Adding upstream version 6.6.15.upstream/6.6.15

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 2937 insertions, 0 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
new file mode 100644
index 0000000000..e0c181ad17
--- /dev/null
+++ b/drivers/vhost/vhost.c
@@ -0,0 +1,2937 @@
+// 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/module.h>
+#include <linux/sort.h>
+#include <linux/sched/mm.h>
+#include <linux/sched/signal.h>
+#include <linux/sched/vhost_task.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,
+		     struct vhost_virtqueue *vq)
+{
+	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;
+	poll->vq = vq;
+
+	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);
+
+static void vhost_worker_queue(struct vhost_worker *worker,
+			       struct vhost_work *work)
+{
+	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, &worker->work_list);
+		vhost_task_wake(worker->vtsk);
+	}
+}
+
+bool vhost_vq_work_queue(struct vhost_virtqueue *vq, struct vhost_work *work)
+{
+	struct vhost_worker *worker;
+	bool queued = false;
+
+	rcu_read_lock();
+	worker = rcu_dereference(vq->worker);
+	if (worker) {
+		queued = true;
+		vhost_worker_queue(worker, work);
+	}
+	rcu_read_unlock();
+
+	return queued;
+}
+EXPORT_SYMBOL_GPL(vhost_vq_work_queue);
+
+void vhost_vq_flush(struct vhost_virtqueue *vq)
+{
+	struct vhost_flush_struct flush;
+
+	init_completion(&flush.wait_event);
+	vhost_work_init(&flush.work, vhost_flush_work);
+
+	if (vhost_vq_work_queue(vq, &flush.work))
+		wait_for_completion(&flush.wait_event);
+}
+EXPORT_SYMBOL_GPL(vhost_vq_flush);
+
+/**
+ * vhost_worker_flush - flush a worker
+ * @worker: worker to flush
+ *
+ * This does not use RCU to protect the worker, so the device or worker
+ * mutex must be held.
+ */
+static void vhost_worker_flush(struct vhost_worker *worker)
+{
+	struct vhost_flush_struct flush;
+
+	init_completion(&flush.wait_event);
+	vhost_work_init(&flush.work, vhost_flush_work);
+
+	vhost_worker_queue(worker, &flush.work);
+	wait_for_completion(&flush.wait_event);
+}
+
+void vhost_dev_flush(struct vhost_dev *dev)
+{
+	struct vhost_worker *worker;
+	unsigned long i;
+
+	xa_for_each(&dev->worker_xa, i, worker) {
+		mutex_lock(&worker->mutex);
+		if (!worker->attachment_cnt) {
+			mutex_unlock(&worker->mutex);
+			continue;
+		}
+		vhost_worker_flush(worker);
+		mutex_unlock(&worker->mutex);
+	}
+}
+EXPORT_SYMBOL_GPL(vhost_dev_flush);
+
+/* A lockless hint for busy polling code to exit the loop */
+bool vhost_vq_has_work(struct vhost_virtqueue *vq)
+{
+	struct vhost_worker *worker;
+	bool has_work = false;
+
+	rcu_read_lock();
+	worker = rcu_dereference(vq->worker);
+	if (worker && !llist_empty(&worker->work_list))
+		has_work = true;
+	rcu_read_unlock();
+
+	return has_work;
+}
+EXPORT_SYMBOL_GPL(vhost_vq_has_work);
+
+void vhost_poll_queue(struct vhost_poll *poll)
+{
+	vhost_vq_work_queue(poll->vq, &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;
+	rcu_assign_pointer(vq->worker, NULL);
+	vhost_vring_call_reset(&vq->call_ctx);
+	__vhost_vq_meta_reset(vq);
+}
+
+static bool vhost_worker(void *data)
+{
+	struct vhost_worker *worker = data;
+	struct vhost_work *work, *work_next;
+	struct llist_node *node;
+
+	node = llist_del_all(&worker->work_list);
+	if (node) {
+		__set_current_state(TASK_RUNNING);
+
+		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);
+			kcov_remote_start_common(worker->kcov_handle);
+			work->fn(work);
+			kcov_remote_stop();
+			cond_resched();
+		}
+	}
+
+	return !!node;
+}
+
+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 size_add(struct_size(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 size_add(struct_size(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, u32 asid,
+				       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->iov_limit = iov_limit;
+	dev->weight = weight;
+	dev->byte_weight = byte_weight;
+	dev->use_worker = use_worker;
+	dev->msg_handler = msg_handler;
+	init_waitqueue_head(&dev->wait);
+	INIT_LIST_HEAD(&dev->read_list);
+	INIT_LIST_HEAD(&dev->pending_list);
+	spin_lock_init(&dev->iotlb_lock);
+	xa_init_flags(&dev->worker_xa, XA_FLAGS_ALLOC);
+
+	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, vq);
+	}
+}
+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);
+
+/* 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;
+}
+
+static void vhost_worker_destroy(struct vhost_dev *dev,
+				 struct vhost_worker *worker)
+{
+	if (!worker)
+		return;
+
+	WARN_ON(!llist_empty(&worker->work_list));
+	xa_erase(&dev->worker_xa, worker->id);
+	vhost_task_stop(worker->vtsk);
+	kfree(worker);
+}
+
+static void vhost_workers_free(struct vhost_dev *dev)
+{
+	struct vhost_worker *worker;
+	unsigned long i;
+
+	if (!dev->use_worker)
+		return;
+
+	for (i = 0; i < dev->nvqs; i++)
+		rcu_assign_pointer(dev->vqs[i]->worker, NULL);
+	/*
+	 * Free the default worker we created and cleanup workers userspace
+	 * created but couldn't clean up (it forgot or crashed).
