1 /*
2  * vhost shadow virtqueue
3  *
4  * SPDX-FileCopyrightText: Red Hat, Inc. 2021
5  * SPDX-FileContributor: Author: Eugenio Pérez <eperezma@redhat.com>
6  *
7  * SPDX-License-Identifier: GPL-2.0-or-later
8  */
9 
10 #include "qemu/osdep.h"
11 #include "hw/virtio/vhost-shadow-virtqueue.h"
12 
13 #include "qemu/error-report.h"
14 #include "qapi/error.h"
15 #include "qemu/main-loop.h"
16 #include "qemu/log.h"
17 #include "qemu/memalign.h"
18 #include "linux-headers/linux/vhost.h"
19 
20 /**
21  * Validate the transport device features that both guests can use with the SVQ
22  * and SVQs can use with the device.
23  *
24  * @dev_features: The features
25  * @errp: Error pointer
26  */
27 bool vhost_svq_valid_features(uint64_t features, Error **errp)
28 {
29     bool ok = true;
30     uint64_t svq_features = features;
31 
32     for (uint64_t b = VIRTIO_TRANSPORT_F_START; b <= VIRTIO_TRANSPORT_F_END;
33          ++b) {
34         switch (b) {
35         case VIRTIO_F_ANY_LAYOUT:
36         case VIRTIO_RING_F_EVENT_IDX:
37             continue;
38 
39         case VIRTIO_F_ACCESS_PLATFORM:
40             /* SVQ trust in the host's IOMMU to translate addresses */
41         case VIRTIO_F_VERSION_1:
42             /* SVQ trust that the guest vring is little endian */
43             if (!(svq_features & BIT_ULL(b))) {
44                 svq_features |= BIT_ULL(b);
45                 ok = false;
46             }
47             continue;
48 
49         default:
50             if (svq_features & BIT_ULL(b)) {
51                 svq_features &= ~BIT_ULL(b);
52                 ok = false;
53             }
54         }
55     }
56 
57     if (!ok) {
58         error_setg(errp, "SVQ Invalid device feature flags, offer: 0x%"PRIx64
59                          ", ok: 0x%"PRIx64, features, svq_features);
60     }
61     return ok;
62 }
63 
64 /**
65  * Number of descriptors that the SVQ can make available from the guest.
66  *
67  * @svq: The svq
68  */
69 static uint16_t vhost_svq_available_slots(const VhostShadowVirtqueue *svq)
70 {
71     return svq->vring.num - (svq->shadow_avail_idx - svq->shadow_used_idx);
72 }
73 
74 /**
75  * Translate addresses between the qemu's virtual address and the SVQ IOVA
76  *
77  * @svq: Shadow VirtQueue
78  * @vaddr: Translated IOVA addresses
79  * @iovec: Source qemu's VA addresses
80  * @num: Length of iovec and minimum length of vaddr
81  */
82 static bool vhost_svq_translate_addr(const VhostShadowVirtqueue *svq,
83                                      hwaddr *addrs, const struct iovec *iovec,
84                                      size_t num)
85 {
86     if (num == 0) {
87         return true;
88     }
89 
90     for (size_t i = 0; i < num; ++i) {
91         DMAMap needle = {
92             .translated_addr = (hwaddr)(uintptr_t)iovec[i].iov_base,
93             .size = iovec[i].iov_len,
94         };
95         Int128 needle_last, map_last;
96         size_t off;
97 
98         const DMAMap *map = vhost_iova_tree_find_iova(svq->iova_tree, &needle);
99         /*
100          * Map cannot be NULL since iova map contains all guest space and
101          * qemu already has a physical address mapped
102          */
103         if (unlikely(!map)) {
104             qemu_log_mask(LOG_GUEST_ERROR,
105                           "Invalid address 0x%"HWADDR_PRIx" given by guest",
106                           needle.translated_addr);
107             return false;
108         }
109 
110         off = needle.translated_addr - map->translated_addr;
111         addrs[i] = map->iova + off;
112 
113         needle_last = int128_add(int128_make64(needle.translated_addr),
114                                  int128_make64(iovec[i].iov_len));
115         map_last = int128_make64(map->translated_addr + map->size);
116         if (unlikely(int128_gt(needle_last, map_last))) {
117             qemu_log_mask(LOG_GUEST_ERROR,
118                           "Guest buffer expands over iova range");
119             return false;
120         }
121     }
122 
123     return true;
124 }
125 
126 /**
127  * Write descriptors to SVQ vring
128  *
129  * @svq: The shadow virtqueue
130  * @sg: Cache for hwaddr
131  * @iovec: The iovec from the guest
132  * @num: iovec length
133  * @more_descs: True if more descriptors come in the chain
134  * @write: True if they are writeable descriptors
135  *
136  * Return true if success, false otherwise and print error.
