1 /* Virtio ring implementation.
3 * Copyright 2007 Rusty Russell IBM Corporation
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, write to the Free Software
17 * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
19 #include <linux/virtio.h>
20 #include <linux/virtio_ring.h>
21 #include <linux/virtio_config.h>
22 #include <linux/device.h>
23 #include <linux/slab.h>
24 #include <linux/module.h>
25 #include <linux/hrtimer.h>
27 /* virtio guest is communicating with a virtual "device" that actually runs on
28 * a host processor. Memory barriers are used to control SMP effects. */
30 /* Where possible, use SMP barriers which are more lightweight than mandatory
31 * barriers, because mandatory barriers control MMIO effects on accesses
32 * through relaxed memory I/O windows (which virtio-pci does not use). */
33 #define virtio_mb(vq) \
34 do { if ((vq)->weak_barriers) smp_mb(); else mb(); } while(0)
35 #define virtio_rmb(vq) \
36 do { if ((vq)->weak_barriers) smp_rmb(); else rmb(); } while(0)
37 #define virtio_wmb(vq) \
38 do { if ((vq)->weak_barriers) smp_wmb(); else wmb(); } while(0)
40 /* We must force memory ordering even if guest is UP since host could be
41 * running on another CPU, but SMP barriers are defined to barrier() in that
42 * configuration. So fall back to mandatory barriers instead. */
43 #define virtio_mb(vq) mb()
44 #define virtio_rmb(vq) rmb()
45 #define virtio_wmb(vq) wmb()
49 /* For development, we want to crash whenever the ring is screwed. */
50 #define BAD_RING(_vq, fmt, args...) \
52 dev_err(&(_vq)->vq.vdev->dev, \
53 "%s:"fmt, (_vq)->vq.name, ##args); \
56 /* Caller is supposed to guarantee no reentry. */
57 #define START_USE(_vq) \
60 panic("%s:in_use = %i\n", \
61 (_vq)->vq.name, (_vq)->in_use); \
62 (_vq)->in_use = __LINE__; \
64 #define END_USE(_vq) \
65 do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
67 #define BAD_RING(_vq, fmt, args...) \
69 dev_err(&_vq->vq.vdev->dev, \
70 "%s:"fmt, (_vq)->vq.name, ##args); \
71 (_vq)->broken = true; \
77 struct vring_virtqueue
81 /* Actual memory layout for this queue */
84 /* Can we use weak barriers? */
87 /* Other side has made a mess, don't try any more. */
90 /* Host supports indirect buffers */
93 /* Host publishes avail event idx */
96 /* Number of free buffers */
97 unsigned int num_free;
98 /* Head of free buffer list. */
99 unsigned int free_head;
100 /* Number we've added since last sync. */
101 unsigned int num_added;
103 /* Last used index we've seen. */
106 /* How to notify other side. FIXME: commonalize hcalls! */
107 void (*notify)(struct virtqueue *vq);
109 /* Index of the queue */
113 /* They're supposed to lock for us. */
116 /* Figure out if their kicks are too delayed. */
117 bool last_add_time_valid;
118 ktime_t last_add_time;
121 /* Tokens for callbacks. */
125 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
127 /* Set up an indirect table of descriptors and add it to the queue. */
128 static int vring_add_indirect(struct vring_virtqueue *vq,
129 struct scatterlist sg[],
134 struct vring_desc *desc;
138 desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
142 /* Transfer entries from the sg list into the indirect page */
143 for (i = 0; i < out; i++) {
144 desc[i].flags = VRING_DESC_F_NEXT;
145 desc[i].addr = sg_phys(sg);
146 desc[i].len = sg->length;
150 for (; i < (out + in); i++) {
151 desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
152 desc[i].addr = sg_phys(sg);
153 desc[i].len = sg->length;
158 /* Last one doesn't continue. */
159 desc[i-1].flags &= ~VRING_DESC_F_NEXT;
162 /* We're about to use a buffer */
165 /* Use a single buffer which doesn't continue */
166 head = vq->free_head;
167 vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
168 vq->vring.desc[head].addr = virt_to_phys(desc);
169 vq->vring.desc[head].len = i * sizeof(struct vring_desc);
171 /* Update free pointer */
172 vq->free_head = vq->vring.desc[head].next;
177 int virtqueue_get_queue_index(struct virtqueue *_vq)
179 struct vring_virtqueue *vq = to_vvq(_vq);
180 return vq->queue_index;
182 EXPORT_SYMBOL_GPL(virtqueue_get_queue_index);
185 * virtqueue_add_buf - expose buffer to other end
186 * @vq: the struct virtqueue we're talking about.
