1 /* Virtio ring implementation.
2 *
3 * Copyright 2007 Rusty Russell IBM Corporation
4 *
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.
9 *
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.
14 *
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
18 */
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
25 /* virtio guest is communicating with a virtual "device" that actually runs on
26 * a host processor. Memory barriers are used to control SMP effects. */
27 #ifdef CONFIG_SMP
28 /* Where possible, use SMP barriers which are more lightweight than mandatory
29 * barriers, because mandatory barriers control MMIO effects on accesses
30 * through relaxed memory I/O windows (which virtio does not use). */
31 #define virtio_mb() smp_mb()
32 #define virtio_rmb() smp_rmb()
33 #define virtio_wmb() smp_wmb()
34 #else
35 /* We must force memory ordering even if guest is UP since host could be
36 * running on another CPU, but SMP barriers are defined to barrier() in that
37 * configuration. So fall back to mandatory barriers instead. */
38 #define virtio_mb() mb()
39 #define virtio_rmb() rmb()
40 #define virtio_wmb() wmb()
41 #endif
42
43 #ifdef DEBUG
44 /* For development, we want to crash whenever the ring is screwed. */
45 #define BAD_RING(_vq, fmt, args...) \
46 do { \
47 dev_err(&(_vq)->vq.vdev->dev, \
48 "%s:"fmt, (_vq)->vq.name, ##args); \
49 BUG(); \
50 } while (0)
51 /* Caller is supposed to guarantee no reentry. */
52 #define START_USE(_vq) \
53 do { \
54 if ((_vq)->in_use) \
55 panic("%s:in_use = %i\n", \
56 (_vq)->vq.name, (_vq)->in_use); \
57 (_vq)->in_use = __LINE__; \
58 } while (0)
59 #define END_USE(_vq) \
60 do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
61 #else
62 #define BAD_RING(_vq, fmt, args...) \
63 do { \
64 dev_err(&_vq->vq.vdev->dev, \
65 "%s:"fmt, (_vq)->vq.name, ##args); \
66 (_vq)->broken = true; \
67 } while (0)
68 #define START_USE(vq)
69 #define END_USE(vq)
70 #endif
71
72 struct vring_virtqueue
73 {
74 struct virtqueue vq;
75
76 /* Actual memory layout for this queue */
77 struct vring vring;
78
79 /* Other side has made a mess, don't try any more. */
80 bool broken;
81
82 /* Host supports indirect buffers */
83 bool indirect;
84
85 /* Number of free buffers */
86 unsigned int num_free;
87 /* Head of free buffer list. */
88 unsigned int free_head;
89 /* Number we've added since last sync. */
90 unsigned int num_added;
91
92 /* Last used index we've seen. */
93 u16 last_used_idx;
94
95 /* How to notify other side. FIXME: commonalize hcalls! */
96 void (*notify)(struct virtqueue *vq);
97
98 #ifdef DEBUG
99 /* They're supposed to lock for us. */
100 unsigned int in_use;
101 #endif
102
103 /* Tokens for callbacks. */
104 void *data[];
105 };
106
107 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
108
109 /* Set up an indirect table of descriptors and add it to the queue. */
vring_add_indirect(struct vring_virtqueue * vq,struct scatterlist sg[],unsigned int out,unsigned int in,gfp_t gfp)110 static int vring_add_indirect(struct vring_virtqueue *vq,
111 struct scatterlist sg[],
112 unsigned int out,
113 unsigned int in,
114 gfp_t gfp)
115 {
116 struct vring_desc *desc;
117 unsigned head;
118 int i;
119
120 desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
121 if (!desc)
122 return -ENOMEM;
123
124 /* Transfer entries from the sg list into the indirect page */
125 for (i = 0; i < out; i++) {
126 desc[i].flags = VRING_DESC_F_NEXT;
127 desc[i].addr = sg_phys(sg);
128 desc[i].len = sg->length;
129 desc[i].next = i+1;
130 sg++;
131 }
132 for (; i < (out + in); i++) {
133 desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
134 desc[i].addr = sg_phys(sg);
135 desc[i].len = sg->length;
136 desc[i].next = i+1;
137 sg++;
138 }
139
140 /* Last one doesn't continue. */
141 desc[i-1].flags &= ~VRING_DESC_F_NEXT;
142 desc[i-1].next = 0;
143
144 /* We're about to use a buffer */
145 vq->num_free--;
146
147 /* Use a single buffer which doesn't continue */
148 head = vq->free_head;
149 vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
150 vq->vring.desc[head].addr = virt_to_phys(desc);
151 vq->vring.desc[head].len = i * sizeof(struct vring_desc);
152
153 /* Update free pointer */
154 vq->free_head = vq->vring.desc[head].next;
155
156 return head;
157 }
158
virtqueue_add_buf_gfp(struct virtqueue * _vq,struct scatterlist sg[],unsigned int out,unsigned int in,void * data,gfp_t gfp)159 int virtqueue_add_buf_gfp(struct virtqueue *_vq,
160 struct scatterlist sg[],
161 unsigned int out,
162 unsigned int in,
163 void *data,
164 gfp_t gfp)
165 {
166 struct vring_virtqueue *vq = to_vvq(_vq);
167 unsigned int i, avail, uninitialized_var(prev);
