Initial import

1 files changed, 1583 insertions, 0 deletions

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
new file mode 100644
index 000000000..2ee28266f
--- /dev/null
+++ b/drivers/vhost/vhost.c
@@ -0,0 +1,1583 @@
+/* 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
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.
+ *
+ * Generic code for virtio server in host kernel.
+ */
+
+#include <linux/eventfd.h>
+#include <linux/vhost.h>
+#include <linux/uio.h>
+#include <linux/mm.h>
+#include <linux/mmu_context.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/kthread.h>
+#include <linux/cgroup.h>
+#include <linux/module.h>
+
+#include "vhost.h"
+
+enum {
+	VHOST_MEMORY_MAX_NREGIONS = 64,
+	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])
+
+static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
+			    poll_table *pt)
+{
+	struct vhost_poll *poll;
+
+	poll = container_of(pt, struct vhost_poll, table);
+	poll->wqh = wqh;
+	add_wait_queue(wqh, &poll->wait);
+}
+
+static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
+			     void *key)
+{
+	struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait);
+
+	if (!((unsigned long)key & poll->mask))
+		return 0;
+
+	vhost_poll_queue(poll);
+	return 0;
+}
+
+void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
+{
+	INIT_LIST_HEAD(&work->node);
+	work->fn = fn;
+	init_waitqueue_head(&work->done);
+	work->flushing = 0;
+	work->queue_seq = work->done_seq = 0;
+}
+EXPORT_SYMBOL_GPL(vhost_work_init);
+
+/* Init poll structure */
+void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
+		     unsigned long mask, struct vhost_dev *dev)
+{
+	init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
+	init_poll_funcptr(&poll->table, vhost_poll_func);
+	poll->mask = mask;
+	poll->dev = dev;
+	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)
+{
+	unsigned long mask;
+	int ret = 0;
+
+	if (poll->wqh)
+		return 0;
+
+	mask = file->f_op->poll(file, &poll->table);
+	if (mask)
+		vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
+	if (mask & POLLERR) {
+		if (poll->wqh)
+			remove_wait_queue(poll->wqh, &poll->wait);
+		ret = -EINVAL;
+	}
+
+	return ret;
+}
+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 bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,
+				unsigned seq)
+{
+	int left;
+
+	spin_lock_irq(&dev->work_lock);
+	left = seq - work->done_seq;
+	spin_unlock_irq(&dev->work_lock);
+	return left <= 0;
+}
+
+void vhost_work_flush(struct vhost_dev *dev, struct vhost_work *work)
+{
+	unsigned seq;
+	int flushing;
+
+	spin_lock_irq(&dev->work_lock);
+	seq = work->queue_seq;
+	work->flushing++;
+	spin_unlock_irq(&dev->work_lock);
+	wait_event(work->done, vhost_work_seq_done(dev, work, seq));
+	spin_lock_irq(&dev->work_lock);
+	flushing = --work->flushing;
+	spin_unlock_irq(&dev->work_lock);
+	BUG_ON(flushing < 0);
+}
+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)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&dev->work_lock, flags);
+	if (list_empty(&work->node)) {
+		list_add_tail(&work->node, &dev->work_list);
+		work->queue_seq++;
+		spin_unlock_irqrestore(&dev->work_lock, flags);
+		wake_up_process(dev->worker);
+	} else {
+		spin_unlock_irqrestore(&dev->work_lock, flags);
+	}
+}
+EXPORT_SYMBOL_GPL(vhost_work_queue);
+
+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_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->log_base = NULL;
+	vq->error_ctx = NULL;