+	 */
+	xa_for_each(&dev->worker_xa, i, worker)
+		vhost_worker_destroy(dev, worker);
+	xa_destroy(&dev->worker_xa);
+}
+
+static struct vhost_worker *vhost_worker_create(struct vhost_dev *dev)
+{
+	struct vhost_worker *worker;
+	struct vhost_task *vtsk;
+	char name[TASK_COMM_LEN];
+	int ret;
+	u32 id;
+
+	worker = kzalloc(sizeof(*worker), GFP_KERNEL_ACCOUNT);
+	if (!worker)
+		return NULL;
+
+	snprintf(name, sizeof(name), "vhost-%d", current->pid);
+
+	vtsk = vhost_task_create(vhost_worker, worker, name);
+	if (!vtsk)
+		goto free_worker;
+
+	mutex_init(&worker->mutex);
+	init_llist_head(&worker->work_list);
+	worker->kcov_handle = kcov_common_handle();
+	worker->vtsk = vtsk;
+
+	vhost_task_start(vtsk);
+
+	ret = xa_alloc(&dev->worker_xa, &id, worker, xa_limit_32b, GFP_KERNEL);
+	if (ret < 0)
+		goto stop_worker;
+	worker->id = id;
+
+	return worker;
+
+stop_worker:
+	vhost_task_stop(vtsk);
+free_worker:
+	kfree(worker);
+	return NULL;
+}
+
+/* Caller must have device mutex */
+static void __vhost_vq_attach_worker(struct vhost_virtqueue *vq,
+				     struct vhost_worker *worker)
+{
+	struct vhost_worker *old_worker;
+
+	old_worker = rcu_dereference_check(vq->worker,
+					   lockdep_is_held(&vq->dev->mutex));
+
+	mutex_lock(&worker->mutex);
+	worker->attachment_cnt++;
+	mutex_unlock(&worker->mutex);
+	rcu_assign_pointer(vq->worker, worker);
+
+	if (!old_worker)
+		return;
+	/*
+	 * Take the worker mutex to make sure we see the work queued from
+	 * device wide flushes which doesn't use RCU for execution.
+	 */
+	mutex_lock(&old_worker->mutex);
+	old_worker->attachment_cnt--;
+	/*
+	 * We don't want to call synchronize_rcu for every vq during setup
+	 * because it will slow down VM startup. If we haven't done
+	 * VHOST_SET_VRING_KICK and not done the driver specific
+	 * SET_ENDPOINT/RUNNUNG then we can skip the sync since there will
+	 * not be any works queued for scsi and net.
+	 */
+	mutex_lock(&vq->mutex);
+	if (!vhost_vq_get_backend(vq) && !vq->kick) {
+		mutex_unlock(&vq->mutex);
+		mutex_unlock(&old_worker->mutex);
+		/*
+		 * vsock can queue anytime after VHOST_VSOCK_SET_GUEST_CID.
+		 * Warn if it adds support for multiple workers but forgets to
+		 * handle the early queueing case.
