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