+	vq->error = NULL;
+	vq->kick = NULL;
+	vq->call_ctx = NULL;
+	vq->call = NULL;
+	vq->log_ctx = NULL;
+	vq->memory = NULL;
+}
+
+static int vhost_worker(void *data)
+{
+	struct vhost_dev *dev = data;
+	struct vhost_work *work = NULL;
+	unsigned uninitialized_var(seq);
+	mm_segment_t oldfs = get_fs();
+
+	set_fs(USER_DS);
+	use_mm(dev->mm);
+
+	for (;;) {
+		/* mb paired w/ kthread_stop */
+		set_current_state(TASK_INTERRUPTIBLE);
+
+		spin_lock_irq(&dev->work_lock);
+		if (work) {
+			work->done_seq = seq;
+			if (work->flushing)
+				wake_up_all(&work->done);
+		}
+
+		if (kthread_should_stop()) {
+			spin_unlock_irq(&dev->work_lock);
+			__set_current_state(TASK_RUNNING);
+			break;
+		}
+		if (!list_empty(&dev->work_list)) {
+			work = list_first_entry(&dev->work_list,
+						struct vhost_work, node);
+			list_del_init(&work->node);
+			seq = work->queue_seq;
+		} else
+			work = NULL;
+		spin_unlock_irq(&dev->work_lock);
+
+		if (work) {
+			__set_current_state(TASK_RUNNING);
+			work->fn(work);
+			if (need_resched())
+				schedule();
+		} else
+			schedule();
+
+	}
+	unuse_mm(dev->mm);
+	set_fs(oldfs);
+	return 0;
+}
+
+static void vhost_vq_free_iovecs(struct vhost_virtqueue *vq)
+{
+	kfree(vq->indirect);
+	vq->indirect = NULL;
+	kfree(vq->log);
+	vq->log = NULL;
+	kfree(vq->heads);
+	vq->heads = NULL;
+}
+
+/* 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(sizeof *vq->indirect * UIO_MAXIOV,
+				       GFP_KERNEL);
+		vq->log = kmalloc(sizeof *vq->log * UIO_MAXIOV, GFP_KERNEL);
+		vq->heads = kmalloc(sizeof *vq->heads * UIO_MAXIOV, 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]);
+}
+
+void vhost_dev_init(struct vhost_dev *dev,
+		    struct vhost_virtqueue **vqs, int nvqs)
+{
+	struct vhost_virtqueue *vq;
+	int i;
+
+	dev->vqs = vqs;
+	dev->nvqs = nvqs;
+	mutex_init(&dev->mutex);
+	dev->log_ctx = NULL;
+	dev->log_file = NULL;
+	dev->memory = NULL;
+	dev->mm = NULL;
+	spin_lock_init(&dev->work_lock);
+	INIT_LIST_HEAD(&dev->work_list);
+	dev->worker = NULL;
+
+	for (i = 0; i < dev->nvqs; ++i) {
+		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,
+					POLLIN, 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);
+
+/* 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;
+	}
+
+	/* No owner, become one */
+	dev->mm = get_task_mm(current);
+	worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
+	if (IS_ERR(worker)) {
+		err = PTR_ERR(worker);
+		goto err_worker;
+	}
+
+	dev->worker = worker;
+	wake_up_process(worker);	/* avoid contributing to loadavg */
+
+	err = vhost_attach_cgroups(dev);
+	if (err)
+		goto err_cgroup;
+
+	err = vhost_dev_alloc_iovecs(dev);
+	if (err)
+		goto err_cgroup;
+
+	return 0;
+err_cgroup:
+	kthread_stop(worker);
+	dev->worker = NULL;
+err_worker:
+	if (dev->mm)
+		mmput(dev->mm);
+	dev->mm = NULL;
+err_mm:
+	return err;
+}
+EXPORT_SYMBOL_GPL(vhost_dev_set_owner);
+
+struct vhost_memory *vhost_dev_reset_owner_prepare(void)
+{
+	return kmalloc(offsetof(struct vhost_memory, regions), GFP_KERNEL);
+}
+EXPORT_SYMBOL_GPL(vhost_dev_reset_owner_prepare);
+
+/* Caller should have device mutex */
+void vhost_dev_reset_owner(struct vhost_dev *dev, struct vhost_memory *memory)
+{
+	int i;
+
+	vhost_dev_cleanup(dev, true);
+
+	/* Restore memory to default empty mapping. */
+	memory->nregions = 0;
+	dev->memory = memory;
+	/* 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]->memory = memory;
+}
