drivers/vhost/vhost.c

   1 /* Copyright (C) 2009 Red Hat, Inc.
   2  * Copyright (C) 2006 Rusty Russell IBM Corporation
   3  *
   4  * Author: Michael S. Tsirkin <mst@redhat.com>
   5  *
   6  * Inspiration, some code, and most witty comments come from
   7  * Documentation/lguest/lguest.c, by Rusty Russell
   8  *
   9  * This work is licensed under the terms of the GNU GPL, version 2.
  10  *
  11  * Generic code for virtio server in host kernel.
  12  */
  13
  14 #include <linux/eventfd.h>
  15 #include <linux/vhost.h>
  16 #include <linux/virtio_net.h>
  17 #include <linux/mm.h>
  18 #include <linux/mmu_context.h>
  19 #include <linux/miscdevice.h>
  20 #include <linux/mutex.h>
  21 #include <linux/rcupdate.h>
  22 #include <linux/poll.h>
  23 #include <linux/file.h>
  24 #include <linux/highmem.h>
  25 #include <linux/slab.h>
  26 #include <linux/kthread.h>
  27 #include <linux/cgroup.h>
  28
  29 #include <linux/net.h>
  30 #include <linux/if_packet.h>
  31 #include <linux/if_arp.h>
  32
  33 #include "vhost.h"
  34
  35 enum {
  36         VHOST_MEMORY_MAX_NREGIONS = 64,
  37         VHOST_MEMORY_F_LOG = 0x1,
  38 };
  39
  40 static void vhost_poll_func(struct file *file, wait_queue_head_t *wqh,
  41                             poll_table *pt)
  42 {
  43         struct vhost_poll *poll;
  44         poll = container_of(pt, struct vhost_poll, table);
  45
  46         poll->wqh = wqh;
  47         add_wait_queue(wqh, &poll->wait);
  48 }
  49
  50 static int vhost_poll_wakeup(wait_queue_t *wait, unsigned mode, int sync,
  51                              void *key)
  52 {
  53         struct vhost_poll *poll = container_of(wait, struct vhost_poll, wait);
  54
  55         if (!((unsigned long)key & poll->mask))
  56                 return 0;
  57
  58         vhost_poll_queue(poll);
  59         return 0;
  60 }
  61
  62 static void vhost_work_init(struct vhost_work *work, vhost_work_fn_t fn)
  63 {
  64         INIT_LIST_HEAD(&work->node);
  65         work->fn = fn;
  66         init_waitqueue_head(&work->done);
  67         work->flushing = 0;
  68         work->queue_seq = work->done_seq = 0;
  69 }
  70
  71 /* Init poll structure */
  72 void vhost_poll_init(struct vhost_poll *poll, vhost_work_fn_t fn,
  73                      unsigned long mask, struct vhost_dev *dev)
  74 {
  75         init_waitqueue_func_entry(&poll->wait, vhost_poll_wakeup);
  76         init_poll_funcptr(&poll->table, vhost_poll_func);
  77         poll->mask = mask;
  78         poll->dev = dev;
  79
  80         vhost_work_init(&poll->work, fn);
  81 }
  82
  83 /* Start polling a file. We add ourselves to file's wait queue. The caller must
  84  * keep a reference to a file until after vhost_poll_stop is called. */
  85 void vhost_poll_start(struct vhost_poll *poll, struct file *file)
  86 {
  87         unsigned long mask;
  88         mask = file->f_op->poll(file, &poll->table);
  89         if (mask)
  90                 vhost_poll_wakeup(&poll->wait, 0, 0, (void *)mask);
  91 }
  92
  93 /* Stop polling a file. After this function returns, it becomes safe to drop the
  94  * file reference. You must also flush afterwards. */
  95 void vhost_poll_stop(struct vhost_poll *poll)
  96 {
  97         remove_wait_queue(poll->wqh, &poll->wait);
  98 }
  99
 100 static bool vhost_work_seq_done(struct vhost_dev *dev, struct vhost_work *work,
 101                                 unsigned seq)
 102 {
 103         int left;
 104         spin_lock_irq(&dev->work_lock);
 105         left = seq - work->done_seq;
 106         spin_unlock_irq(&dev->work_lock);
 107         return left <= 0;
 108 }
 109
 110 static void vhost_work_flush(struct vhost_dev *dev, struct vhost_work *work)
 111 {
 112         unsigned seq;
 113         int flushing;
 114
 115         spin_lock_irq(&dev->work_lock);
 116         seq = work->queue_seq;
 117         work->flushing++;
 118         spin_unlock_irq(&dev->work_lock);
 119         wait_event(work->done, vhost_work_seq_done(dev, work, seq));
 120         spin_lock_irq(&dev->work_lock);
 121         flushing = --work->flushing;
 122         spin_unlock_irq(&dev->work_lock);
 123         BUG_ON(flushing < 0);
 124 }
 125
 126 /* Flush any work that has been scheduled. When calling this, don't hold any
 127  * locks that are also used by the callback. */
 128 void vhost_poll_flush(struct vhost_poll *poll)
 129 {
 130         vhost_work_flush(poll->dev, &poll->work);
 131 }
 132
 133 static inline void vhost_work_queue(struct vhost_dev *dev,
 134                                     struct vhost_work *work)
 135 {
 136         unsigned long flags;
 137
 138         spin_lock_irqsave(&dev->work_lock, flags);
 139         if (list_empty(&work->node)) {
 140                 list_add_tail(&work->node, &dev->work_list);
 141                 work->queue_seq++;
 142                 wake_up_process(dev->worker);
 143         }
 144         spin_unlock_irqrestore(&dev->work_lock, flags);
 145 }
 146
 147 void vhost_poll_queue(struct vhost_poll *poll)
 148 {
 149         vhost_work_queue(poll->dev, &poll->work);
 150 }
 151
 152 static void vhost_vq_reset(struct vhost_dev *dev,
 153                            struct vhost_virtqueue *vq)
 154 {
 155         vq->num = 1;
 156         vq->desc = NULL;
 157         vq->avail = NULL;
 158         vq->used = NULL;
 159         vq->last_avail_idx = 0;
 160         vq->avail_idx = 0;
 161         vq->last_used_idx = 0;
 162         vq->used_flags = 0;
 163         vq->log_used = false;
 164         vq->log_addr = -1ull;
 165         vq->vhost_hlen = 0;
 166         vq->sock_hlen = 0;
 167         vq->private_data = NULL;
 168         vq->log_base = NULL;
 169         vq->error_ctx = NULL;
 170         vq->error = NULL;
 171         vq->kick = NULL;
 172         vq->call_ctx = NULL;
 173         vq->call = NULL;
 174         vq->log_ctx = NULL;
 175 }
 176
 177 static int vhost_worker(void *data)
 178 {
 179         struct vhost_dev *dev = data;
 180         struct vhost_work *work = NULL;
 181         unsigned uninitialized_var(seq);
 182
 183         use_mm(dev->mm);
 184
 185         for (;;) {
 186                 /* mb paired w/ kthread_stop */
 187                 set_current_state(TASK_INTERRUPTIBLE);
 188
 189                 spin_lock_irq(&dev->work_lock);
 190                 if (work) {
 191                         work->done_seq = seq;
 192                         if (work->flushing)
 193                                 wake_up_all(&work->done);
 194                 }
 195
 196                 if (kthread_should_stop()) {
 197                         spin_unlock_irq(&dev->work_lock);
 198                         __set_current_state(TASK_RUNNING);
 199                         break;
 200                 }
 201                 if (!list_empty(&dev->work_list)) {
 202                         work = list_first_entry(&dev->work_list,
 203                                                 struct vhost_work, node);
