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>
24 /* virtio guest is communicating with a virtual "device" that actually runs on
25 * a host processor. Memory barriers are used to control SMP effects. */
27 /* Where possible, use SMP barriers which are more lightweight than mandatory
28 * barriers, because mandatory barriers control MMIO effects on accesses
29 * through relaxed memory I/O windows (which virtio does not use). */
30 #define virtio_mb() smp_mb()
31 #define virtio_rmb() smp_rmb()
32 #define virtio_wmb() smp_wmb()
34 /* We must force memory ordering even if guest is UP since host could be
35 * running on another CPU, but SMP barriers are defined to barrier() in that
36 * configuration. So fall back to mandatory barriers instead. */
37 #define virtio_mb() mb()
38 #define virtio_rmb() rmb()
39 #define virtio_wmb() wmb()
43 /* For development, we want to crash whenever the ring is screwed. */
44 #define BAD_RING(_vq, fmt, args...) \
46 dev_err(&(_vq)->vq.vdev->dev, \
47 "%s:"fmt, (_vq)->vq.name, ##args); \
50 /* Caller is supposed to guarantee no reentry. */
51 #define START_USE(_vq) \
54 panic("%s:in_use = %i\n", \
55 (_vq)->vq.name, (_vq)->in_use); \
56 (_vq)->in_use = __LINE__; \
58 #define END_USE(_vq) \
59 do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
61 #define BAD_RING(_vq, fmt, args...) \
63 dev_err(&_vq->vq.vdev->dev, \
64 "%s:"fmt, (_vq)->vq.name, ##args); \
65 (_vq)->broken = true; \
71 struct vring_virtqueue
75 /* Actual memory layout for this queue */
78 /* Other side has made a mess, don't try any more. */
81 /* Host supports indirect buffers */
84 /* Number of free buffers */
85 unsigned int num_free;
86 /* Head of free buffer list. */
87 unsigned int free_head;
88 /* Number we've added since last sync. */
89 unsigned int num_added;
91 /* Last used index we've seen. */
94 /* How to notify other side. FIXME: commonalize hcalls! */
95 void (*notify)(struct virtqueue *vq);
98 /* They're supposed to lock for us. */
102 /* Tokens for callbacks. */
106 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
108 /* Set up an indirect table of descriptors and add it to the queue. */
109 static int vring_add_indirect(struct vring_virtqueue *vq,
110 struct scatterlist sg[],
114 struct vring_desc *desc;
118 desc = kmalloc((out + in) * sizeof(struct vring_desc), GFP_ATOMIC);
120 return vq->vring.num;
122 /* Transfer entries from the sg list into the indirect page */
123 for (i = 0; i < out; i++) {
124 desc[i].flags = VRING_DESC_F_NEXT;
125 desc[i].addr = sg_phys(sg);
126 desc[i].len = sg->length;
130 for (; i < (out + in); i++) {
131 desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
132 desc[i].addr = sg_phys(sg);
133 desc[i].len = sg->length;
138 /* Last one doesn't continue. */
139 desc[i-1].flags &= ~VRING_DESC_F_NEXT;
142 /* We're about to use a buffer */
145 /* Use a single buffer which doesn't continue */
146 head = vq->free_head;
147 vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
148 vq->vring.desc[head].addr = virt_to_phys(desc);
149 vq->vring.desc[head].len = i * sizeof(struct vring_desc);
151 /* Update free pointer */
152 vq->free_head = vq->vring.desc[head].next;
157 static int vring_add_buf(struct virtqueue *_vq,
158 struct scatterlist sg[],
163 struct vring_virtqueue *vq = to_vvq(_vq);
164 unsigned int i, avail, head, uninitialized_var(prev);
168 BUG_ON(data == NULL);
170 /* If the host supports indirect descriptor tables, and we have multiple
171 * buffers, then go indirect. FIXME: tune this threshold */
172 if (vq->indirect && (out + in) > 1 && vq->num_free) {
173 head = vring_add_indirect(vq, sg, out, in);
174 if (head != vq->vring.num)
178 BUG_ON(out + in > vq->vring.num);
179 BUG_ON(out + in == 0);
181 if (vq->num_free < out + in) {
182 pr_debug("Can't add buf len %i - avail = %i\n",
183 out + in, vq->num_free);
184 /* FIXME: for historical reasons, we force a notify here if
185 * there are outgoing parts to the buffer. Presumably the
186 * host should service the ring ASAP. */
193 /* We're about to use some buffers from the free list. */
194 vq->num_free -= out + in;
196 head = vq->free_head;
197 for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
198 vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
199 vq->vring.desc[i].addr = sg_phys(sg);
200 vq->vring.desc[i].len = sg->length;
204 for (; in; i = vq->vring.desc[i].next, in--) {
205 vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
206 vq->vring.desc[i].addr = sg_phys(sg);
207 vq->vring.desc[i].len = sg->length;
211 /* Last one doesn't continue. */
212 vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
214 /* Update free pointer */
219 vq->data[head] = data;
221 /* Put entry in available array (but don't update avail->idx until they
