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