+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);
+
+/* Caller should have device mutex if and only if locked is set */
+void vhost_dev_cleanup(struct vhost_dev *dev, bool locked)
+{
+	int i;
+
+	for (i = 0; i < dev->nvqs; ++i) {
+		if (dev->vqs[i]->error_ctx)
+			eventfd_ctx_put(dev->vqs[i]->error_ctx);
+		if (dev->vqs[i]->error)
+			fput(dev->vqs[i]->error);
+		if (dev->vqs[i]->kick)
+			fput(dev->vqs[i]->kick);
+		if (dev->vqs[i]->call_ctx)
+			eventfd_ctx_put(dev->vqs[i]->call_ctx);
+		if (dev->vqs[i]->call)
+			fput(dev->vqs[i]->call);
+		vhost_vq_reset(dev, dev->vqs[i]);
+	}
+	vhost_dev_free_iovecs(dev);
+	if (dev->log_ctx)
+		eventfd_ctx_put(dev->log_ctx);
+	dev->log_ctx = NULL;
+	if (dev->log_file)
+		fput(dev->log_file);
+	dev->log_file = NULL;
+	/* No one will access memory at this point */
+	kfree(dev->memory);
+	dev->memory = NULL;
+	WARN_ON(!list_empty(&dev->work_list));
+	if (dev->worker) {
+		kthread_stop(dev->worker);
+		dev->worker = NULL;
+	}
+	if (dev->mm)
+		mmput(dev->mm);
+	dev->mm = NULL;
+}
+EXPORT_SYMBOL_GPL(vhost_dev_cleanup);
+
+static int log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
+{
+	u64 a = addr / VHOST_PAGE_SIZE / 8;
+
+	/* Make sure 64 bit math will not overflow. */
+	if (a > ULONG_MAX - (unsigned long)log_base ||
+	    a + (unsigned long)log_base > ULONG_MAX)
+		return 0;
+
+	return access_ok(VERIFY_WRITE, log_base + a,
+			 (sz + VHOST_PAGE_SIZE * 8 - 1) / VHOST_PAGE_SIZE / 8);
+}
+
+/* Caller should have vq mutex and device mutex. */
+static int vq_memory_access_ok(void __user *log_base, struct vhost_memory *mem,
+			       int log_all)
+{
+	int i;
+
+	if (!mem)
+		return 0;
+
+	for (i = 0; i < mem->nregions; ++i) {
+		struct vhost_memory_region *m = mem->regions + i;
+		unsigned long a = m->userspace_addr;
+		if (m->memory_size > ULONG_MAX)
+			return 0;
+		else if (!access_ok(VERIFY_WRITE, (void __user *)a,
+				    m->memory_size))
+			return 0;
+		else if (log_all && !log_access_ok(log_base,
+						   m->guest_phys_addr,
+						   m->memory_size))
+			return 0;
+	}
+	return 1;
+}
+
+/* Can we switch to this memory table? */
+/* Caller should have device mutex but not vq mutex */
+static int memory_access_ok(struct vhost_dev *d, struct vhost_memory *mem,
+			    int log_all)
+{
+	int i;
+
+	for (i = 0; i < d->nvqs; ++i) {
+		int ok;
+		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, mem, log);
+		else
+			ok = 1;
+		mutex_unlock(&d->vqs[i]->mutex);
+		if (!ok)
+			return 0;
+	}
+	return 1;
+}
+
+static int vq_access_ok(struct vhost_virtqueue *vq, unsigned int num,
+			struct vring_desc __user *desc,
+			struct vring_avail __user *avail,
+			struct vring_used __user *used)
+{
+	size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
+	return access_ok(VERIFY_READ, desc, num * sizeof *desc) &&
+	       access_ok(VERIFY_READ, avail,
+			 sizeof *avail + num * sizeof *avail->ring + s) &&
+	       access_ok(VERIFY_WRITE, used,
+			sizeof *used + num * sizeof *used->ring + s);
+}
+
+/* Can we log writes? */
+/* Caller should have device mutex but not vq mutex */
+int vhost_log_access_ok(struct vhost_dev *dev)
+{
+	return memory_access_ok(dev, dev->memory, 1);
+}
+EXPORT_SYMBOL_GPL(vhost_log_access_ok);
+
+/* Verify access for write logging. */
+/* Caller should have vq mutex and device mutex */
+static int vq_log_access_ok(struct vhost_virtqueue *vq,
+			    void __user *log_base)
+{
+	size_t s = vhost_has_feature(vq, VIRTIO_RING_F_EVENT_IDX) ? 2 : 0;