 204                         list_del_init(&work->node);
 205                         seq = work->queue_seq;
 206                 } else
 207                         work = NULL;
 208                 spin_unlock_irq(&dev->work_lock);
 209
 210                 if (work) {
 211                         __set_current_state(TASK_RUNNING);
 212                         work->fn(work);
 213                 } else
 214                         schedule();
 215
 216         }
 217         unuse_mm(dev->mm);
 218         return 0;
 219 }
 220
 221 /* Helper to allocate iovec buffers for all vqs. */
 222 static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
 223 {
 224         int i;
 225         for (i = 0; i < dev->nvqs; ++i) {
 226                 dev->vqs[i].indirect = kmalloc(sizeof *dev->vqs[i].indirect *
 227                                                UIO_MAXIOV, GFP_KERNEL);
 228                 dev->vqs[i].log = kmalloc(sizeof *dev->vqs[i].log * UIO_MAXIOV,
 229                                           GFP_KERNEL);
 230                 dev->vqs[i].heads = kmalloc(sizeof *dev->vqs[i].heads *
 231                                             UIO_MAXIOV, GFP_KERNEL);
 232
 233                 if (!dev->vqs[i].indirect || !dev->vqs[i].log ||
 234                         !dev->vqs[i].heads)
 235                         goto err_nomem;
 236         }
 237         return 0;
 238 err_nomem:
 239         for (; i >= 0; --i) {
 240                 kfree(dev->vqs[i].indirect);
 241                 kfree(dev->vqs[i].log);
 242                 kfree(dev->vqs[i].heads);
 243         }
 244         return -ENOMEM;
 245 }
 246
 247 static void vhost_dev_free_iovecs(struct vhost_dev *dev)
 248 {
 249         int i;
 250         for (i = 0; i < dev->nvqs; ++i) {
 251                 kfree(dev->vqs[i].indirect);
 252                 dev->vqs[i].indirect = NULL;
 253                 kfree(dev->vqs[i].log);
 254                 dev->vqs[i].log = NULL;
 255                 kfree(dev->vqs[i].heads);
 256                 dev->vqs[i].heads = NULL;
 257         }
 258 }
 259
 260 long vhost_dev_init(struct vhost_dev *dev,
 261                     struct vhost_virtqueue *vqs, int nvqs)
 262 {
 263         int i;
 264
 265         dev->vqs = vqs;
 266         dev->nvqs = nvqs;
 267         mutex_init(&dev->mutex);
 268         dev->log_ctx = NULL;
 269         dev->log_file = NULL;
 270         dev->memory = NULL;
 271         dev->mm = NULL;
 272         spin_lock_init(&dev->work_lock);
 273         INIT_LIST_HEAD(&dev->work_list);
 274         dev->worker = NULL;
 275
 276         for (i = 0; i < dev->nvqs; ++i) {
 277                 dev->vqs[i].log = NULL;
 278                 dev->vqs[i].indirect = NULL;
 279                 dev->vqs[i].heads = NULL;
 280                 dev->vqs[i].dev = dev;
 281                 mutex_init(&dev->vqs[i].mutex);
 282                 vhost_vq_reset(dev, dev->vqs + i);
 283                 if (dev->vqs[i].handle_kick)
 284                         vhost_poll_init(&dev->vqs[i].poll,
 285                                         dev->vqs[i].handle_kick, POLLIN, dev);
 286         }
 287
 288         return 0;
 289 }
 290
 291 /* Caller should have device mutex */
 292 long vhost_dev_check_owner(struct vhost_dev *dev)
 293 {
 294         /* Are you the owner? If not, I don't think you mean to do that */
 295         return dev->mm == current->mm ? 0 : -EPERM;
 296 }
 297
 298 struct vhost_attach_cgroups_struct {
 299         struct vhost_work work;
 300         struct task_struct *owner;
 301         int ret;
 302 };
 303
 304 static void vhost_attach_cgroups_work(struct vhost_work *work)
 305 {
 306         struct vhost_attach_cgroups_struct *s;
 307         s = container_of(work, struct vhost_attach_cgroups_struct, work);
 308         s->ret = cgroup_attach_task_all(s->owner, current);
 309 }
 310
 311 static int vhost_attach_cgroups(struct vhost_dev *dev)
 312 {
 313         struct vhost_attach_cgroups_struct attach;
 314         attach.owner = current;
 315         vhost_work_init(&attach.work, vhost_attach_cgroups_work);
 316         vhost_work_queue(dev, &attach.work);
 317         vhost_work_flush(dev, &attach.work);
 318         return attach.ret;
 319 }
 320
 321 /* Caller should have device mutex */
 322 static long vhost_dev_set_owner(struct vhost_dev *dev)
 323 {
 324         struct task_struct *worker;
 325         int err;
 326         /* Is there an owner already? */
 327         if (dev->mm) {
 328                 err = -EBUSY;
 329                 goto err_mm;
 330         }
 331         /* No owner, become one */
 332         dev->mm = get_task_mm(current);
 333         worker = kthread_create(vhost_worker, dev, "vhost-%d", current->pid);
 334         if (IS_ERR(worker)) {
 335                 err = PTR_ERR(worker);
 336                 goto err_worker;
 337         }
 338
 339         dev->worker = worker;
 340         wake_up_process(worker);        /* avoid contributing to loadavg */
 341
 342         err = vhost_attach_cgroups(dev);
 343         if (err)
 344                 goto err_cgroup;
 345
 346         err = vhost_dev_alloc_iovecs(dev);
 347         if (err)
 348                 goto err_cgroup;
 349
 350         return 0;
 351 err_cgroup:
 352         kthread_stop(worker);
 353         dev->worker = NULL;
 354 err_worker:
 355         if (dev->mm)
 356                 mmput(dev->mm);
 357         dev->mm = NULL;
 358 err_mm:
 359         return err;
 360 }
 361
 362 /* Caller should have device mutex */
 363 long vhost_dev_reset_owner(struct vhost_dev *dev)
 364 {
 365         struct vhost_memory *memory;
 366
 367         /* Restore memory to default empty mapping. */
 368         memory = kmalloc(offsetof(struct vhost_memory, regions), GFP_KERNEL);
 369         if (!memory)
 370                 return -ENOMEM;
 371
 372         vhost_dev_cleanup(dev);
 373
 374         memory->nregions = 0;
 375         RCU_INIT_POINTER(dev->memory, memory);
 376         return 0;
 377 }
 378
 379 /* Caller should have device mutex */
 380 void vhost_dev_cleanup(struct vhost_dev *dev)
 381 {
 382         int i;
 383         for (i = 0; i < dev->nvqs; ++i) {
 384                 if (dev->vqs[i].kick && dev->vqs[i].handle_kick) {
 385                         vhost_poll_stop(&dev->vqs[i].poll);
 386                         vhost_poll_flush(&dev->vqs[i].poll);
 387                 }
 388                 if (dev->vqs[i].error_ctx)
 389                         eventfd_ctx_put(dev->vqs[i].error_ctx);
 390                 if (dev->vqs[i].error)
 391                         fput(dev->vqs[i].error);
 392                 if (dev->vqs[i].kick)
 393                         fput(dev->vqs[i].kick);
 394                 if (dev->vqs[i].call_ctx)
 395                         eventfd_ctx_put(dev->vqs[i].call_ctx);
 396                 if (dev->vqs[i].call)
 397                         fput(dev->vqs[i].call);
