.
 */
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 = pin_user_pages_fast(log, 1, FOLL_WRITE, &page);
        if (r < 0)
                return r;
        BUG_ON(r != 1);
        base = kmap_atomic(page);
        set_bit(bit, base);
        kunmap_atomic(base);
        unpin_user_pages_dirty_lock(&page, 1, true);
        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;
}

static int log_write_hva(struct vhost_virtqueue *vq, u64 hva, u64 len)
{
        struct vhost_iotlb *umem = vq->umem;
        struct vhost_iotlb_map *u;
        u64 start, end, l, min;
        int r;
        bool hit = false;

        while (len) {
                min = len;
                /* More than one GPAs can be mapped into a single HVA. So
                 * iterate all possible umems here to be safe.
                 */
                list_for_each_entry(u, &umem->list, link) {
                        if (u->addr > hva - 1 + len ||
                            u->addr - 1 + u->size < hva)
                                continue;
                        start = max(u->addr, hva);
                        end = min(u->addr - 1 + u->size, hva - 1 + len);
                        l = end - start + 1;
                        r = log_write(vq->log_base,
                                      u->start + start - u->addr,
                                      l);
                        if (r < 0)
                                return r;
                        hit = true;
                        min = min(l, min);
                }

                if (!hit)
                        return -EFAULT;

                len -= min;
                hva += min;
        }

        return 0;
}

static int log_used(struct vhost_virtqueue *vq, u64 used_offset, u64 len)
{
        struct iovec *iov = vq->log_iov;
        int i, ret;

        if (!vq->iotlb)
                return log_write(vq->log_base, vq->log_addr + used_offset, len);

        ret = translate_desc(vq, (uintptr_t)vq->used + used_offset,
                             len, iov, 64, VHOST_ACCESS_WO);
        if (ret < 0)
                return ret;

        for (i = 0; i < ret; i++) {
                ret = log_write_hva(vq, (uintptr_t)iov[i].iov_base,
                                    iov[i].iov_len);
                if (ret)
                        return ret;
        }

        return 0;
}

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

        /* Make sure data written is seen before log. */
        smp_wmb();

        if (vq->iotlb) {
                for (i = 0; i < count; i++) {
                        r = log_write_hva(vq, (uintptr_t)iov[i].iov_base,
                                          iov[i].iov_len);
                        if (r < 0)
                                return r;
                }
                return 0;
        }

        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;
}
EXPORT_SYMBOL_GPL(vhost_log_write);

static int vhost_update_used_flags(struct vhost_virtqueue *vq)
{
        void __user *used;
        if (vhost_put_used_flags(vq))
                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_used(vq, (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 (vhost_put_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_used(vq, (used - (void __user *)vq->used),
                         sizeof *vhost_avail_event(vq));
                if (vq->log_ctx)
                        eventfd_signal(vq->log_ctx, 1);
        }
        return 0;
}

int vhost_vq_init_access(struct vhost_virtqueue *vq)
{
        __virtio16 last_used_idx;
        int r;
        bool is_le = vq->is_le;

        if (!vq->private_data)
                return 0;

        vhost_init_is_le(vq);

        r = vhost_update_used_flags(vq);
        if (r)
                goto err;
        vq->signalled_used_valid = false;
        if (!vq->iotlb &&
            !access_ok(&vq->used->idx, sizeof vq->used->idx)) {
                r = -EFAULT;
                goto err;
        }
        r = vhost_get_used_idx(vq, &last_used_idx);
        if (r) {
                vq_err(vq, "Can't access used idx at %p\n",
                       &vq->used->idx);
                goto err;
        }
        vq->last_used_idx = vhost16_to_cpu(vq, last_used_idx);
        return 0;

err:
        vq->is_le = is_le;
        return r;
}
EXPORT_SYMBOL_GPL(vhost_vq_init_access);

static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
                          struct iovec iov[], int iov_size, int access)
{
        const struct vhost_iotlb_map *map;
        struct vhost_dev *dev = vq->dev;
        struct vhost_iotlb *umem = dev->iotlb ? dev->iotlb : dev->umem;
        struct iovec *_iov;
        u64 s = 0;
        int ret = 0;

        while ((u64)len > s) {
                u64 size;
                if (unlikely(ret >= iov_size)) {
                        ret = -ENOBUFS;
                        break;
                }

                map = vhost_iotlb_itree_first(umem, addr, addr + len - 1);
                if (map == NULL || map->start > addr) {
                        if (umem != dev->iotlb) {
                                ret = -EFAULT;
                                break;
                        }
                        ret = -EAGAIN;
                        break;
                } else if (!(map->perm & access)) {
                        ret = -EPERM;
                        break;
                }

                _iov = iov + ret;
                size = map->size - addr + map->start;
                _iov->iov_len = min((u64)len - s, size);
                _iov->iov_base = (void __user *)(unsigned long)
                                 (map->addr + addr - map->start);
                s += size;
                addr += size;
                ++ret;
        }

        if (ret == -EAGAIN)
                vhost_iotlb_miss(vq, addr, access);
        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 vhost_virtqueue *vq, struct vring_desc *desc)
{
        unsigned int next;