+
+	return vq_memory_access_ok(log_base, vq->memory,
+				   vhost_has_feature(vq, VHOST_F_LOG_ALL)) &&
+		(!vq->log_used || log_access_ok(log_base, vq->log_addr,
+					sizeof *vq->used +
+					vq->num * sizeof *vq->used->ring + s));
+}
+
+/* Can we start vq? */
+/* Caller should have vq mutex and device mutex */
+int vhost_vq_access_ok(struct vhost_virtqueue *vq)
+{
+	return vq_access_ok(vq, vq->num, vq->desc, vq->avail, vq->used) &&
+		vq_log_access_ok(vq, vq->log_base);
+}
+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, *oldmem;
+	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 > VHOST_MEMORY_MAX_NREGIONS)
+		return -E2BIG;
+	newmem = kmalloc(size + mem.nregions * sizeof *m->regions, GFP_KERNEL);
+	if (!newmem)
+		return -ENOMEM;
+
+	memcpy(newmem, &mem, size);
+	if (copy_from_user(newmem->regions, m->regions,
+			   mem.nregions * sizeof *m->regions)) {
+		kfree(newmem);
+		return -EFAULT;
+	}
+
+	if (!memory_access_ok(d, newmem, 0)) {
+		kfree(newmem);
+		return -EFAULT;
+	}
+	oldmem = d->memory;
+	d->memory = newmem;
+
+	/* 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]->memory = newmem;
+		mutex_unlock(&d->vqs[i]->mutex);
+	}
+	kfree(oldmem);
+	return 0;
+}
+
+long vhost_vring_ioctl(struct vhost_dev *d, int ioctl, void __user *argp)
+{
+	struct file *eventfp, *filep = NULL;
+	bool pollstart = false, pollstop = false;
+	struct eventfd_ctx *ctx = NULL;
+	u32 __user *idxp = argp;
+	struct vhost_virtqueue *vq;
+	struct vhost_vring_state s;
+	struct vhost_vring_file f;
+	struct vhost_vring_addr a;
+	u32 idx;
+	long r;
+
+	r = get_user(idx, idxp);
+	if (r < 0)
+		return r;
+	if (idx >= d->nvqs)
+		return -ENOBUFS;
+
+	vq = d->vqs[idx];
+
+	mutex_lock(&vq->mutex);
+
+	switch (ioctl) {
+	case VHOST_SET_VRING_NUM:
+		/* Resizing ring with an active backend?
+		 * You don't want to do that. */
+		if (vq->private_data) {
+			r = -EBUSY;
+			break;
+		}
+		if (copy_from_user(&s, argp, sizeof s)) {
+			r = -EFAULT;
+			break;
+		}
+		if (!s.num || s.num > 0xffff || (s.num & (s.num - 1))) {
+			r = -EINVAL;
+			break;
+		}
+		vq->num = s.num;
+		break;
+	case VHOST_SET_VRING_BASE:
+		/* Moving base with an active backend?
+		 * You don't want to do that. */
+		if (vq->private_data) {
+			r = -EBUSY;
+			break;
+		}
+		if (copy_from_user(&s, argp, sizeof s)) {
+			r = -EFAULT;
+			break;
+		}
+		if (s.num > 0xffff) {
+			r = -EINVAL;
+			break;
+		}
+		vq->last_avail_idx = s.num;
+		/* Forget the cached index value. */
+		vq->avail_idx = vq->last_avail_idx;
+		break;
+	case VHOST_GET_VRING_BASE:
+		s.index = idx;
+		s.num = vq->last_avail_idx;
+		if (copy_to_user(argp, &s, sizeof s))
+			r = -EFAULT;
+		break;
+	case VHOST_SET_VRING_ADDR:
+		if (copy_from_user(&a, argp, sizeof a)) {
+			r = -EFAULT;
+			break;
+		}
+		if (a.flags & ~(0x1 << VHOST_VRING_F_LOG)) {
+			r = -EOPNOTSUPP;
+			break;
+		}
+		/* For 32bit, verify that the top 32bits of the user
+		   data are set to zero. */
+		if ((u64)(unsigned long)a.desc_user_addr != a.desc_user_addr ||
+		    (u64)(unsigned long)a.used_user_addr != a.used_user_addr ||
+		    (u64)(unsigned long)a.avail_user_addr != a.avail_user_addr) {
+			r = -EFAULT;
+			break;
+		}
+
+		/* 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 & (sizeof(u64) - 1))) {
+			r = -EINVAL;
+			break;
+		}
+
+		/* We only verify access here if backend is configured.
+		 * If it is not, we don't as size might not have been setup.