187 * @sg: the description of the buffer(s).
188 * @out_num: the number of sg readable by other side
189 * @in_num: the number of sg which are writable (after readable ones)
190 * @data: the token identifying the buffer.
191 * @gfp: how to do memory allocations (if necessary).
193 * Caller must ensure we don't call this with other virtqueue operations
194 * at the same time (except where noted).
196 * Returns remaining capacity of queue or a negative error
197 * (ie. ENOSPC). Note that it only really makes sense to treat all
198 * positive return values as "available": indirect buffers mean that
199 * we can put an entire sg[] array inside a single queue entry.
201 int virtqueue_add_buf(struct virtqueue *_vq,
202 struct scatterlist sg[],
208 struct vring_virtqueue *vq = to_vvq(_vq);
209 unsigned int i, avail, uninitialized_var(prev);
214 BUG_ON(data == NULL);
218 ktime_t now = ktime_get();
220 /* No kick or get, with .1 second between? Warn. */
221 if (vq->last_add_time_valid)
222 WARN_ON(ktime_to_ms(ktime_sub(now, vq->last_add_time))
224 vq->last_add_time = now;
225 vq->last_add_time_valid = true;
229 /* If the host supports indirect descriptor tables, and we have multiple
230 * buffers, then go indirect. FIXME: tune this threshold */
231 if (vq->indirect && (out + in) > 1 && vq->num_free) {
232 head = vring_add_indirect(vq, sg, out, in, gfp);
233 if (likely(head >= 0))
237 BUG_ON(out + in > vq->vring.num);
238 BUG_ON(out + in == 0);
240 if (vq->num_free < out + in) {
241 pr_debug("Can't add buf len %i - avail = %i\n",
242 out + in, vq->num_free);
243 /* FIXME: for historical reasons, we force a notify here if
244 * there are outgoing parts to the buffer. Presumably the
245 * host should service the ring ASAP. */
252 /* We're about to use some buffers from the free list. */
253 vq->num_free -= out + in;
255 head = vq->free_head;
256 for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
257 vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
258 vq->vring.desc[i].addr = sg_phys(sg);
259 vq->vring.desc[i].len = sg->length;
263 for (; in; i = vq->vring.desc[i].next, in--) {
264 vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
265 vq->vring.desc[i].addr = sg_phys(sg);
266 vq->vring.desc[i].len = sg->length;
270 /* Last one doesn't continue. */
271 vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
273 /* Update free pointer */
278 vq->data[head] = data;
280 /* Put entry in available array (but don't update avail->idx until they
282 avail = (vq->vring.avail->idx & (vq->vring.num-1));
283 vq->vring.avail->ring[avail] = head;
285 /* Descriptors and available array need to be set before we expose the
286 * new available array entries. */
288 vq->vring.avail->idx++;
291 /* This is very unlikely, but theoretically possible. Kick
293 if (unlikely(vq->num_added == (1 << 16) - 1))
296 pr_debug("Added buffer head %i to %p\n", head, vq);
301 EXPORT_SYMBOL_GPL(virtqueue_add_buf);
304 * virtqueue_kick_prepare - first half of split virtqueue_kick call.
305 * @vq: the struct virtqueue
307 * Instead of virtqueue_kick(), you can do:
308 * if (virtqueue_kick_prepare(vq))
309 * virtqueue_notify(vq);
311 * This is sometimes useful because the virtqueue_kick_prepare() needs
312 * to be serialized, but the actual virtqueue_notify() call does not.
314 bool virtqueue_kick_prepare(struct virtqueue *_vq)
316 struct vring_virtqueue *vq = to_vvq(_vq);
321 /* We need to expose available array entries before checking avail
325 old = vq->vring.avail->idx - vq->num_added;
326 new = vq->vring.avail->idx;
330 if (vq->last_add_time_valid) {
331 WARN_ON(ktime_to_ms(ktime_sub(ktime_get(),
332 vq->last_add_time)) > 100);
334 vq->last_add_time_valid = false;
338 needs_kick = vring_need_event(vring_avail_event(&vq->vring),
341 needs_kick = !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY);
346 EXPORT_SYMBOL_GPL(virtqueue_kick_prepare);
349 * virtqueue_notify - second half of split virtqueue_kick call.