        /* If this descriptor says it doesn't chain, we're done. */
        if (!(desc->flags & cpu_to_vhost16(vq, VRING_DESC_F_NEXT)))
                return -1U;

        /* Check they're not leading us off end of descriptors. */
        next = vhost16_to_cpu(vq, READ_ONCE(desc->next));
        return next;
}

static int get_indirect(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;
        u32 len = vhost32_to_cpu(vq, indirect->len);
        struct iov_iter from;
        int ret, access;

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

        ret = translate_desc(vq, vhost64_to_cpu(vq, indirect->addr), len, vq->indirect,
                             UIO_MAXIOV, VHOST_ACCESS_RO);
        if (unlikely(ret < 0)) {
                if (ret != -EAGAIN)
                        vq_err(vq, "Translation failure %d in indirect.\n", ret);
                return ret;
        }
        iov_iter_init(&from, READ, vq->indirect, ret, len);
        count = 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(!copy_from_iter_full(&desc, sizeof(desc), &from))) {
                        vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
                               i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc);
                        return -EINVAL;
                }
                if (unlikely(desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT))) {
                        vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
                               i, (size_t)vhost64_to_cpu(vq, indirect->addr) + i * sizeof desc);
                        return -EINVAL;
                }

                if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
                        access = VHOST_ACCESS_WO;
                else
                        access = VHOST_ACCESS_RO;

                ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
                                     vhost32_to_cpu(vq, desc.len), iov + iov_count,
                                     iov_size - iov_count, access);
                if (unlikely(ret < 0)) {
                        if (ret != -EAGAIN)
                                vq_err(vq, "Translation failure %d indirect idx %d\n",
                                        ret, i);
                        return ret;
                }
                /* If this is an input descriptor, increment that count. */
                if (access == VHOST_ACCESS_WO) {
                        *in_num += ret;
                        if (unlikely(log && ret)) {
                                log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
                                log[*log_num].len = vhost32_to_cpu(vq, 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(vq, &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_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;
        __virtio16 avail_idx;
        __virtio16 ring_head;
        int ret, access;

        /* Check it isn't doing very strange things with descriptor numbers. */
        last_avail_idx = vq->last_avail_idx;

        if (vq->avail_idx == vq->last_avail_idx) {
                if (unlikely(vhost_get_avail_idx(vq, &avail_idx))) {
                        vq_err(vq, "Failed to access avail idx at %p\n",
                                &vq->avail->idx);
                        return -EFAULT;
                }
                vq->avail_idx = vhost16_to_cpu(vq, avail_idx);

                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(vhost_get_avail_head(vq, &ring_head, last_avail_idx))) {
                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;
        }

        head = vhost16_to_cpu(vq, ring_head);

        /* 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 = vhost_get_desc(vq, &desc, i);
                if (unlikely(ret)) {
                        vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
                               i, vq->desc + i);
                        return -EFAULT;
                }
                if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_INDIRECT)) {
                        ret = get_indirect(vq, iov, iov_size,
                                           out_num, in_num,
                                           log, log_num, &desc);
                        if (unlikely(ret < 0)) {
                                if (ret != -EAGAIN)
                                        vq_err(vq, "Failure detected "
                                                "in indirect descriptor at idx %d\n", i);
                                return ret;
                        }
                        continue;
                }

                if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE))
                        access = VHOST_ACCESS_WO;
                else
                        access = VHOST_ACCESS_RO;
                ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
                                     vhost32_to_cpu(vq, desc.len), iov + iov_count,
                                     iov_size - iov_count, access);
                if (unlikely(ret < 0)) {
                        if (ret != -EAGAIN)
                                vq_err(vq, "Translation failure %d descriptor idx %d\n",
                                        ret, i);
                        return ret;
                }
                if (access == VHOST_ACCESS_WO) {
                        /* If this is an input descriptor,
                         * increment that count. */
                        *in_num += ret;
                        if (unlikely(log && ret)) {
                                log[*log_num].addr = vhost64_to_cpu(vq, desc.addr);
                                log[*log_num].len = vhost32_to_cpu(vq, 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(vq, &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;
}
EXPORT_SYMBOL_GPL(vhost_get_vq_desc);

/* 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;
}
EXPORT_SYMBOL_GPL(vhost_discard_vq_desc);

/* 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 heads = {
                cpu_to_vhost32(vq, head),
                cpu_to_vhost32(vq, len)
        };

        return vhost_add_used_n(vq, &heads, 1);
}
EXPORT_SYMBOL_GPL(vhost_add_used);