 398                 vhost_vq_reset(dev, dev->vqs + i);
 399         }
 400         vhost_dev_free_iovecs(dev);
 401         if (dev->log_ctx)
 402                 eventfd_ctx_put(dev->log_ctx);
 403         dev->log_ctx = NULL;
 404         if (dev->log_file)
 405                 fput(dev->log_file);
 406         dev->log_file = NULL;
 407         /* No one will access memory at this point */
 408         kfree(rcu_dereference_protected(dev->memory,
 409                                         lockdep_is_held(&dev->mutex)));
 410         RCU_INIT_POINTER(dev->memory, NULL);
 411         WARN_ON(!list_empty(&dev->work_list));
 412         if (dev->worker) {
 413                 kthread_stop(dev->worker);
 414                 dev->worker = NULL;
 415         }
 416         if (dev->mm)
 417                 mmput(dev->mm);
 418         dev->mm = NULL;
 419 }
 420
 421 static int log_access_ok(void __user *log_base, u64 addr, unsigned long sz)
 422 {
 423         u64 a = addr / VHOST_PAGE_SIZE / 8;
 424         /* Make sure 64 bit math will not overflow. */
 425         if (a > ULONG_MAX - (unsigned long)log_base ||
 426             a + (unsigned long)log_base > ULONG_MAX)
 427                 return 0;
 428
 429         return access_ok(VERIFY_WRITE, log_base + a,
 430                          (sz + VHOST_PAGE_SIZE * 8 - 1) / VHOST_PAGE_SIZE / 8);
 431 }
 432
 433 /* Caller should have vq mutex and device mutex. */
 434 static int vq_memory_access_ok(void __user *log_base, struct vhost_memory *mem,
 435                                int log_all)
 436 {
 437         int i;
 438
 439         if (!mem)
 440                 return 0;
 441
 442         for (i = 0; i < mem->nregions; ++i) {
 443                 struct vhost_memory_region *m = mem->regions + i;
 444                 unsigned long a = m->userspace_addr;
 445                 if (m->memory_size > ULONG_MAX)
 446                         return 0;
 447                 else if (!access_ok(VERIFY_WRITE, (void __user *)a,
 448                                     m->memory_size))
 449                         return 0;
 450                 else if (log_all && !log_access_ok(log_base,
 451                                                    m->guest_phys_addr,
 452                                                    m->memory_size))
 453                         return 0;
 454         }
 455         return 1;
 456 }
 457
 458 /* Can we switch to this memory table? */
 459 /* Caller should have device mutex but not vq mutex */
 460 static int memory_access_ok(struct vhost_dev *d, struct vhost_memory *mem,
 461                             int log_all)
 462 {
 463         int i;
 464         for (i = 0; i < d->nvqs; ++i) {
 465                 int ok;
 466                 mutex_lock(&d->vqs[i].mutex);
 467                 /* If ring is inactive, will check when it's enabled. */
 468                 if (d->vqs[i].private_data)
 469                         ok = vq_memory_access_ok(d->vqs[i].log_base, mem,
 470                                                  log_all);
 471                 else
 472                         ok = 1;
 473                 mutex_unlock(&d->vqs[i].mutex);
 474                 if (!ok)
 475                         return 0;
 476         }
 477         return 1;
 478 }
 479
 480 static int vq_access_ok(unsigned int num,
 481                         struct vring_desc __user *desc,
 482                         struct vring_avail __user *avail,
 483                         struct vring_used __user *used)
 484 {
 485         return access_ok(VERIFY_READ, desc, num * sizeof *desc) &&
 486                access_ok(VERIFY_READ, avail,
 487                          sizeof *avail + num * sizeof *avail->ring) &&
 488                access_ok(VERIFY_WRITE, used,
 489                         sizeof *used + num * sizeof *used->ring);
 490 }
 491
 492 /* Can we log writes? */
 493 /* Caller should have device mutex but not vq mutex */
 494 int vhost_log_access_ok(struct vhost_dev *dev)
 495 {
 496         struct vhost_memory *mp;
 497
 498         mp = rcu_dereference_protected(dev->memory,
 499                                        lockdep_is_held(&dev->mutex));
 500         return memory_access_ok(dev, mp, 1);
 501 }
 502
 503 /* Verify access for write logging. */
 504 /* Caller should have vq mutex and device mutex */
 505 static int vq_log_access_ok(struct vhost_virtqueue *vq, void __user *log_base)
 506 {
 507         struct vhost_memory *mp;
 508
 509         mp = rcu_dereference_protected(vq->dev->memory,
 510                                        lockdep_is_held(&vq->mutex));
 511         return vq_memory_access_ok(log_base, mp,
 512                             vhost_has_feature(vq->dev, VHOST_F_LOG_ALL)) &&
 513                 (!vq->log_used || log_access_ok(log_base, vq->log_addr,
 514                                         sizeof *vq->used +
 515                                         vq->num * sizeof *vq->used->ring));
 516 }
 517
 518 /* Can we start vq? */
 519 /* Caller should have vq mutex and device mutex */
 520 int vhost_vq_access_ok(struct vhost_virtqueue *vq)
 521 {
 522         return vq_access_ok(vq->num, vq->desc, vq->avail, vq->used) &&
 523                 vq_log_access_ok(vq, vq->log_base);
 524 }
 525
 526 static long vhost_set_memory(struct vhost_dev *d, struct vhost_memory __user *m)
 527 {
 528         struct vhost_memory mem, *newmem, *oldmem;
 529         unsigned long size = offsetof(struct vhost_memory, regions);
 530         if (copy_from_user(&mem, m, size))
 531                 return -EFAULT;
 532         if (mem.padding)
 533                 return -EOPNOTSUPP;
 534         if (mem.nregions > VHOST_MEMORY_MAX_NREGIONS)
 535                 return -E2BIG;
 536         newmem = kmalloc(size + mem.nregions * sizeof *m->regions, GFP_KERNEL);
 537         if (!newmem)
 538                 return -ENOMEM;
 539
 540         memcpy(newmem, &mem, size);
 541         if (copy_from_user(newmem->regions, m->regions,
 542                            mem.nregions * sizeof *m->regions)) {
 543                 kfree(newmem);
 544                 return -EFAULT;
 545         }
 546
 547         if (!memory_access_ok(d, newmem, vhost_has_feature(d, VHOST_F_LOG_ALL))) {
 548                 kfree(newmem);
 549                 return -EFAULT;
 550         }
 551         oldmem = rcu_dereference_protected(d->memory,
 552                                            lockdep_is_held(&d->mutex));
 553         rcu_assign_pointer(d->memory, newmem);
 554         synchronize_rcu();
 555         kfree(oldmem);
 556         return 0;
 557 }
 558
 559 static int init_used(struct vhost_virtqueue *vq,
 560                      struct vring_used __user *used)
 561 {
 562         int r = put_user(vq->used_flags, &used->flags);
 563         if (r)
 564                 return r;
 565         return get_user(vq->last_used_idx, &used->idx);
 566 }
 567