137  */
138 static bool vhost_svq_vring_write_descs(VhostShadowVirtqueue *svq, hwaddr *sg,
139                                         const struct iovec *iovec, size_t num,
140                                         bool more_descs, bool write)
141 {
142     uint16_t i = svq->free_head, last = svq->free_head;
143     unsigned n;
144     uint16_t flags = write ? cpu_to_le16(VRING_DESC_F_WRITE) : 0;
145     vring_desc_t *descs = svq->vring.desc;
146     bool ok;
147 
148     if (num == 0) {
149         return true;
150     }
151 
152     ok = vhost_svq_translate_addr(svq, sg, iovec, num);
153     if (unlikely(!ok)) {
154         return false;
155     }
156 
157     for (n = 0; n < num; n++) {
158         if (more_descs || (n + 1 < num)) {
159             descs[i].flags = flags | cpu_to_le16(VRING_DESC_F_NEXT);
160             descs[i].next = cpu_to_le16(svq->desc_next[i]);
161         } else {
162             descs[i].flags = flags;
163         }
164         descs[i].addr = cpu_to_le64(sg[n]);
165         descs[i].len = cpu_to_le32(iovec[n].iov_len);
166 
167         last = i;
168         i = cpu_to_le16(svq->desc_next[i]);
169     }
170 
171     svq->free_head = le16_to_cpu(svq->desc_next[last]);
172     return true;
173 }
174 
175 static bool vhost_svq_add_split(VhostShadowVirtqueue *svq,
176                                 const struct iovec *out_sg, size_t out_num,
177                                 const struct iovec *in_sg, size_t in_num,
178                                 unsigned *head)
179 {
180     unsigned avail_idx;
181     vring_avail_t *avail = svq->vring.avail;
182     bool ok;
183     g_autofree hwaddr *sgs = g_new(hwaddr, MAX(out_num, in_num));
184 
185     *head = svq->free_head;
186 
187     /* We need some descriptors here */
188     if (unlikely(!out_num && !in_num)) {
189         qemu_log_mask(LOG_GUEST_ERROR,
190                       "Guest provided element with no descriptors");
191         return false;
192     }
193 
194     ok = vhost_svq_vring_write_descs(svq, sgs, out_sg, out_num, in_num > 0,
195                                      false);
196     if (unlikely(!ok)) {
197         return false;
198     }
199 
200     ok = vhost_svq_vring_write_descs(svq, sgs, in_sg, in_num, false, true);
201     if (unlikely(!ok)) {
202         return false;
203     }
204 
205     /*
206      * Put the entry in the available array (but don't update avail->idx until
207      * they do sync).