+		 * We will verify when backend is configured. */
+		if (vq->private_data) {
+			if (!vq_access_ok(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)) {
+				r = -EINVAL;
+				break;
+			}
+
+			/* Also validate log access for used ring if enabled. */
+			if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
+			    !log_access_ok(vq->log_base, a.log_guest_addr,
+					   sizeof *vq->used +
+					   vq->num * sizeof *vq->used->ring)) {
+				r = -EINVAL;
+				break;
+			}
+		}
+
+		vq->log_used = !!(a.flags & (0x1 << VHOST_VRING_F_LOG));
+		vq->desc = (void __user *)(unsigned long)a.desc_user_addr;
+		vq->avail = (void __user *)(unsigned long)a.avail_user_addr;
+		vq->log_addr = a.log_guest_addr;
+		vq->used = (void __user *)(unsigned long)a.used_user_addr;
+		break;
+	case VHOST_SET_VRING_KICK:
+		if (copy_from_user(&f, argp, sizeof f)) {
+			r = -EFAULT;
+			break;
+		}
+		eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
+		if (IS_ERR(eventfp)) {
+			r = PTR_ERR(eventfp);
+			break;
+		}
+		if (eventfp != vq->kick) {
+			pollstop = (filep = vq->kick) != NULL;
+			pollstart = (vq->kick = eventfp) != NULL;
+		} else
+			filep = eventfp;
+		break;
+	case VHOST_SET_VRING_CALL:
+		if (copy_from_user(&f, argp, sizeof f)) {
+			r = -EFAULT;
+			break;
+		}
+		eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
+		if (IS_ERR(eventfp)) {
+			r = PTR_ERR(eventfp);
+			break;
+		}
+		if (eventfp != vq->call) {
+			filep = vq->call;
+			ctx = vq->call_ctx;
+			vq->call = eventfp;
+			vq->call_ctx = eventfp ?
+				eventfd_ctx_fileget(eventfp) : NULL;
+		} else
+			filep = eventfp;
+		break;
+	case VHOST_SET_VRING_ERR:
+		if (copy_from_user(&f, argp, sizeof f)) {
+			r = -EFAULT;
+			break;
+		}
+		eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
+		if (IS_ERR(eventfp)) {
+			r = PTR_ERR(eventfp);
+			break;
+		}
+		if (eventfp != vq->error) {
+			filep = vq->error;
+			vq->error = eventfp;
+			ctx = vq->error_ctx;
+			vq->error_ctx = eventfp ?
+				eventfd_ctx_fileget(eventfp) : NULL;
+		} else
+			filep = eventfp;
+		break;
+	default:
+		r = -ENOIOCTLCMD;
+	}
+
+	if (pollstop && vq->handle_kick)
+		vhost_poll_stop(&vq->poll);
+
+	if (ctx)
+		eventfd_ctx_put(ctx);
+	if (filep)
+		fput(filep);
+
+	if (pollstart && vq->handle_kick)
+		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);
+
+/* Caller must have device mutex */
+long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
+{
+	struct file *eventfp, *filep = NULL;
+	struct eventfd_ctx *ctx = NULL;
+	u64 p;
+	long r;
+	int i, fd;
+
+	/* If you are not the owner, you can become one */
+	if (ioctl == VHOST_SET_OWNER) {
+		r = vhost_dev_set_owner(d);
+		goto done;
+	}
+
+	/* You must be the owner to do anything else */
+	r = vhost_dev_check_owner(d);
+	if (r)
+		goto done;
+
+	switch (ioctl) {
+	case VHOST_SET_MEM_TABLE:
+		r = vhost_set_memory(d, argp);
+		break;
+	case VHOST_SET_LOG_BASE:
+		if (copy_from_user(&p, argp, sizeof p)) {
+			r = -EFAULT;
+			break;
+		}
+		if ((u64)(unsigned long)p != p) {
+			r = -EFAULT;
+			break;
+		}
+		for (i = 0; i < d->nvqs; ++i) {
+			struct vhost_virtqueue *vq;
+			void __user *base = (void __user *)(unsigned long)p;
+			vq = d->vqs[i];
+			mutex_lock(&vq->mutex);
+			/* If ring is inactive, will check when it's enabled. */
+			if (vq->private_data && !vq_log_access_ok(vq, base))
+				r = -EFAULT;
+			else
+				vq->log_base = base;
+			mutex_unlock(&vq->mutex);
+		}
+		break;
+	case VHOST_SET_LOG_FD:
+		r = get_user(fd, (int __user *)argp);
+		if (r < 0)
+			break;
+		eventfp = fd == -1 ? NULL : eventfd_fget(fd);
+		if (IS_ERR(eventfp)) {
+			r = PTR_ERR(eventfp);
+			break;
+		}
+		if (eventfp != d->log_file) {
+			filep = d->log_file;
+			ctx = d->log_ctx;
+			d->log_ctx = eventfp ?