 568 static long vhost_set_vring(struct vhost_dev *d, int ioctl, void __user *argp)
 569 {
 570         struct file *eventfp, *filep = NULL,
 571                     *pollstart = NULL, *pollstop = NULL;
 572         struct eventfd_ctx *ctx = NULL;
 573         u32 __user *idxp = argp;
 574         struct vhost_virtqueue *vq;
 575         struct vhost_vring_state s;
 576         struct vhost_vring_file f;
 577         struct vhost_vring_addr a;
 578         u32 idx;
 579         long r;
 580
 581         r = get_user(idx, idxp);
 582         if (r < 0)
 583                 return r;
 584         if (idx >= d->nvqs)
 585                 return -ENOBUFS;
 586
 587         vq = d->vqs + idx;
 588
 589         mutex_lock(&vq->mutex);
 590
 591         switch (ioctl) {
 592         case VHOST_SET_VRING_NUM:
 593                 /* Resizing ring with an active backend?
 594                  * You don't want to do that. */
 595                 if (vq->private_data) {
 596                         r = -EBUSY;
 597                         break;
 598                 }
 599                 if (copy_from_user(&s, argp, sizeof s)) {
 600                         r = -EFAULT;
 601                         break;
 602                 }
 603                 if (!s.num || s.num > 0xffff || (s.num & (s.num - 1))) {
 604                         r = -EINVAL;
 605                         break;
 606                 }
 607                 vq->num = s.num;
 608                 break;
 609         case VHOST_SET_VRING_BASE:
 610                 /* Moving base with an active backend?
 611                  * You don't want to do that. */
 612                 if (vq->private_data) {
 613                         r = -EBUSY;
 614                         break;
 615                 }
 616                 if (copy_from_user(&s, argp, sizeof s)) {
 617                         r = -EFAULT;
 618                         break;
 619                 }
 620                 if (s.num > 0xffff) {
 621                         r = -EINVAL;
 622                         break;
 623                 }
 624                 vq->last_avail_idx = s.num;
 625                 /* Forget the cached index value. */
 626                 vq->avail_idx = vq->last_avail_idx;
 627                 break;
 628         case VHOST_GET_VRING_BASE:
 629                 s.index = idx;
 630                 s.num = vq->last_avail_idx;
 631                 if (copy_to_user(argp, &s, sizeof s))
 632                         r = -EFAULT;
 633                 break;
 634         case VHOST_SET_VRING_ADDR:
 635                 if (copy_from_user(&a, argp, sizeof a)) {
 636                         r = -EFAULT;
 637                         break;
 638                 }
 639                 if (a.flags & ~(0x1 << VHOST_VRING_F_LOG)) {
 640                         r = -EOPNOTSUPP;
 641                         break;
 642                 }
 643                 /* For 32bit, verify that the top 32bits of the user
 644                    data are set to zero. */
 645                 if ((u64)(unsigned long)a.desc_user_addr != a.desc_user_addr ||
 646                     (u64)(unsigned long)a.used_user_addr != a.used_user_addr ||
 647                     (u64)(unsigned long)a.avail_user_addr != a.avail_user_addr) {
 648                         r = -EFAULT;
 649                         break;
 650                 }
 651                 if ((a.avail_user_addr & (sizeof *vq->avail->ring - 1)) ||
 652                     (a.used_user_addr & (sizeof *vq->used->ring - 1)) ||
 653                     (a.log_guest_addr & (sizeof *vq->used->ring - 1))) {
 654                         r = -EINVAL;
 655                         break;
 656                 }
 657
 658                 /* We only verify access here if backend is configured.
 659                  * If it is not, we don't as size might not have been setup.
 660                  * We will verify when backend is configured. */
 661                 if (vq->private_data) {
 662                         if (!vq_access_ok(vq->num,
 663                                 (void __user *)(unsigned long)a.desc_user_addr,
 664                                 (void __user *)(unsigned long)a.avail_user_addr,
 665                                 (void __user *)(unsigned long)a.used_user_addr)) {
 666                                 r = -EINVAL;
 667                                 break;
 668                         }
 669
 670                         /* Also validate log access for used ring if enabled. */
 671                         if ((a.flags & (0x1 << VHOST_VRING_F_LOG)) &&
 672                             !log_access_ok(vq->log_base, a.log_guest_addr,
 673                                            sizeof *vq->used +
 674                                            vq->num * sizeof *vq->used->ring)) {
 675                                 r = -EINVAL;
 676                                 break;
 677                         }
 678                 }
 679
 680                 r = init_used(vq, (struct vring_used __user *)(unsigned long)
 681                               a.used_user_addr);
 682                 if (r)
 683                         break;
 684                 vq->log_used = !!(a.flags & (0x1 << VHOST_VRING_F_LOG));
 685                 vq->desc = (void __user *)(unsigned long)a.desc_user_addr;
 686                 vq->avail = (void __user *)(unsigned long)a.avail_user_addr;
 687                 vq->log_addr = a.log_guest_addr;
 688                 vq->used = (void __user *)(unsigned long)a.used_user_addr;
 689                 break;
 690         case VHOST_SET_VRING_KICK:
 691                 if (copy_from_user(&f, argp, sizeof f)) {
 692                         r = -EFAULT;
 693                         break;
 694                 }
 695                 eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
 696                 if (IS_ERR(eventfp)) {
 697                         r = PTR_ERR(eventfp);
 698                         break;
 699                 }
 700                 if (eventfp != vq->kick) {
 701                         pollstop = filep = vq->kick;
 702                         pollstart = vq->kick = eventfp;
 703                 } else
 704                         filep = eventfp;
 705                 break;
 706         case VHOST_SET_VRING_CALL:
 707                 if (copy_from_user(&f, argp, sizeof f)) {
 708                         r = -EFAULT;
 709                         break;
 710                 }
 711                 eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
 712                 if (IS_ERR(eventfp)) {
 713                         r = PTR_ERR(eventfp);
 714                         break;
 715                 }
 716                 if (eventfp != vq->call) {
 717                         filep = vq->call;
 718                         ctx = vq->call_ctx;
 719                         vq->call = eventfp;
 720                         vq->call_ctx = eventfp ?