208      */
209     avail_idx = svq->shadow_avail_idx & (svq->vring.num - 1);
210     avail->ring[avail_idx] = cpu_to_le16(*head);
211     svq->shadow_avail_idx++;
212 
213     /* Update the avail index after write the descriptor */
214     smp_wmb();
215     avail->idx = cpu_to_le16(svq->shadow_avail_idx);
216 
217     return true;
218 }
219 
220 static void vhost_svq_kick(VhostShadowVirtqueue *svq)
221 {
222     bool needs_kick;
223 
224     /*
225      * We need to expose the available array entries before checking the used
226      * flags
227      */
228     smp_mb();
229 
230     if (virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
231         uint16_t avail_event = *(uint16_t *)(&svq->vring.used->ring[svq->vring.num]);
232         needs_kick = vring_need_event(avail_event, svq->shadow_avail_idx, svq->shadow_avail_idx - 1);
233     } else {
234         needs_kick = !(svq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
235     }
236 
237     if (!needs_kick) {
238         return;
239     }
240 
241     event_notifier_set(&svq->hdev_kick);
242 }
243 
244 /**
245  * Add an element to a SVQ.
246  *
247  * Return -EINVAL if element is invalid, -ENOSPC if dev queue is full
248  */
249 int vhost_svq_add(VhostShadowVirtqueue *svq, const struct iovec *out_sg,
250                   size_t out_num, const struct iovec *in_sg, size_t in_num,
251                   VirtQueueElement *elem)
252 {
253     unsigned qemu_head;
254     unsigned ndescs = in_num + out_num;
255     bool ok;
256 
257     if (unlikely(ndescs > vhost_svq_available_slots(svq))) {
258         return -ENOSPC;
259     }
260 
261     ok = vhost_svq_add_split(svq, out_sg, out_num, in_sg, in_num, &qemu_head);
262     if (unlikely(!ok)) {
263         return -EINVAL;
264     }
265 
266     svq->desc_state[qemu_head].elem = elem;
267     svq->desc_state[qemu_head].ndescs = ndescs;
268     vhost_svq_kick(svq);
269     return 0;
270 }
271 
272 /* Convenience wrapper to add a guest's element to SVQ */
273 static int vhost_svq_add_element(VhostShadowVirtqueue *svq,
274                                  VirtQueueElement *elem)
275 {
276     return vhost_svq_add(svq, elem->out_sg, elem->out_num, elem->in_sg,
277                          elem->in_num, elem);
278 }
279 
280 /**
281  * Forward available buffers.
282  *
283  * @svq: Shadow VirtQueue
284  *
285  * Note that this function does not guarantee that all guest's available
286  * buffers are available to the device in SVQ avail ring. The guest may have
287  * exposed a GPA / GIOVA contiguous buffer, but it may not be contiguous in
288  * qemu vaddr.
289  *
290  * If that happens, guest's kick notifications will be disabled until the
291  * device uses some buffers.
292  */
293 static void vhost_handle_guest_kick(VhostShadowVirtqueue *svq)
294 {
295     /* Clear event notifier */
296     event_notifier_test_and_clear(&svq->svq_kick);
297 
298     /* Forward to the device as many available buffers as possible */
299     do {
300         virtio_queue_set_notification(svq->vq, false);
301 
302         while (true) {
303             g_autofree VirtQueueElement *elem = NULL;
304             int r;
305 
306             if (svq->next_guest_avail_elem) {
307                 elem = g_steal_pointer(&svq->next_guest_avail_elem);
308             } else {
309                 elem = virtqueue_pop(svq->vq, sizeof(*elem));
310             }
311 
312             if (!elem) {
313                 break;
314             }
315 
316             if (svq->ops) {
317                 r = svq->ops->avail_handler(svq, elem, svq->ops_opaque);
318             } else {
319                 r = vhost_svq_add_element(svq, elem);
320             }
321             if (unlikely(r != 0)) {
322                 if (r == -ENOSPC) {
323                     /*
324                      * This condition is possible since a contiguous buffer in
325                      * GPA does not imply a contiguous buffer in qemu's VA
326                      * scatter-gather segments. If that happens, the buffer
327                      * exposed to the device needs to be a chain of descriptors
328                      * at this moment.
329                      *
330                      * SVQ cannot hold more available buffers if we are here:
331                      * queue the current guest descriptor and ignore kicks
332                      * until some elements are used.