222 * do sync). FIXME: avoid modulus here? */
223 avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
224 vq->vring.avail->ring[avail] = head;
226 pr_debug("Added buffer head %i to %p\n", head, vq);
229 /* If we're indirect, we can fit many (assuming not OOM). */
231 return vq->num_free ? vq->vring.num : 0;
235 static void vring_kick(struct virtqueue *_vq)
237 struct vring_virtqueue *vq = to_vvq(_vq);
239 /* Descriptors and available array need to be set before we expose the
240 * new available array entries. */
243 vq->vring.avail->idx += vq->num_added;
246 /* Need to update avail index before checking if we should notify */
249 if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
250 /* Prod other side to tell it about changes. */
256 static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
260 /* Clear data ptr. */
261 vq->data[head] = NULL;
263 /* Put back on free list: find end */
266 /* Free the indirect table */
267 if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
268 kfree(phys_to_virt(vq->vring.desc[i].addr));
270 while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
271 i = vq->vring.desc[i].next;
275 vq->vring.desc[i].next = vq->free_head;
276 vq->free_head = head;
277 /* Plus final descriptor */
281 static inline bool more_used(const struct vring_virtqueue *vq)
283 return vq->last_used_idx != vq->vring.used->idx;
286 static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len)
288 struct vring_virtqueue *vq = to_vvq(_vq);
294 if (unlikely(vq->broken)) {
299 if (!more_used(vq)) {
300 pr_debug("No more buffers in queue\n");
305 /* Only get used array entries after they have been exposed by host. */
308 i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
309 *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
311 if (unlikely(i >= vq->vring.num)) {
312 BAD_RING(vq, "id %u out of range\n", i);
315 if (unlikely(!vq->data[i])) {
316 BAD_RING(vq, "id %u is not a head!\n", i);
320 /* detach_buf clears data, so grab it now. */
328 static void vring_disable_cb(struct virtqueue *_vq)
330 struct vring_virtqueue *vq = to_vvq(_vq);
332 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
335 static bool vring_enable_cb(struct virtqueue *_vq)
337 struct vring_virtqueue *vq = to_vvq(_vq);
341 /* We optimistically turn back on interrupts, then check if there was
343 vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
345 if (unlikely(more_used(vq))) {
354 static void *vring_detach_unused_buf(struct virtqueue *_vq)
356 struct vring_virtqueue *vq = to_vvq(_vq);
362 for (i = 0; i < vq->vring.num; i++) {
365 /* detach_buf clears data, so grab it now. */
371 /* That should have freed everything. */
372 BUG_ON(vq->num_free != vq->vring.num);
378 irqreturn_t vring_interrupt(int irq, void *_vq)
380 struct vring_virtqueue *vq = to_vvq(_vq);
382 if (!more_used(vq)) {
383 pr_debug("virtqueue interrupt with no work for %p\n", vq);
387 if (unlikely(vq->broken))
390 pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
392 vq->vq.callback(&vq->vq);
396 EXPORT_SYMBOL_GPL(vring_interrupt);
398 static struct virtqueue_ops vring_vq_ops = {
399 .add_buf = vring_add_buf,
400 .get_buf = vring_get_buf,
402 .disable_cb = vring_disable_cb,
403 .enable_cb = vring_enable_cb,
404 .detach_unused_buf = vring_detach_unused_buf,
407 struct virtqueue *vring_new_virtqueue(unsigned int num,
408 unsigned int vring_align,
409 struct virtio_device *vdev,
411 void (*notify)(struct virtqueue *),
412 void (*callback)(struct virtqueue *),
415 struct vring_virtqueue *vq;
418 /* We assume num is a power of 2. */
419 if (num & (num - 1)) {
420 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
424 vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
428 vring_init(&vq->vring, num, pages, vring_align);
429 vq->vq.callback = callback;
431 vq->vq.vq_ops = &vring_vq_ops;
435 vq->last_used_idx = 0;
437 list_add_tail(&vq->vq.list, &vdev->vqs);
442 vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
444 /* No callback? Tell other side not to bother us. */
446 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
448 /* Put everything in free lists. */
451 for (i = 0; i < num-1; i++) {
452 vq->vring.desc[i].next = i+1;
459 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
461 void vring_del_virtqueue(struct virtqueue *vq)
466 EXPORT_SYMBOL_GPL(vring_del_virtqueue);
468 /* Manipulates transport-specific feature bits. */
469 void vring_transport_features(struct virtio_device *vdev)
473 for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
475 case VIRTIO_RING_F_INDIRECT_DESC:
478 /* We don't understand this bit. */
479 clear_bit(i, vdev->features);
483 EXPORT_SYMBOL_GPL(vring_transport_features);
485 MODULE_LICENSE("GPL");