 721                                 eventfd_ctx_fileget(eventfp) : NULL;
 722                 } else
 723                         filep = eventfp;
 724                 break;
 725         case VHOST_SET_VRING_ERR:
 726                 if (copy_from_user(&f, argp, sizeof f)) {
 727                         r = -EFAULT;
 728                         break;
 729                 }
 730                 eventfp = f.fd == -1 ? NULL : eventfd_fget(f.fd);
 731                 if (IS_ERR(eventfp)) {
 732                         r = PTR_ERR(eventfp);
 733                         break;
 734                 }
 735                 if (eventfp != vq->error) {
 736                         filep = vq->error;
 737                         vq->error = eventfp;
 738                         ctx = vq->error_ctx;
 739                         vq->error_ctx = eventfp ?
 740                                 eventfd_ctx_fileget(eventfp) : NULL;
 741                 } else
 742                         filep = eventfp;
 743                 break;
 744         default:
 745                 r = -ENOIOCTLCMD;
 746         }
 747
 748         if (pollstop && vq->handle_kick)
 749                 vhost_poll_stop(&vq->poll);
 750
 751         if (ctx)
 752                 eventfd_ctx_put(ctx);
 753         if (filep)
 754                 fput(filep);
 755
 756         if (pollstart && vq->handle_kick)
 757                 vhost_poll_start(&vq->poll, vq->kick);
 758
 759         mutex_unlock(&vq->mutex);
 760
 761         if (pollstop && vq->handle_kick)
 762                 vhost_poll_flush(&vq->poll);
 763         return r;
 764 }
 765
 766 /* Caller must have device mutex */
 767 long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, unsigned long arg)
 768 {
 769         void __user *argp = (void __user *)arg;
 770         struct file *eventfp, *filep = NULL;
 771         struct eventfd_ctx *ctx = NULL;
 772         u64 p;
 773         long r;
 774         int i, fd;
 775
 776         /* If you are not the owner, you can become one */
 777         if (ioctl == VHOST_SET_OWNER) {
 778                 r = vhost_dev_set_owner(d);
 779                 goto done;
 780         }
 781
 782         /* You must be the owner to do anything else */
 783         r = vhost_dev_check_owner(d);
 784         if (r)
 785                 goto done;
 786
 787         switch (ioctl) {
 788         case VHOST_SET_MEM_TABLE:
 789                 r = vhost_set_memory(d, argp);
 790                 break;
 791         case VHOST_SET_LOG_BASE:
 792                 if (copy_from_user(&p, argp, sizeof p)) {
 793                         r = -EFAULT;
 794                         break;
 795                 }
 796                 if ((u64)(unsigned long)p != p) {
 797                         r = -EFAULT;
 798                         break;
 799                 }
 800                 for (i = 0; i < d->nvqs; ++i) {
 801                         struct vhost_virtqueue *vq;
 802                         void __user *base = (void __user *)(unsigned long)p;
 803                         vq = d->vqs + i;
 804                         mutex_lock(&vq->mutex);
 805                         /* If ring is inactive, will check when it's enabled. */
 806                         if (vq->private_data && !vq_log_access_ok(vq, base))
 807                                 r = -EFAULT;
 808                         else
 809                                 vq->log_base = base;
 810                         mutex_unlock(&vq->mutex);
 811                 }
 812                 break;
 813         case VHOST_SET_LOG_FD:
 814                 r = get_user(fd, (int __user *)argp);
 815                 if (r < 0)
 816                         break;
 817                 eventfp = fd == -1 ? NULL : eventfd_fget(fd);
 818                 if (IS_ERR(eventfp)) {
 819                         r = PTR_ERR(eventfp);
 820                         break;
 821                 }
 822                 if (eventfp != d->log_file) {
 823                         filep = d->log_file;
 824                         ctx = d->log_ctx;
 825                         d->log_ctx = eventfp ?
 826                                 eventfd_ctx_fileget(eventfp) : NULL;
 827                 } else
 828                         filep = eventfp;
 829                 for (i = 0; i < d->nvqs; ++i) {
 830                         mutex_lock(&d->vqs[i].mutex);
 831                         d->vqs[i].log_ctx = d->log_ctx;
 832                         mutex_unlock(&d->vqs[i].mutex);
 833                 }
 834                 if (ctx)
 835                         eventfd_ctx_put(ctx);
 836                 if (filep)
 837                         fput(filep);
 838                 break;
 839         default:
 840                 r = vhost_set_vring(d, ioctl, argp);
 841                 break;
 842         }
 843 done:
 844         return r;
 845 }
 846
 847 static const struct vhost_memory_region *find_region(struct vhost_memory *mem,
 848                                                      __u64 addr, __u32 len)
 849 {
 850         struct vhost_memory_region *reg;
 851         int i;
 852         /* linear search is not brilliant, but we really have on the order of 6
 853          * regions in practice */
 854         for (i = 0; i < mem->nregions; ++i) {
 855                 reg = mem->regions + i;
 856                 if (reg->guest_phys_addr <= addr &&
 857                     reg->guest_phys_addr + reg->memory_size - 1 >= addr)
 858                         return reg;
 859         }
 860         return NULL;
 861 }
 862
 863 /* TODO: This is really inefficient.  We need something like get_user()
 864  * (instruction directly accesses the data, with an exception table entry
 865  * returning -EFAULT). See Documentation/x86/exception-tables.txt.