333                      */
334                     svq->next_guest_avail_elem = g_steal_pointer(&elem);
335                 }
336 
337                 /* VQ is full or broken, just return and ignore kicks */
338                 return;
339             }
340             /* elem belongs to SVQ or external caller now */
341             elem = NULL;
342         }
343 
344         virtio_queue_set_notification(svq->vq, true);
345     } while (!virtio_queue_empty(svq->vq));
346 }
347 
348 /**
349  * Handle guest's kick.
350  *
351  * @n: guest kick event notifier, the one that guest set to notify svq.
352  */
353 static void vhost_handle_guest_kick_notifier(EventNotifier *n)
354 {
355     VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue, svq_kick);
356     event_notifier_test_and_clear(n);
357     vhost_handle_guest_kick(svq);
358 }
359 
360 static bool vhost_svq_more_used(VhostShadowVirtqueue *svq)
361 {
362     uint16_t *used_idx = &svq->vring.used->idx;
363     if (svq->last_used_idx != svq->shadow_used_idx) {
364         return true;
365     }
366 
367     svq->shadow_used_idx = cpu_to_le16(*(volatile uint16_t *)used_idx);
368 
369     return svq->last_used_idx != svq->shadow_used_idx;
370 }
371 
372 /**
373  * Enable vhost device calls after disable them.
374  *
375  * @svq: The svq
376  *
377  * It returns false if there are pending used buffers from the vhost device,
378  * avoiding the possible races between SVQ checking for more work and enabling
379  * callbacks. True if SVQ used vring has no more pending buffers.
380  */
381 static bool vhost_svq_enable_notification(VhostShadowVirtqueue *svq)
382 {
383     if (virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
384         uint16_t *used_event = (uint16_t *)&svq->vring.avail->ring[svq->vring.num];
385         *used_event = svq->shadow_used_idx;
386     } else {
387         svq->vring.avail->flags &= ~cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
388     }
389 
390     /* Make sure the event is enabled before the read of used_idx */
391     smp_mb();
392     return !vhost_svq_more_used(svq);
393 }
394 
395 static void vhost_svq_disable_notification(VhostShadowVirtqueue *svq)
396 {
397     /*
398      * No need to disable notification in the event idx case, since used event
399      * index is already an index too far away.
400      */
401     if (!virtio_vdev_has_feature(svq->vdev, VIRTIO_RING_F_EVENT_IDX)) {
402         svq->vring.avail->flags |= cpu_to_le16(VRING_AVAIL_F_NO_INTERRUPT);
403     }
404 }
405 
406 static uint16_t vhost_svq_last_desc_of_chain(const VhostShadowVirtqueue *svq,
407                                              uint16_t num, uint16_t i)
408 {
409     for (uint16_t j = 0; j < (num - 1); ++j) {
410         i = le16_to_cpu(svq->desc_next[i]);
411     }
412 
413     return i;
414 }
415 
416 static VirtQueueElement *vhost_svq_get_buf(VhostShadowVirtqueue *svq,
417                                            uint32_t *len)
418 {
419     const vring_used_t *used = svq->vring.used;
420     vring_used_elem_t used_elem;
421     uint16_t last_used, last_used_chain, num;
422 
423     if (!vhost_svq_more_used(svq)) {
424         return NULL;
425     }
426 
427     /* Only get used array entries after they have been exposed by dev */
428     smp_rmb();
429     last_used = svq->last_used_idx & (svq->vring.num - 1);
430     used_elem.id = le32_to_cpu(used->ring[last_used].id);
431     used_elem.len = le32_to_cpu(used->ring[last_used].len);
432 
433     svq->last_used_idx++;
434     if (unlikely(used_elem.id >= svq->vring.num)) {
435         qemu_log_mask(LOG_GUEST_ERROR, "Device %s says index %u is used",
436                       svq->vdev->name, used_elem.id);
437         return NULL;
438     }
439 
440     if (unlikely(!svq->desc_state[used_elem.id].ndescs)) {
441         qemu_log_mask(LOG_GUEST_ERROR,
442             "Device %s says index %u is used, but it was not available",
443             svq->vdev->name, used_elem.id);
444         return NULL;
445     }
446 
447     num = svq->desc_state[used_elem.id].ndescs;
448     svq->desc_state[used_elem.id].ndescs = 0;
449     last_used_chain = vhost_svq_last_desc_of_chain(svq, num, used_elem.id);
450     svq->desc_next[last_used_chain] = svq->free_head;
451     svq->free_head = used_elem.id;
452 
453     *len = used_elem.len;
454     return g_steal_pointer(&svq->desc_state[used_elem.id].elem);
455 }
456 
457 /**
458  * Push an element to SVQ, returning it to the guest.