+				eventfd_ctx_fileget(eventfp) : NULL;
+		} else
+			filep = eventfp;
+		for (i = 0; i < d->nvqs; ++i) {
+			mutex_lock(&d->vqs[i]->mutex);
+			d->vqs[i]->log_ctx = d->log_ctx;
+			mutex_unlock(&d->vqs[i]->mutex);
+		}
+		if (ctx)
+			eventfd_ctx_put(ctx);
+		if (filep)
+			fput(filep);
+		break;
+	default:
+		r = -ENOIOCTLCMD;
+		break;
+	}
+done:
+	return r;
+}
+EXPORT_SYMBOL_GPL(vhost_dev_ioctl);
+
+static const struct vhost_memory_region *find_region(struct vhost_memory *mem,
+						     __u64 addr, __u32 len)
+{
+	struct vhost_memory_region *reg;
+	int i;
+
+	/* linear search is not brilliant, but we really have on the order of 6
+	 * regions in practice */
+	for (i = 0; i < mem->nregions; ++i) {
+		reg = mem->regions + i;
+		if (reg->guest_phys_addr <= addr &&
+		    reg->guest_phys_addr + reg->memory_size - 1 >= addr)
+			return reg;
+	}
+	return NULL;
+}
+
+/* TODO: This is really inefficient.  We need something like get_user()
+ * (instruction directly accesses the data, with an exception table entry
+ * returning -EFAULT). See Documentation/x86/exception-tables.txt.
+ */
+static int set_bit_to_user(int nr, void __user *addr)
+{
+	unsigned long log = (unsigned long)addr;
+	struct page *page;
+	void *base;
+	int bit = nr + (log % PAGE_SIZE) * 8;
+	int r;
+
+	r = get_user_pages_fast(log, 1, 1, &page);
+	if (r < 0)
+		return r;
+	BUG_ON(r != 1);
+	base = kmap_atomic(page);
+	set_bit(bit, base);
+	kunmap_atomic(base);
+	set_page_dirty_lock(page);
+	put_page(page);
+	return 0;
+}
+
+static int log_write(void __user *log_base,
+		     u64 write_address, u64 write_length)
+{
+	u64 write_page = write_address / VHOST_PAGE_SIZE;
+	int r;
+
+	if (!write_length)
+		return 0;
+	write_length += write_address % VHOST_PAGE_SIZE;
+	for (;;) {
+		u64 base = (u64)(unsigned long)log_base;
+		u64 log = base + write_page / 8;
+		int bit = write_page % 8;
+		if ((u64)(unsigned long)log != log)
+			return -EFAULT;
+		r = set_bit_to_user(bit, (void __user *)(unsigned long)log);
+		if (r < 0)
+			return r;
+		if (write_length <= VHOST_PAGE_SIZE)
+			break;
+		write_length -= VHOST_PAGE_SIZE;
+		write_page += 1;
+	}
+	return r;
+}
+
+int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
+		    unsigned int log_num, u64 len)
+{
+	int i, r;
+
+	/* Make sure data written is seen before log. */
+	smp_wmb();
+	for (i = 0; i < log_num; ++i) {
+		u64 l = min(log[i].len, len);
+		r = log_write(vq->log_base, log[i].addr, l);
+		if (r < 0)
+			return r;
+		len -= l;
+		if (!len) {
+			if (vq->log_ctx)
+				eventfd_signal(vq->log_ctx, 1);
+			return 0;
+		}
+	}
+	/* Length written exceeds what we have stored. This is a bug. */
+	BUG();
+	return 0;
+}
+EXPORT_SYMBOL_GPL(vhost_log_write);
+
+static int vhost_update_used_flags(struct vhost_virtqueue *vq)
+{
+	void __user *used;
+	if (__put_user(cpu_to_vhost16(vq, vq->used_flags), &vq->used->flags) < 0)
+		return -EFAULT;
+	if (unlikely(vq->log_used)) {
+		/* Make sure the flag is seen before log. */
+		smp_wmb();
+		/* Log used flag write. */
+		used = &vq->used->flags;
+		log_write(vq->log_base, vq->log_addr +
+			  (used - (void __user *)vq->used),
+			  sizeof vq->used->flags);
+		if (vq->log_ctx)
+			eventfd_signal(vq->log_ctx, 1);
+	}
+	return 0;
+}
+
+static int vhost_update_avail_event(struct vhost_virtqueue *vq, u16 avail_event)
+{
+	if (__put_user(cpu_to_vhost16(vq, vq->avail_idx), vhost_avail_event(vq)))
+		return -EFAULT;
+	if (unlikely(vq->log_used)) {
+		void __user *used;
+		/* Make sure the event is seen before log. */
+		smp_wmb();
+		/* Log avail event write */
+		used = vhost_avail_event(vq);
+		log_write(vq->log_base, vq->log_addr +