350 * @vq: the struct virtqueue
352 * This does not need to be serialized.
354 void virtqueue_notify(struct virtqueue *_vq)
356 struct vring_virtqueue *vq = to_vvq(_vq);
358 /* Prod other side to tell it about changes. */
361 EXPORT_SYMBOL_GPL(virtqueue_notify);
364 * virtqueue_kick - update after add_buf
365 * @vq: the struct virtqueue
367 * After one or more virtqueue_add_buf calls, invoke this to kick
370 * Caller must ensure we don't call this with other virtqueue
371 * operations at the same time (except where noted).
373 void virtqueue_kick(struct virtqueue *vq)
375 if (virtqueue_kick_prepare(vq))
376 virtqueue_notify(vq);
378 EXPORT_SYMBOL_GPL(virtqueue_kick);
380 static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
384 /* Clear data ptr. */
385 vq->data[head] = NULL;
387 /* Put back on free list: find end */
390 /* Free the indirect table */
391 if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
392 kfree(phys_to_virt(vq->vring.desc[i].addr));
394 while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
395 i = vq->vring.desc[i].next;
399 vq->vring.desc[i].next = vq->free_head;
400 vq->free_head = head;
401 /* Plus final descriptor */
405 static inline bool more_used(const struct vring_virtqueue *vq)
407 return vq->last_used_idx != vq->vring.used->idx;
411 * virtqueue_get_buf - get the next used buffer
412 * @vq: the struct virtqueue we're talking about.
413 * @len: the length written into the buffer
415 * If the driver wrote data into the buffer, @len will be set to the
416 * amount written. This means you don't need to clear the buffer
417 * beforehand to ensure there's no data leakage in the case of short
420 * Caller must ensure we don't call this with other virtqueue
421 * operations at the same time (except where noted).
423 * Returns NULL if there are no used buffers, or the "data" token
424 * handed to virtqueue_add_buf().
426 void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
428 struct vring_virtqueue *vq = to_vvq(_vq);
435 if (unlikely(vq->broken)) {
440 if (!more_used(vq)) {
441 pr_debug("No more buffers in queue\n");
446 /* Only get used array entries after they have been exposed by host. */
449 last_used = (vq->last_used_idx & (vq->vring.num - 1));
450 i = vq->vring.used->ring[last_used].id;
451 *len = vq->vring.used->ring[last_used].len;
453 if (unlikely(i >= vq->vring.num)) {
454 BAD_RING(vq, "id %u out of range\n", i);
457 if (unlikely(!vq->data[i])) {
458 BAD_RING(vq, "id %u is not a head!\n", i);
462 /* detach_buf clears data, so grab it now. */
466 /* If we expect an interrupt for the next entry, tell host
467 * by writing event index and flush out the write before
468 * the read in the next get_buf call. */
469 if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) {
470 vring_used_event(&vq->vring) = vq->last_used_idx;
475 vq->last_add_time_valid = false;
481 EXPORT_SYMBOL_GPL(virtqueue_get_buf);
484 * virtqueue_disable_cb - disable callbacks
485 * @vq: the struct virtqueue we're talking about.
487 * Note that this is not necessarily synchronous, hence unreliable and only
488 * useful as an optimization.
490 * Unlike other operations, this need not be serialized.
492 void virtqueue_disable_cb(struct virtqueue *_vq)
494 struct vring_virtqueue *vq = to_vvq(_vq);
496 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
498 EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
501 * virtqueue_enable_cb - restart callbacks after disable_cb.
502 * @vq: the struct virtqueue we're talking about.
504 * This re-enables callbacks; it returns "false" if there are pending
505 * buffers in the queue, to detect a possible race between the driver
506 * checking for more work, and enabling callbacks.
508 * Caller must ensure we don't call this with other virtqueue
509 * operations at the same time (except where noted).