459  */
460 void vhost_svq_push_elem(VhostShadowVirtqueue *svq,
461                          const VirtQueueElement *elem, uint32_t len)
462 {
463     virtqueue_push(svq->vq, elem, len);
464     if (svq->next_guest_avail_elem) {
465         /*
466          * Avail ring was full when vhost_svq_flush was called, so it's a
467          * good moment to make more descriptors available if possible.
468          */
469         vhost_handle_guest_kick(svq);
470     }
471 }
472 
473 static void vhost_svq_flush(VhostShadowVirtqueue *svq,
474                             bool check_for_avail_queue)
475 {
476     VirtQueue *vq = svq->vq;
477 
478     /* Forward as many used buffers as possible. */
479     do {
480         unsigned i = 0;
481 
482         vhost_svq_disable_notification(svq);
483         while (true) {
484             uint32_t len;
485             g_autofree VirtQueueElement *elem = vhost_svq_get_buf(svq, &len);
486             if (!elem) {
487                 break;
488             }
489 
490             if (unlikely(i >= svq->vring.num)) {
491                 qemu_log_mask(LOG_GUEST_ERROR,
492                          "More than %u used buffers obtained in a %u size SVQ",
493                          i, svq->vring.num);
494                 virtqueue_fill(vq, elem, len, i);
495                 virtqueue_flush(vq, i);
496                 return;
497             }
498             virtqueue_fill(vq, elem, len, i++);
499         }
500 
501         virtqueue_flush(vq, i);
502         event_notifier_set(&svq->svq_call);
503 
504         if (check_for_avail_queue && svq->next_guest_avail_elem) {
505             /*
506              * Avail ring was full when vhost_svq_flush was called, so it's a
507              * good moment to make more descriptors available if possible.
508              */
509             vhost_handle_guest_kick(svq);
510         }
511     } while (!vhost_svq_enable_notification(svq));
512 }
513 
514 /**
515  * Poll the SVQ for one device used buffer.
516  *
517  * This function race with main event loop SVQ polling, so extra
518  * synchronization is needed.
519  *
520  * Return the length written by the device.
521  */
522 size_t vhost_svq_poll(VhostShadowVirtqueue *svq)
523 {
524     int64_t start_us = g_get_monotonic_time();
525     uint32_t len = 0;
526 
527     do {
528         if (vhost_svq_more_used(svq)) {
529             break;
530         }
531 
532         if (unlikely(g_get_monotonic_time() - start_us > 10e6)) {
533             return 0;
534         }
535     } while (true);
536 
537     vhost_svq_get_buf(svq, &len);
538     return len;
539 }
540 
541 /**
542  * Forward used buffers.
543  *
544  * @n: hdev call event notifier, the one that device set to notify svq.
545  *
546  * Note that we are not making any buffers available in the loop, there is no
547  * way that it runs more than virtqueue size times.
