vhost: correctly set bits of dirty pages
[linux-2.6.git] / 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         int r;
886         if (!write_length)
887                 return 0;
888         write_length += write_address % VHOST_PAGE_SIZE;
889         write_address /= VHOST_PAGE_SIZE;
890         for (;;) {
891                 u64 base = (u64)(unsigned long)log_base;
892                 u64 log = base + write_address / 8;
893                 int bit = write_address % 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_address += 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 }