511 bool virtqueue_enable_cb(struct virtqueue *_vq)
513 struct vring_virtqueue *vq = to_vvq(_vq);
517 /* We optimistically turn back on interrupts, then check if there was
519 /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
520 * either clear the flags bit or point the event index at the next
521 * entry. Always do both to keep code simple. */
522 vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
523 vring_used_event(&vq->vring) = vq->last_used_idx;
525 if (unlikely(more_used(vq))) {
533 EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
536 * virtqueue_enable_cb_delayed - restart callbacks after disable_cb.
537 * @vq: the struct virtqueue we're talking about.
539 * This re-enables callbacks but hints to the other side to delay
540 * interrupts until most of the available buffers have been processed;
541 * it returns "false" if there are many pending buffers in the queue,
542 * to detect a possible race between the driver checking for more work,
543 * and enabling callbacks.
545 * Caller must ensure we don't call this with other virtqueue
546 * operations at the same time (except where noted).
548 bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
550 struct vring_virtqueue *vq = to_vvq(_vq);
555 /* We optimistically turn back on interrupts, then check if there was
557 /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
558 * either clear the flags bit or point the event index at the next
559 * entry. Always do both to keep code simple. */
560 vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
561 /* TODO: tune this threshold */
562 bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
563 vring_used_event(&vq->vring) = vq->last_used_idx + bufs;
565 if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) {
573 EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
576 * virtqueue_detach_unused_buf - detach first unused buffer
577 * @vq: the struct virtqueue we're talking about.
579 * Returns NULL or the "data" token handed to virtqueue_add_buf().
580 * This is not valid on an active queue; it is useful only for device
583 void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
585 struct vring_virtqueue *vq = to_vvq(_vq);
591 for (i = 0; i < vq->vring.num; i++) {
594 /* detach_buf clears data, so grab it now. */
597 vq->vring.avail->idx--;
601 /* That should have freed everything. */
602 BUG_ON(vq->num_free != vq->vring.num);
607 EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
609 irqreturn_t vring_interrupt(int irq, void *_vq)
611 struct vring_virtqueue *vq = to_vvq(_vq);
613 if (!more_used(vq)) {
614 pr_debug("virtqueue interrupt with no work for %p\n", vq);
618 if (unlikely(vq->broken))
621 pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
623 vq->vq.callback(&vq->vq);
627 EXPORT_SYMBOL_GPL(vring_interrupt);
629 struct virtqueue *vring_new_virtqueue(unsigned int index,
631 unsigned int vring_align,
632 struct virtio_device *vdev,
635 void (*notify)(struct virtqueue *),
636 void (*callback)(struct virtqueue *),
639 struct vring_virtqueue *vq;
642 /* We assume num is a power of 2. */
643 if (num & (num - 1)) {
644 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
648 vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
652 vring_init(&vq->vring, num, pages, vring_align);
653 vq->vq.callback = callback;
657 vq->weak_barriers = weak_barriers;
659 vq->last_used_idx = 0;
661 vq->queue_index = index;
662 list_add_tail(&vq->vq.list, &vdev->vqs);
665 vq->last_add_time_valid = false;
668 vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
669 vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
671 /* No callback? Tell other side not to bother us. */
673 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
675 /* Put everything in free lists. */
678 for (i = 0; i < num-1; i++) {
679 vq->vring.desc[i].next = i+1;
686 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
688 void vring_del_virtqueue(struct virtqueue *vq)
693 EXPORT_SYMBOL_GPL(vring_del_virtqueue);
695 /* Manipulates transport-specific feature bits. */
696 void vring_transport_features(struct virtio_device *vdev)
700 for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
702 case VIRTIO_RING_F_INDIRECT_DESC:
704 case VIRTIO_RING_F_EVENT_IDX:
707 /* We don't understand this bit. */
708 clear_bit(i, vdev->features);
712 EXPORT_SYMBOL_GPL(vring_transport_features);
715 * virtqueue_get_vring_size - return the size of the virtqueue's vring
716 * @vq: the struct virtqueue containing the vring of interest.
718 * Returns the size of the vring. This is mainly used for boasting to
719 * userspace. Unlike other operations, this need not be serialized.
721 unsigned int virtqueue_get_vring_size(struct virtqueue *_vq)
724 struct vring_virtqueue *vq = to_vvq(_vq);
726 return vq->vring.num;
728 EXPORT_SYMBOL_GPL(virtqueue_get_vring_size);
730 MODULE_LICENSE("GPL");