+			  (used - (void __user *)vq->used),
+			  sizeof *vhost_avail_event(vq));
+		if (vq->log_ctx)
+			eventfd_signal(vq->log_ctx, 1);
+	}
+	return 0;
+}
+
+int vhost_init_used(struct vhost_virtqueue *vq)
+{
+	__virtio16 last_used_idx;
+	int r;
+	if (!vq->private_data)
+		return 0;
+
+	r = vhost_update_used_flags(vq);
+	if (r)
+		return r;
+	vq->signalled_used_valid = false;
+	if (!access_ok(VERIFY_READ, &vq->used->idx, sizeof vq->used->idx))
+		return -EFAULT;
+	r = __get_user(last_used_idx, &vq->used->idx);
+	if (r)
+		return r;
+	vq->last_used_idx = vhost16_to_cpu(vq, last_used_idx);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(vhost_init_used);
+
+static int translate_desc(struct vhost_virtqueue *vq, u64 addr, u32 len,
+			  struct iovec iov[], int iov_size)
+{
+	const struct vhost_memory_region *reg;
+	struct vhost_memory *mem;
+	struct iovec *_iov;
+	u64 s = 0;
+	int ret = 0;
+
+	mem = vq->memory;
+	while ((u64)len > s) {
+		u64 size;
+		if (unlikely(ret >= iov_size)) {
+			ret = -ENOBUFS;
+			break;
+		}
+		reg = find_region(mem, addr, len);
+		if (unlikely(!reg)) {
+			ret = -EFAULT;
+			break;
+		}
+		_iov = iov + ret;
+		size = reg->memory_size - addr + reg->guest_phys_addr;
+		_iov->iov_len = min((u64)len - s, size);
+		_iov->iov_base = (void __user *)(unsigned long)
+			(reg->userspace_addr + addr - reg->guest_phys_addr);
+		s += size;
+		addr += size;
+		++ret;
+	}
+
+	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, desc->next);
+	/* Make sure compiler knows to grab that: we don't want it changing! */
+	/* We will use the result as an index in an array, so most
+	 * architectures only need a compiler barrier here. */
+	read_barrier_depends();
+
+	return next;
+}
+
+static int get_indirect(struct vhost_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;
+
+	/* 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);
+	if (unlikely(ret < 0)) {
+		vq_err(vq, "Translation failure %d in indirect.\n", ret);
+		return ret;
+	}
+	iov_iter_init(&from, READ, vq->indirect, ret, len);
+
+	/* We will use the result as an address to read from, so most
+	 * architectures only need a compiler barrier here. */
+	read_barrier_depends();
+
+	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(&desc, sizeof(desc), &from) !=
+			     sizeof(desc))) {
+			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;
+		}
+
+		ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
+				     vhost32_to_cpu(vq, desc.len), iov + iov_count,
+				     iov_size - iov_count);
+		if (unlikely(ret < 0)) {
+			vq_err(vq, "Translation failure %d indirect idx %d\n",
+			       ret, i);
+			return ret;
+		}
+		/* If this is an input descriptor, increment that count. */
+		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE)) {
+			*in_num += ret;
+			if (unlikely(log)) {
+				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;
+
+	/* Check it isn't doing very strange things with descriptor numbers. */
+	last_avail_idx = vq->last_avail_idx;
+	if (unlikely(__get_user(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(__get_user(ring_head,
+				&vq->avail->ring[last_avail_idx % vq->num]))) {
+		vq_err(vq, "Failed to read head: idx %d address %p\n",
+		       last_avail_idx,
+		       &vq->avail->ring[last_avail_idx % vq->num]);
+		return -EFAULT;
+	}
+
+	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 = __copy_from_user(&desc, vq->desc + i, sizeof desc);
+		if (unlikely(ret)) {
+			vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
+			       i, vq->desc + i);
+			return -EFAULT;
+		}
+		if (desc.flags & 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)) {