 866  */
 867 static int set_bit_to_user(int nr, void __user *addr)
 868 {
 869         unsigned long log = (unsigned long)addr;
 870         struct page *page;
 871         void *base;
 872         int bit = nr + (log % PAGE_SIZE) * 8;
 873         int r;
 874         r = get_user_pages_fast(log, 1, 1, &page);
 875         if (r < 0)
 876                 return r;
 877         BUG_ON(r != 1);
 878         base = kmap_atomic(page, KM_USER0);
 879         set_bit(bit, base);
 880         kunmap_atomic(base, KM_USER0);
 881         set_page_dirty_lock(page);
 882         put_page(page);
 883         return 0;
 884 }
 885
 886 static int log_write(void __user *log_base,
 887                      u64 write_address, u64 write_length)
 888 {
 889         u64 write_page = write_address / VHOST_PAGE_SIZE;
 890         int r;
 891         if (!write_length)
 892                 return 0;
 893         write_length += write_address % VHOST_PAGE_SIZE;
 894         for (;;) {
 895                 u64 base = (u64)(unsigned long)log_base;
 896                 u64 log = base + write_page / 8;
 897                 int bit = write_page % 8;
 898                 if ((u64)(unsigned long)log != log)
 899                         return -EFAULT;
 900                 r = set_bit_to_user(bit, (void __user *)(unsigned long)log);
 901                 if (r < 0)
 902                         return r;
 903                 if (write_length <= VHOST_PAGE_SIZE)
 904                         break;
 905                 write_length -= VHOST_PAGE_SIZE;
 906                 write_page += 1;
 907         }
 908         return r;
 909 }
 910
 911 int vhost_log_write(struct vhost_virtqueue *vq, struct vhost_log *log,
 912                     unsigned int log_num, u64 len)
 913 {
 914         int i, r;
 915
 916         /* Make sure data written is seen before log. */
 917         smp_wmb();
 918         for (i = 0; i < log_num; ++i) {
 919                 u64 l = min(log[i].len, len);
 920                 r = log_write(vq->log_base, log[i].addr, l);
 921                 if (r < 0)
 922                         return r;
 923                 len -= l;
 924                 if (!len) {
 925                         if (vq->log_ctx)
 926                                 eventfd_signal(vq->log_ctx, 1);
 927                         return 0;
 928                 }
 929         }
 930         /* Length written exceeds what we have stored. This is a bug. */
 931         BUG();
 932         return 0;
 933 }
 934
 935 static int translate_desc(struct vhost_dev *dev, u64 addr, u32 len,
 936                           struct iovec iov[], int iov_size)
 937 {
 938         const struct vhost_memory_region *reg;
 939         struct vhost_memory *mem;
 940         struct iovec *_iov;
 941         u64 s = 0;
 942         int ret = 0;
 943
 944         rcu_read_lock();
 945
 946         mem = rcu_dereference(dev->memory);
 947         while ((u64)len > s) {
 948                 u64 size;
 949                 if (unlikely(ret >= iov_size)) {
 950                         ret = -ENOBUFS;
 951                         break;
 952                 }
 953                 reg = find_region(mem, addr, len);
 954                 if (unlikely(!reg)) {
 955                         ret = -EFAULT;
 956                         break;
 957                 }
 958                 _iov = iov + ret;
 959                 size = reg->memory_size - addr + reg->guest_phys_addr;
 960                 _iov->iov_len = min((u64)len, size);
 961                 _iov->iov_base = (void __user *)(unsigned long)
 962                         (reg->userspace_addr + addr - reg->guest_phys_addr);
 963                 s += size;
 964                 addr += size;
 965                 ++ret;
 966         }
 967
 968         rcu_read_unlock();
 969         return ret;
 970 }
 971
 972 /* Each buffer in the virtqueues is actually a chain of descriptors.  This
 973  * function returns the next descriptor in the chain,
 974  * or -1U if we're at the end. */
 975 static unsigned next_desc(struct vring_desc *desc)
 976 {
 977         unsigned int next;
 978
 979         /* If this descriptor says it doesn't chain, we're done. */
 980         if (!(desc->flags & VRING_DESC_F_NEXT))
 981                 return -1U;
 982
 983         /* Check they're not leading us off end of descriptors. */
 984         next = desc->next;
 985         /* Make sure compiler knows to grab that: we don't want it changing! */
 986         /* We will use the result as an index in an array, so most
 987          * architectures only need a compiler barrier here. */
 988         read_barrier_depends();
 989
 990         return next;
 991 }
 992
 993 static int get_indirect(struct vhost_dev *dev, struct vhost_virtqueue *vq,
 994                         struct iovec iov[], unsigned int iov_size,
 995                         unsigned int *out_num, unsigned int *in_num,
 996                         struct vhost_log *log, unsigned int *log_num,
 997                         struct vring_desc *indirect)
 998 {
 999         struct vring_desc desc;
1000         unsigned int i = 0, count, found = 0;
1001         int ret;
1002
1003         /* Sanity check */
1004         if (unlikely(indirect->len % sizeof desc)) {
1005                 vq_err(vq, "Invalid length in indirect descriptor: "
1006                        "len 0x%llx not multiple of 0x%zx\n",
1007                        (unsigned long long)indirect->len,
1008                        sizeof desc);
1009                 return -EINVAL;
1010         }
1011
1012         ret = translate_desc(dev, indirect->addr, indirect->len, vq->indirect,
1013                              UIO_MAXIOV);
1014         if (unlikely(ret < 0)) {
1015                 vq_err(vq, "Translation failure %d in indirect.\n", ret);
1016                 return ret;
1017         }
1018
1019         /* We will use the result as an address to read from, so most
1020          * architectures only need a compiler barrier here. */
1021         read_barrier_depends();
1022
1023         count = indirect->len / sizeof desc;
1024         /* Buffers are chained via a 16 bit next field, so
1025          * we can have at most 2^16 of these. */
1026         if (unlikely(count > USHRT_MAX + 1)) {
1027                 vq_err(vq, "Indirect buffer length too big: %d\n",
1028                        indirect->len);
1029                 return -E2BIG;
1030         }
1031
1032         do {
1033                 unsigned iov_count = *in_num + *out_num;
1034                 if (unlikely(++found > count)) {
1035                         vq_err(vq, "Loop detected: last one at %u "
1036                                "indirect size %u\n",
1037                                i, count);
1038                         return -EINVAL;
1039                 }
1040                 if (unlikely(memcpy_fromiovec((unsigned char *)&desc, vq->indirect,
1041                                               sizeof desc))) {
1042                         vq_err(vq, "Failed indirect descriptor: idx %d, %zx\n",
1043                                i, (size_t)indirect->addr + i * sizeof desc);
1044                         return -EINVAL;
1045                 }
1046                 if (unlikely(desc.flags & VRING_DESC_F_INDIRECT)) {
1047                         vq_err(vq, "Nested indirect descriptor: idx %d, %zx\n",
1048                                i, (size_t)indirect->addr + i * sizeof desc);
1049                         return -EINVAL;
1050                 }
1051
1052                 ret = translate_desc(dev, desc.addr, desc.len, iov + iov_count,
1053                                      iov_size - iov_count);
1054                 if (unlikely(ret < 0)) {
1055                         vq_err(vq, "Translation failure %d indirect idx %d\n",
1056                                ret, i);
1057                         return ret;
1058                 }
1059                 /* If this is an input descriptor, increment that count. */
1060                 if (desc.flags & VRING_DESC_F_WRITE) {
1061                         *in_num += ret;
1062                         if (unlikely(log)) {
1063                                 log[*log_num].addr = desc.addr;
1064                                 log[*log_num].len = desc.len;
1065                                 ++*log_num;
1066                         }
1067                 } else {
1068                         /* If it's an output descriptor, they're all supposed
1069                          * to come before any input descriptors. */
1070                         if (unlikely(*in_num)) {
1071                                 vq_err(vq, "Indirect descriptor "
1072                                        "has out after in: idx %d\n", i);
1073                                 return -EINVAL;
1074                         }
1075                         *out_num += ret;
1076                 }
1077         } while ((i = next_desc(&desc)) != -1);
1078         return 0;
1079 }
1080
1081 /* This looks in the virtqueue and for the first available buffer, and converts
1082  * it to an iovec for convenient access.  Since descriptors consist of some
1083  * number of output then some number of input descriptors, it's actually two
1084  * iovecs, but we pack them into one and note how many of each there were.
