drivers/vhost/vhost.c

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