+				vq_err(vq, "Failure detected "
+				       "in indirect descriptor at idx %d\n", i);
+				return ret;
+			}
+			continue;
+		}
+
+		ret = translate_desc(vq, vhost64_to_cpu(vq, desc.addr),
+				     vhost32_to_cpu(vq, desc.len), iov + iov_count,
+				     iov_size - iov_count);
+		if (unlikely(ret < 0)) {
+			vq_err(vq, "Translation failure %d descriptor idx %d\n",
+			       ret, i);
+			return ret;
+		}
+		if (desc.flags & cpu_to_vhost16(vq, VRING_DESC_F_WRITE)) {
+			/* If this is an input descriptor,
+			 * increment that count. */
+			*in_num += ret;
+			if (unlikely(log)) {
+				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)
+{
+	struct vring_used_elem __user *used;
+	u16 old, new;
+	int start;
+
+	start = vq->last_used_idx % vq->num;
+	used = vq->used->ring + start;
+	if (count == 1) {
+		if (__put_user(heads[0].id, &used->id)) {
+			vq_err(vq, "Failed to write used id");
+			return -EFAULT;
+		}
+		if (__put_user(heads[0].len, &used->len)) {
+			vq_err(vq, "Failed to write used len");
+			return -EFAULT;
+		}
+	} else if (__copy_to_user(used, heads, count * sizeof *used)) {
+		vq_err(vq, "Failed to write used");
+		return -EFAULT;
+	}
+	if (unlikely(vq->log_used)) {
+		/* Make sure data is seen before log. */
+		smp_wmb();
+		/* Log used ring entry write. */
+		log_write(vq->log_base,
+			  vq->log_addr +
+			   ((void __user *)used - (void __user *)vq->used),
+			  count * sizeof *used);
+	}
+	old = vq->last_used_idx;
+	new = (vq->last_used_idx += count);
+	/* If the driver never bothers to signal in a very long while,
+	 * used index might wrap around. If that happens, invalidate
+	 * signalled_used index we stored. TODO: make sure driver
+	 * signals at least once in 2^16 and remove this. */
+	if (unlikely((u16)(new - vq->signalled_used) < (u16)(new - old)))
+		vq->signalled_used_valid = false;
+	return 0;
+}
+
+/* After we've used one of their buffers, we tell them about it.  We'll then
+ * want to notify the guest, using eventfd. */
+int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
+		     unsigned count)
+{
+	int start, n, r;
+
+	start = vq->last_used_idx % vq->num;
+	n = vq->num - start;
+	if (n < count) {
+		r = __vhost_add_used_n(vq, heads, n);
+		if (r < 0)
+			return r;
+		heads += n;
+		count -= n;
+	}
+	r = __vhost_add_used_n(vq, heads, count);
+
+	/* Make sure buffer is written before we update index. */
+	smp_wmb();
+	if (__put_user(cpu_to_vhost16(vq, vq->last_used_idx), &vq->used->idx)) {
+		vq_err(vq, "Failed to increment used idx");
+		return -EFAULT;
+	}
+	if (unlikely(vq->log_used)) {
+		/* Log used index update. */
+		log_write(vq->log_base,
+			  vq->log_addr + offsetof(struct vring_used, idx),
+			  sizeof vq->used->idx);
+		if (vq->log_ctx)
+			eventfd_signal(vq->log_ctx, 1);
+	}
+	return r;
+}
+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 (__get_user(flags, &vq->avail->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 (__get_user(event, vhost_used_event(vq))) {
+		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 && vhost_notify(dev, vq))
+		eventfd_signal(vq->call_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);
+
+/* 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 = __get_user(avail_idx, &vq->avail->idx);
+	if (r) {
+		vq_err(vq, "Failed to check avail idx at %p: %d\n",
+		       &vq->avail->idx, r);
+		return false;
+	}
+
+	return 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 enable notification at %p: %d\n",
+			       &vq->used->flags, r);
+	}
+}
+EXPORT_SYMBOL_GPL(vhost_disable_notify);
+
+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");