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

        start = vq->last_used_idx & (vq->num - 1);
        used = vq->used->ring + start;
        if (vhost_put_used(vq, heads, start, count)) {
                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_used(vq, ((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 - 1);
        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 (vhost_put_used_idx(vq)) {
                vq_err(vq, "Failed to increment used idx");
                return -EFAULT;
        }
        if (unlikely(vq->log_used)) {
                /* Make sure used idx is seen before log. */
                smp_wmb();
                /* Log used index update. */
                log_used(vq, offsetof(struct vring_used, idx),
                         sizeof vq->used->idx);
                if (vq->log_ctx)
                        eventfd_signal(vq->log_ctx, 1);
        }
        return r;
}
EXPORT_SYMBOL_GPL(vhost_add_used_n);

static bool vhost_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
        __u16 old, new;
        __virtio16 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(vq, VIRTIO_F_NOTIFY_ON_EMPTY) &&
            unlikely(vq->avail_idx == vq->last_avail_idx))
                return true;

        if (!vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX)) {
                __virtio16 flags;
                if (vhost_get_avail_flags(vq, &flags)) {
                        vq_err(vq, "Failed to get flags");
                        return true;
                }
                return !(flags & cpu_to_vhost16(vq, 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 (vhost_get_used_event(vq, &event)) {
                vq_err(vq, "Failed to get used event idx");
                return true;
        }
        return vring_need_event(vhost16_to_cpu(vq, 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.ctx && vhost_notify(dev, vq))
                eventfd_signal(vq->call_ctx.ctx, 1);
}
EXPORT_SYMBOL_GPL(vhost_signal);

/* 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);
}
EXPORT_SYMBOL_GPL(vhost_add_used_and_signal);

/* 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);
}
EXPORT_SYMBOL_GPL(vhost_add_used_and_signal_n);

/* return true if we're sure that avaiable ring is empty */
bool vhost_vq_avail_empty(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
        __virtio16 avail_idx;
        int r;

        if (vq->avail_idx != vq->last_avail_idx)
                return false;

        r = vhost_get_avail_idx(vq, &avail_idx);
        if (unlikely(r))
                return false;
        vq->avail_idx = vhost16_to_cpu(vq, avail_idx);

        return vq->avail_idx == vq->last_avail_idx;
}
EXPORT_SYMBOL_GPL(vhost_vq_avail_empty);

/* OK, now we need to know about added descriptors. */
bool vhost_enable_notify(struct vhost_dev *dev, struct vhost_virtqueue *vq)
{
        __virtio16 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(vq, 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 = vhost_get_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 vhost16_to_cpu(vq, avail_idx) != vq->avail_idx;
}
EXPORT_SYMBOL_GPL(vhost_enable_notify);

/* 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(vq, VIRTIO_RING_F_EVENT_IDX)) {
                r = vhost_update_used_flags(vq);
                if (r)
                        vq_err(vq, "Failed to disable notification at %p: %d\n",
                               &vq->used->flags, r);
        }
}
EXPORT_SYMBOL_GPL(vhost_disable_notify);

/* Create a new message. */
struct vhost_msg_node *vhost_new_msg(struct vhost_virtqueue *vq, int type)
{
        struct vhost_msg_node *node = kmalloc(sizeof *node, GFP_KERNEL);
        if (!node)
                return NULL;

        /* Make sure all padding within the structure is initialized. */
        memset(&node->msg, 0, sizeof node->msg);
        node->vq = vq;
        node->msg.type = type;
        return node;
}
EXPORT_SYMBOL_GPL(vhost_new_msg);

void vhost_enqueue_msg(struct vhost_dev *dev, struct list_head *head,
                       struct vhost_msg_node *node)
{
        spin_lock(&dev->iotlb_lock);
        list_add_tail(&node->node, head);
        spin_unlock(&dev->iotlb_lock);

        wake_up_interruptible_poll(&dev->wait, EPOLLIN | EPOLLRDNORM);
}
EXPORT_SYMBOL_GPL(vhost_enqueue_msg);

struct vhost_msg_node *vhost_dequeue_msg(struct vhost_dev *dev,
                                         struct list_head *head)
{
        struct vhost_msg_node *node = NULL;

        spin_lock(&dev->iotlb_lock);
        if (!list_empty(head)) {
                node = list_first_entry(head, struct vhost_msg_node,
                                        node);
                list_del(&node->node);
        }
        spin_unlock(&dev->iotlb_lock);

        return node;
}
EXPORT_SYMBOL_GPL(vhost_dequeue_msg);

void vhost_set_backend_features(struct vhost_dev *dev, u64 features)
{
        struct vhost_virtqueue *vq;
        int i;

        mutex_lock(&dev->mutex);
        for (i = 0; i < dev->nvqs; ++i) {
                vq = dev->vqs[i];
                mutex_lock(&vq->mutex);
                vq->acked_backend_features = features;
                mutex_unlock(&vq->mutex);
        }
        mutex_unlock(&dev->mutex);
}
EXPORT_SYMBOL_GPL(vhost_set_backend_features);

static int __init vhost_init(void)
{
        return 0;
}

static void __exit vhost_exit(void)
{
}

module_init(vhost_init);
module_exit(vhost_exit);

MODULE_VERSION("0.0.1");
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Michael S. Tsirkin");
MODULE_DESCRIPTION("Host kernel accelerator for virtio");