548  */
549 static void vhost_svq_handle_call(EventNotifier *n)
550 {
551     VhostShadowVirtqueue *svq = container_of(n, VhostShadowVirtqueue,
552                                              hdev_call);
553     event_notifier_test_and_clear(n);
554     vhost_svq_flush(svq, true);
555 }
556 
557 /**
558  * Set the call notifier for the SVQ to call the guest
559  *
560  * @svq: Shadow virtqueue
561  * @call_fd: call notifier
562  *
563  * Called on BQL context.
564  */
565 void vhost_svq_set_svq_call_fd(VhostShadowVirtqueue *svq, int call_fd)
566 {
567     if (call_fd == VHOST_FILE_UNBIND) {
568         /*
569          * Fail event_notifier_set if called handling device call.
570          *
571          * SVQ still needs device notifications, since it needs to keep
572          * forwarding used buffers even with the unbind.
573          */
574         memset(&svq->svq_call, 0, sizeof(svq->svq_call));
575     } else {
576         event_notifier_init_fd(&svq->svq_call, call_fd);
577     }
578 }
579 
580 /**
581  * Get the shadow vq vring address.
582  * @svq: Shadow virtqueue
583  * @addr: Destination to store address
584  */
585 void vhost_svq_get_vring_addr(const VhostShadowVirtqueue *svq,
586                               struct vhost_vring_addr *addr)
587 {
588     addr->desc_user_addr = (uint64_t)(uintptr_t)svq->vring.desc;
589     addr->avail_user_addr = (uint64_t)(uintptr_t)svq->vring.avail;
590     addr->used_user_addr = (uint64_t)(uintptr_t)svq->vring.used;
591 }
592 
593 size_t vhost_svq_driver_area_size(const VhostShadowVirtqueue *svq)
594 {
595     size_t desc_size = sizeof(vring_desc_t) * svq->vring.num;
596     size_t avail_size = offsetof(vring_avail_t, ring[svq->vring.num]) +
597                                                               sizeof(uint16_t);
598 
599     return ROUND_UP(desc_size + avail_size, qemu_real_host_page_size());
600 }
601 
602 size_t vhost_svq_device_area_size(const VhostShadowVirtqueue *svq)
603 {
604     size_t used_size = offsetof(vring_used_t, ring[svq->vring.num]) +
605                                                               sizeof(uint16_t);
606     return ROUND_UP(used_size, qemu_real_host_page_size());
607 }
608 
609 /**
610  * Set a new file descriptor for the guest to kick the SVQ and notify for avail
611  *
612  * @svq: The svq
613  * @svq_kick_fd: The svq kick fd
614  *
615  * Note that the SVQ will never close the old file descriptor.
616  */
617 void vhost_svq_set_svq_kick_fd(VhostShadowVirtqueue *svq, int svq_kick_fd)
618 {
619     EventNotifier *svq_kick = &svq->svq_kick;
620     bool poll_stop = VHOST_FILE_UNBIND != event_notifier_get_fd(svq_kick);
621     bool poll_start = svq_kick_fd != VHOST_FILE_UNBIND;
622 
623     if (poll_stop) {
624         event_notifier_set_handler(svq_kick, NULL);
625     }
626 
627     event_notifier_init_fd(svq_kick, svq_kick_fd);
628     /*
629      * event_notifier_set_handler already checks for guest's notifications if
630      * they arrive at the new file descriptor in the switch, so there is no
631      * need to explicitly check for them.
632      */
633     if (poll_start) {
634         event_notifier_set(svq_kick);
635         event_notifier_set_handler(svq_kick, vhost_handle_guest_kick_notifier);
636     }
637 }
638 
639 /**
640  * Start the shadow virtqueue operation.