+		 */
+		WARN_ON(!old_worker->attachment_cnt &&
+			!llist_empty(&old_worker->work_list));
+		return;
+	}
+	mutex_unlock(&vq->mutex);
+
+	/* Make sure new vq queue/flush/poll calls see the new worker */
+	synchronize_rcu();
+	/* Make sure whatever was queued gets run */
+	vhost_worker_flush(old_worker);
+	mutex_unlock(&old_worker->mutex);
+}
+
+ /* Caller must have device mutex */
+static int vhost_vq_attach_worker(struct vhost_virtqueue *vq,
+				  struct vhost_vring_worker *info)
+{
+	unsigned long index = info->worker_id;
+	struct vhost_dev *dev = vq->dev;
+	struct vhost_worker *worker;
+
+	if (!dev->use_worker)
+		return -EINVAL;
+
+	worker = xa_find(&dev->worker_xa, &index, UINT_MAX, XA_PRESENT);
+	if (!worker || worker->id != info->worker_id)
+		return -ENODEV;
+
+	__vhost_vq_attach_worker(vq, worker);
+	return 0;
+}
+
+/* Caller must have device mutex */
+static int vhost_new_worker(struct vhost_dev *dev,
+			    struct vhost_worker_state *info)
+{
+	struct vhost_worker *worker;
+
+	worker = vhost_worker_create(dev);
+	if (!worker)
+		return -ENOMEM;
+
+	info->worker_id = worker->id;
+	return 0;
+}
+
+/* Caller must have device mutex */
+static int vhost_free_worker(struct vhost_dev *dev,
+			     struct vhost_worker_state *info)
+{
+	unsigned long index = info->worker_id;
+	struct vhost_worker *worker;
+
+	worker = xa_find(&dev->worker_xa, &index, UINT_MAX, XA_PRESENT);
+	if (!worker || worker->id != info->worker_id)
+		return -ENODEV;
+
+	mutex_lock(&worker->mutex);
+	if (worker->attachment_cnt) {
+		mutex_unlock(&worker->mutex);
+		return -EBUSY;
+	}
+	mutex_unlock(&worker->mutex);
+
+	vhost_worker_destroy(dev, worker);
+	return 0;
+}
+
+static int vhost_get_vq_from_user(struct vhost_dev *dev, void __user *argp,
+				  struct vhost_virtqueue **vq, u32 *id)
+{
+	u32 __user *idxp = argp;
+	u32 idx;
+	long r;
+
+	r = get_user(idx, idxp);
+	if (r < 0)
+		return r;
+
+	if (idx >= dev->nvqs)
+		return -ENOBUFS;
+
+	idx = array_index_nospec(idx, dev->nvqs);
+
+	*vq = dev->vqs[idx];
+	*id = idx;
+	return 0;
+}
+
+/* Caller must have device mutex */
+long vhost_worker_ioctl(struct vhost_dev *dev, unsigned int ioctl,
+			void __user *argp)
+{
+	struct vhost_vring_worker ring_worker;
+	struct vhost_worker_state state;
+	struct vhost_worker *worker;
+	struct vhost_virtqueue *vq;
+	long ret;
+	u32 idx;
+
+	if (!dev->use_worker)
+		return -EINVAL;
+
+	if (!vhost_dev_has_owner(dev))
+		return -EINVAL;
+
+	ret = vhost_dev_check_owner(dev);
+	if (ret)
+		return ret;
+
+	switch (ioctl) {
+	/* dev worker ioctls */
+	case VHOST_NEW_WORKER:
+		ret = vhost_new_worker(dev, &state);
+		if (!ret && copy_to_user(argp, &state, sizeof(state)))
+			ret = -EFAULT;
+		return ret;
+	case VHOST_FREE_WORKER:
+		if (copy_from_user(&state, argp, sizeof(state)))
+			return -EFAULT;
+		return vhost_free_worker(dev, &state);
+	/* vring worker ioctls */
+	case VHOST_ATTACH_VRING_WORKER:
+	case VHOST_GET_VRING_WORKER:
+		break;
+	default:
+		return -ENOIOCTLCMD;
+	}
+
+	ret = vhost_get_vq_from_user(dev, argp, &vq, &idx);
+	if (ret)
+		return ret;
+
+	switch (ioctl) {
+	case VHOST_ATTACH_VRING_WORKER:
+		if (copy_from_user(&ring_worker, argp, sizeof(ring_worker))) {
+			ret = -EFAULT;
+			break;
+		}
+
+		ret = vhost_vq_attach_worker(vq, &ring_worker);
+		break;
+	case VHOST_GET_VRING_WORKER:
+		worker = rcu_dereference_check(vq->worker,
+					       lockdep_is_held(&dev->mutex));
+		if (!worker) {
+			ret = -EINVAL;
+			break;
+		}
+
+		ring_worker.index = idx;
+		ring_worker.worker_id = worker->id;
+
+		if (copy_to_user(argp, &ring_worker, sizeof(ring_worker)))
+			ret = -EFAULT;
+		break;
+	default:
+		ret = -ENOIOCTLCMD;
+		break;
+	}
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(vhost_worker_ioctl);
+
+/* Caller should have device mutex */
+long vhost_dev_set_owner(struct vhost_dev *dev)
+{
+	struct vhost_worker *worker;
+	int err, i;
+
+	/* Is there an owner already? */
+	if (vhost_dev_has_owner(dev)) {
+		err = -EBUSY;
+		goto err_mm;
+	}
+
+	vhost_attach_mm(dev);
+
+	err = vhost_dev_alloc_iovecs(dev);
+	if (err)
+		goto err_iovecs;
+
+	if (dev->use_worker) {
+		/*
+		 * This should be done last, because vsock can queue work
+		 * before VHOST_SET_OWNER so it simplifies the failure path
+		 * below since we don't have to worry about vsock queueing
+		 * while we free the worker.