1085  *
1086  * This function returns the descriptor number found, or vq->num (which is
1087  * never a valid descriptor number) if none was found.  A negative code is
1088  * returned on error. */
1089 int vhost_get_vq_desc(struct vhost_dev *dev, struct vhost_virtqueue *vq,
1090                       struct iovec iov[], unsigned int iov_size,
1091                       unsigned int *out_num, unsigned int *in_num,
1092                       struct vhost_log *log, unsigned int *log_num)
1093 {
1094         struct vring_desc desc;
1095         unsigned int i, head, found = 0;
1096         u16 last_avail_idx;
1097         int ret;
1098
1099         /* Check it isn't doing very strange things with descriptor numbers. */
1100         last_avail_idx = vq->last_avail_idx;
1101         if (unlikely(__get_user(vq->avail_idx, &vq->avail->idx))) {
1102                 vq_err(vq, "Failed to access avail idx at %p\n",
1103                        &vq->avail->idx);
1104                 return -EFAULT;
1105         }
1106
1107         if (unlikely((u16)(vq->avail_idx - last_avail_idx) > vq->num)) {
1108                 vq_err(vq, "Guest moved used index from %u to %u",
1109                        last_avail_idx, vq->avail_idx);
1110                 return -EFAULT;
1111         }
1112
1113         /* If there's nothing new since last we looked, return invalid. */
1114         if (vq->avail_idx == last_avail_idx)
1115                 return vq->num;
1116
1117         /* Only get avail ring entries after they have been exposed by guest. */
1118         smp_rmb();
1119
1120         /* Grab the next descriptor number they're advertising, and increment
1121          * the index we've seen. */
1122         if (unlikely(__get_user(head,
1123                                 &vq->avail->ring[last_avail_idx % vq->num]))) {
1124                 vq_err(vq, "Failed to read head: idx %d address %p\n",
1125                        last_avail_idx,
1126                        &vq->avail->ring[last_avail_idx % vq->num]);
1127                 return -EFAULT;
1128         }
1129
1130         /* If their number is silly, that's an error. */
1131         if (unlikely(head >= vq->num)) {
1132                 vq_err(vq, "Guest says index %u > %u is available",
1133                        head, vq->num);
1134                 return -EINVAL;
1135         }
1136
1137         /* When we start there are none of either input nor output. */
1138         *out_num = *in_num = 0;
1139         if (unlikely(log))
1140                 *log_num = 0;
1141
1142         i = head;
1143         do {
1144                 unsigned iov_count = *in_num + *out_num;
1145                 if (unlikely(i >= vq->num)) {
1146                         vq_err(vq, "Desc index is %u > %u, head = %u",
1147                                i, vq->num, head);
1148                         return -EINVAL;
1149                 }
1150                 if (unlikely(++found > vq->num)) {
1151                         vq_err(vq, "Loop detected: last one at %u "
1152                                "vq size %u head %u\n",
1153                                i, vq->num, head);
1154                         return -EINVAL;
1155                 }
1156                 ret = copy_from_user(&desc, vq->desc + i, sizeof desc);
1157                 if (unlikely(ret)) {
1158                         vq_err(vq, "Failed to get descriptor: idx %d addr %p\n",
1159                                i, vq->desc + i);
1160                         return -EFAULT;
1161                 }
1162                 if (desc.flags & VRING_DESC_F_INDIRECT) {
1163                         ret = get_indirect(dev, vq, iov, iov_size,
1164                                            out_num, in_num,
1165                                            log, log_num, &desc);
1166                         if (unlikely(ret < 0)) {
1167                                 vq_err(vq, "Failure detected "
1168                                        "in indirect descriptor at idx %d\n", i);
1169                                 return ret;
1170                         }
1171                         continue;
1172                 }
1173
1174                 ret = translate_desc(dev, desc.addr, desc.len, iov + iov_count,
1175                                      iov_size - iov_count);
1176                 if (unlikely(ret < 0)) {
1177                         vq_err(vq, "Translation failure %d descriptor idx %d\n",
1178                                ret, i);
1179                         return ret;
1180                 }
1181                 if (desc.flags & VRING_DESC_F_WRITE) {
1182                         /* If this is an input descriptor,
1183                          * increment that count. */
1184                         *in_num += ret;
1185                         if (unlikely(log)) {
1186                                 log[*log_num].addr = desc.addr;
1187                                 log[*log_num].len = desc.len;
1188                                 ++*log_num;
1189                         }
1190                 } else {
1191                         /* If it's an output descriptor, they're all supposed
1192                          * to come before any input descriptors. */
1193                         if (unlikely(*in_num)) {
1194                                 vq_err(vq, "Descriptor has out after in: "
1195                                        "idx %d\n", i);
1196                                 return -EINVAL;
1197                         }
1198                         *out_num += ret;
1199                 }
1200         } while ((i = next_desc(&desc)) != -1);
1201
1202         /* On success, increment avail index. */
1203         vq->last_avail_idx++;
1204         return head;
1205 }
1206
1207 /* Reverse the effect of vhost_get_vq_desc. Useful for error handling. */
1208 void vhost_discard_vq_desc(struct vhost_virtqueue *vq, int n)
1209 {
1210         vq->last_avail_idx -= n;
1211 }
1212
1213 /* After we've used one of their buffers, we tell them about it.  We'll then
1214  * want to notify the guest, using eventfd. */
1215 int vhost_add_used(struct vhost_virtqueue *vq, unsigned int head, int len)
1216 {
1217         struct vring_used_elem __user *used;
1218
1219         /* The virtqueue contains a ring of used buffers.  Get a pointer to the
1220          * next entry in that used ring. */
1221         used = &vq->used->ring[vq->last_used_idx % vq->num];
1222         if (__put_user(head, &used->id)) {
1223                 vq_err(vq, "Failed to write used id");
1224                 return -EFAULT;
1225         }
1226         if (__put_user(len, &used->len)) {
1227                 vq_err(vq, "Failed to write used len");
1228                 return -EFAULT;
1229         }