641  *
642  * @svq: Shadow Virtqueue
643  * @vdev: VirtIO device
644  * @vq: Virtqueue to shadow
645  * @iova_tree: Tree to perform descriptors translations
646  */
647 void vhost_svq_start(VhostShadowVirtqueue *svq, VirtIODevice *vdev,
648                      VirtQueue *vq, VhostIOVATree *iova_tree)
649 {
650     size_t desc_size, driver_size, device_size;
651 
652     event_notifier_set_handler(&svq->hdev_call, vhost_svq_handle_call);
653     svq->next_guest_avail_elem = NULL;
654     svq->shadow_avail_idx = 0;
655     svq->shadow_used_idx = 0;
656     svq->last_used_idx = 0;
657     svq->vdev = vdev;
658     svq->vq = vq;
659     svq->iova_tree = iova_tree;
660 
661     svq->vring.num = virtio_queue_get_num(vdev, virtio_get_queue_index(vq));
662     driver_size = vhost_svq_driver_area_size(svq);
663     device_size = vhost_svq_device_area_size(svq);
664     svq->vring.desc = qemu_memalign(qemu_real_host_page_size(), driver_size);
665     desc_size = sizeof(vring_desc_t) * svq->vring.num;
666     svq->vring.avail = (void *)((char *)svq->vring.desc + desc_size);
667     memset(svq->vring.desc, 0, driver_size);
668     svq->vring.used = qemu_memalign(qemu_real_host_page_size(), device_size);
669     memset(svq->vring.used, 0, device_size);
670     svq->desc_state = g_new0(SVQDescState, svq->vring.num);
671     svq->desc_next = g_new0(uint16_t, svq->vring.num);
672     for (unsigned i = 0; i < svq->vring.num - 1; i++) {
673         svq->desc_next[i] = cpu_to_le16(i + 1);
674     }
675 }
676 
677 /**
678  * Stop the shadow virtqueue operation.
679  * @svq: Shadow Virtqueue
680  */
681 void vhost_svq_stop(VhostShadowVirtqueue *svq)
682 {
683     vhost_svq_set_svq_kick_fd(svq, VHOST_FILE_UNBIND);
684     g_autofree VirtQueueElement *next_avail_elem = NULL;
685 
686     if (!svq->vq) {
687         return;
688     }
689 
690     /* Send all pending used descriptors to guest */
691     vhost_svq_flush(svq, false);
692 
693     for (unsigned i = 0; i < svq->vring.num; ++i) {
694         g_autofree VirtQueueElement *elem = NULL;
695         elem = g_steal_pointer(&svq->desc_state[i].elem);
696         if (elem) {
697             virtqueue_detach_element(svq->vq, elem, 0);
698         }
699     }
700 
701     next_avail_elem = g_steal_pointer(&svq->next_guest_avail_elem);
702     if (next_avail_elem) {
703         virtqueue_detach_element(svq->vq, next_avail_elem, 0);
704     }
705     svq->vq = NULL;
706     g_free(svq->desc_next);
707     g_free(svq->desc_state);
708     qemu_vfree(svq->vring.desc);
709     qemu_vfree(svq->vring.used);
710     event_notifier_set_handler(&svq->hdev_call, NULL);
711 }
712 
713 /**
714  * Creates vhost shadow virtqueue, and instructs the vhost device to use the
715  * shadow methods and file descriptors.
716  *
717  * @ops: SVQ owner callbacks
718  * @ops_opaque: ops opaque pointer
719  */
720 VhostShadowVirtqueue *vhost_svq_new(const VhostShadowVirtqueueOps *ops,
721                                     void *ops_opaque)
722 {
723     VhostShadowVirtqueue *svq = g_new0(VhostShadowVirtqueue, 1);
724 
725     event_notifier_init_fd(&svq->svq_kick, VHOST_FILE_UNBIND);
726     svq->ops = ops;
727     svq->ops_opaque = ops_opaque;
728     return svq;
729 }
730 
731 /**
732  * Free the resources of the shadow virtqueue.
733  *
734  * @pvq: gpointer to SVQ so it can be used by autofree functions.
735  */
736 void vhost_svq_free(gpointer pvq)
737 {
738     VhostShadowVirtqueue *vq = pvq;
739     vhost_svq_stop(vq);
740     g_free(vq);
741 }
742