+		 */
+		worker = vhost_worker_create(dev);
+		if (!worker) {
+			err = -ENOMEM;
+			goto err_worker;
+		}
+
+		for (i = 0; i < dev->nvqs; i++)
+			__vhost_vq_attach_worker(dev->vqs[i], worker);
+	}
+
+	return 0;
+
+err_worker:
+	vhost_dev_free_iovecs(dev);
+err_iovecs:
+	vhost_detach_mm(dev);
+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_dev_flush(dev);
+}
+EXPORT_SYMBOL_GPL(vhost_dev_stop);
+
+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);
+}
+EXPORT_SYMBOL_GPL(vhost_clear_msg);
+
+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);
+	vhost_workers_free(dev);
+	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);
+}
+
+/* Make sure 64 bit math will not overflow. */
+static bool vhost_overflow(u64 uaddr, u64 size)
+{
+	if (uaddr > ULONG_MAX || size > ULONG_MAX)
+		return true;
+
+	if (!size)
+		return false;
+
+	return uaddr > ULONG_MAX - size + 1;
+}
+
+/* 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, ITER_DEST, 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, ITER_SOURCE, 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, u32 asid,
+				   struct vhost_iotlb_msg *msg)
+{
+	int ret = 0;
+
+	if (asid != 0)
+		return -EINVAL;
+
+	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;
+	u32 asid = 0;
+
+	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:
+		if (vhost_backend_has_feature(dev->vqs[0],
+					      VHOST_BACKEND_F_IOTLB_ASID)) {
+			ret = copy_from_iter(&asid, sizeof(asid), from);
+			if (ret != sizeof(asid)) {
+				ret = -EINVAL;
+				goto done;
+			}
+			offset = 0;
+		} else
+			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 (msg.type == VHOST_IOTLB_UPDATE && msg.size == 0) {
+		ret = -EINVAL;
+		goto done;
+	}
+
+	if (dev->msg_handler)
+		ret = dev->msg_handler(dev, asid, &msg);
+	else
+		ret = vhost_process_iotlb_msg(dev, asid, &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;
+	struct vhost_virtqueue *vq;
+	struct vhost_vring_state s;
+	struct vhost_vring_file f;
+	u32 idx;
+	long r;
+
+	r = vhost_get_vq_from_user(d, argp, &vq, &idx);
+	if (r < 0)
+		return r;
+
+	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 (vhost_has_feature(vq, VIRTIO_F_RING_PACKED)) {
+			vq->last_avail_idx = s.num & 0xffff;
+			vq->last_used_idx = (s.num >> 16) & 0xffff;
+		} else {
+			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;
+		if (vhost_has_feature(vq, VIRTIO_F_RING_PACKED))
+			s.num = (u32)vq->last_avail_idx | ((u32)vq->last_used_idx << 16);
+		else
+			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_dev_flush(vq->poll.dev);
+	return r;
+}
+EXPORT_SYMBOL_GPL(vhost_vring_ioctl);
+
+int vhost_init_device_iotlb(struct vhost_dev *d)
+{
+	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/arch/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)
+{
+	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, last = addr + len - 1;
+	int ret = 0;
+
+	while ((u64)len > s) {
+		u64 size;
+		if (unlikely(ret >= iov_size)) {
+			ret = -ENOBUFS;
+			break;
+		}
+
+		map = vhost_iotlb_itree_first(umem, addr, last);
+		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, ITER_SOURCE, 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);
+		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;
+	}
+	vq->avail_idx = vhost16_to_cpu(vq, avail_idx);
+
+	return vq->avail_idx != vq->last_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)
+{
+	/* Make sure all padding within the structure is initialized. */
+	struct vhost_msg_node *node = kzalloc(sizeof(*node), GFP_KERNEL);
+	if (!node)
+		return NULL;
+
+	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");