1230         /* Make sure buffer is written before we update index. */
1231         smp_wmb();
1232         if (__put_user(vq->last_used_idx + 1, &vq->used->idx)) {
1233                 vq_err(vq, "Failed to increment used idx");
1234                 return -EFAULT;
1235         }
1236         if (unlikely(vq->log_used)) {
1237                 /* Make sure data is seen before log. */
1238                 smp_wmb();
1239                 /* Log used ring entry write. */
1240                 log_write(vq->log_base,
1241                           vq->log_addr +
1242                            ((void __user *)used - (void __user *)vq->used),
1243                           sizeof *used);
1244                 /* Log used index update. */
1245                 log_write(vq->log_base,
1246                           vq->log_addr + offsetof(struct vring_used, idx),
1247                           sizeof vq->used->idx);
1248                 if (vq->log_ctx)
1249                         eventfd_signal(vq->log_ctx, 1);
1250         }
1251         vq->last_used_idx++;
1252         return 0;
1253 }
1254
1255 static int __vhost_add_used_n(struct vhost_virtqueue *vq,
1256                             struct vring_used_elem *heads,
1257                             unsigned count)
1258 {
1259         struct vring_used_elem __user *used;
1260         int start;
1261
1262         start = vq->last_used_idx % vq->num;
1263         used = vq->used->ring + start;
1264         if (__copy_to_user(used, heads, count * sizeof *used)) {
1265                 vq_err(vq, "Failed to write used");
1266                 return -EFAULT;
1267         }
1268         if (unlikely(vq->log_used)) {
1269                 /* Make sure data is seen before log. */
1270                 smp_wmb();
1271                 /* Log used ring entry write. */
1272                 log_write(vq->log_base,
1273                           vq->log_addr +
1274                            ((void __user *)used - (void __user *)vq->used),
1275                           count * sizeof *used);
1276         }
1277         vq->last_used_idx += count;
1278         return 0;
1279 }
1280
1281 /* After we've used one of their buffers, we tell them about it.  We'll then
1282  * want to notify the guest, using eventfd. */
1283 int vhost_add_used_n(struct vhost_virtqueue *vq, struct vring_used_elem *heads,
1284                      unsigned count)
1285 {
1286         int start, n, r;
1287
1288         start = vq->last_used_idx % vq->num;
1289         n = vq->num - start;
1290         if (n < count) {
1291                 r = __vhost_add_used_n(vq, heads, n);
1292                 if (r < 0)
1293                         return r;
1294                 heads += n;
1295                 count -= n;
1296         }
1297         r = __vhost_add_used_n(vq, heads, count);
1298
1299         /* Make sure buffer is written before we update index. */
1300         smp_wmb();
1301         if (put_user(vq->last_used_idx, &vq->used->idx)) {
1302                 vq_err(vq, "Failed to increment used idx");
1303                 return -EFAULT;
1304         }
1305         if (unlikely(vq->log_used)) {
1306                 /* Log used index update. */
1307                 log_write(vq->log_base,
1308                           vq->log_addr + offsetof(struct vring_used, idx),
1309                           sizeof vq->used->idx);
1310                 if (vq->log_ctx)
1311                         eventfd_signal(vq->log_ctx, 1);
1312         }
1313         return r;
1314 }
1315
1316 /* This actually signals the guest, using eventfd. */
1317 void vhost_signal(struct vhost_dev *dev, struct vhost_virtqueue *vq)
1318 {
1319         __u16 flags;
1320         /* Flush out used index updates. This is paired
1321          * with the barrier that the Guest executes when enabling
1322          * interrupts. */
1323         smp_mb();
1324
1325         if (__get_user(flags, &vq->avail->flags)) {
1326                 vq_err(vq, "Failed to get flags");
1327                 return;
1328         }
1329
1330         /* If they don't want an interrupt, don't signal, unless empty. */
1331         if ((flags & VRING_AVAIL_F_NO_INTERRUPT) &&
1332             (vq->avail_idx != vq->last_avail_idx ||
1333              !vhost_has_feature(dev, VIRTIO_F_NOTIFY_ON_EMPTY)))
1334                 return;
1335
1336         /* Signal the Guest tell them we used something up. */
1337         if (vq->call_ctx)
1338                 eventfd_signal(vq->call_ctx, 1);
1339 }
1340
1341 /* And here's the combo meal deal.  Supersize me! */
1342 void vhost_add_used_and_signal(struct vhost_dev *dev,
1343                                struct vhost_virtqueue *vq,
1344                                unsigned int head, int len)
1345 {
1346         vhost_add_used(vq, head, len);
1347         vhost_signal(dev, vq);
1348 }
1349
1350 /* multi-buffer version of vhost_add_used_and_signal */
1351 void vhost_add_used_and_signal_n(struct vhost_dev *dev,
1352                                  struct vhost_virtqueue *vq,
1353                                  struct vring_used_elem *heads, unsigned count)
1354 {
1355         vhost_add_used_n(vq, heads, count);
1356         vhost_signal(dev, vq);
1357 }
1358
1359 /* OK, now we need to know about added descriptors. */
1360 bool vhost_enable_notify(struct vhost_virtqueue *vq)
1361 {
1362         u16 avail_idx;
1363         int r;
1364         if (!(vq->used_flags & VRING_USED_F_NO_NOTIFY))
1365                 return false;
1366         vq->used_flags &= ~VRING_USED_F_NO_NOTIFY;
1367         r = put_user(vq->used_flags, &vq->used->flags);
1368         if (r) {
1369                 vq_err(vq, "Failed to enable notification at %p: %d\n",
1370                        &vq->used->flags, r);
1371                 return false;
1372         }
1373         /* They could have slipped one in as we were doing that: make
1374          * sure it's written, then check again. */
1375         smp_mb();
1376         r = __get_user(avail_idx, &vq->avail->idx);
1377         if (r) {
1378                 vq_err(vq, "Failed to check avail idx at %p: %d\n",
1379                        &vq->avail->idx, r);
1380                 return false;
1381         }
1382
1383         return avail_idx != vq->avail_idx;
1384 }
1385
1386 /* We don't need to be notified again. */
1387 void vhost_disable_notify(struct vhost_virtqueue *vq)
1388 {
1389         int r;
1390         if (vq->used_flags & VRING_USED_F_NO_NOTIFY)
1391                 return;
1392         vq->used_flags |= VRING_USED_F_NO_NOTIFY;
1393         r = put_user(vq->used_flags, &vq->used->flags);
1394         if (r)
1395                 vq_err(vq, "Failed to enable notification at %p: %d\n",
1396                        &vq->used->flags, r);
1397 }