168 int head;
169
170 START_USE(vq);
171
172 BUG_ON(data == NULL);
173
174 /* If the host supports indirect descriptor tables, and we have multiple
175 * buffers, then go indirect. FIXME: tune this threshold */
176 if (vq->indirect && (out + in) > 1 && vq->num_free) {
177 head = vring_add_indirect(vq, sg, out, in, gfp);
178 if (likely(head >= 0))
179 goto add_head;
180 }
181
182 BUG_ON(out + in > vq->vring.num);
183 BUG_ON(out + in == 0);
184
185 if (vq->num_free < out + in) {
186 pr_debug("Can't add buf len %i - avail = %i\n",
187 out + in, vq->num_free);
188 /* FIXME: for historical reasons, we force a notify here if
189 * there are outgoing parts to the buffer. Presumably the
190 * host should service the ring ASAP. */
191 if (out)
192 vq->notify(&vq->vq);
193 END_USE(vq);
194 return -ENOSPC;
195 }
196
197 /* We're about to use some buffers from the free list. */
198 vq->num_free -= out + in;
199
200 head = vq->free_head;
201 for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
202 vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
203 vq->vring.desc[i].addr = sg_phys(sg);
204 vq->vring.desc[i].len = sg->length;
205 prev = i;
206 sg++;
207 }
208 for (; in; i = vq->vring.desc[i].next, in--) {
209 vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
210 vq->vring.desc[i].addr = sg_phys(sg);
211 vq->vring.desc[i].len = sg->length;
212 prev = i;
213 sg++;
214 }
215 /* Last one doesn't continue. */
216 vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
217
218 /* Update free pointer */
219 vq->free_head = i;
220
221 add_head:
222 /* Set token. */
223 vq->data[head] = data;
224
225 /* Put entry in available array (but don't update avail->idx until they
226 * do sync). FIXME: avoid modulus here? */
227 avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
228 vq->vring.avail->ring[avail] = head;
229
230 pr_debug("Added buffer head %i to %p\n", head, vq);
231 END_USE(vq);
232
233 return vq->num_free;
234 }
235 EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);
236
virtqueue_kick(struct virtqueue * _vq)237 void virtqueue_kick(struct virtqueue *_vq)
238 {
239 struct vring_virtqueue *vq = to_vvq(_vq);
240 START_USE(vq);
241 /* Descriptors and available array need to be set before we expose the
242 * new available array entries. */
243 virtio_wmb();
244
245 vq->vring.avail->idx += vq->num_added;
246 vq->num_added = 0;
247
248 /* Need to update avail index before checking if we should notify */
249 virtio_mb();
250
251 if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
252 /* Prod other side to tell it about changes. */
253 vq->notify(&vq->vq);
254
255 END_USE(vq);
256 }
257 EXPORT_SYMBOL_GPL(virtqueue_kick);
258
detach_buf(struct vring_virtqueue * vq,unsigned int head)259 static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
260 {
261 unsigned int i;
262
263 /* Clear data ptr. */
264 vq->data[head] = NULL;
265
266 /* Put back on free list: find end */
267 i = head;
268
269 /* Free the indirect table */
270 if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
271 kfree(phys_to_virt(vq->vring.desc[i].addr));
272
273 while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
274 i = vq->vring.desc[i].next;
275 vq->num_free++;
276 }
277
278 vq->vring.desc[i].next = vq->free_head;
279 vq->free_head = head;
280 /* Plus final descriptor */
281 vq->num_free++;
282 }
283
more_used(const struct vring_virtqueue * vq)284 static inline bool more_used(const struct vring_virtqueue *vq)
285 {
286 return vq->last_used_idx != vq->vring.used->idx;
287 }
288
virtqueue_get_buf(struct virtqueue * _vq,unsigned int * len)289 void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
290 {
291 struct vring_virtqueue *vq = to_vvq(_vq);
292 void *ret;
293 unsigned int i;
294
295 START_USE(vq);
296
297 if (unlikely(vq->broken)) {
298 END_USE(vq);
299 return NULL;
300 }
301
302 if (!more_used(vq)) {
303 pr_debug("No more buffers in queue\n");
304 END_USE(vq);
305 return NULL;
306 }
307
308 /* Only get used array entries after they have been exposed by host. */
309 virtio_rmb();
310
311 i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
312 *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
313
314 if (unlikely(i >= vq->vring.num)) {
315 BAD_RING(vq, "id %u out of range\n", i);
316 return NULL;
317 }
318 if (unlikely(!vq->data[i])) {
319 BAD_RING(vq, "id %u is not a head!\n", i);
320 return NULL;
321 }
322
323 /* detach_buf clears data, so grab it now. */
324 ret = vq->data[i];
325 detach_buf(vq, i);
326 vq->last_used_idx++;
327 END_USE(vq);
328 return ret;
329 }
330 EXPORT_SYMBOL_GPL(virtqueue_get_buf);
331
virtqueue_disable_cb(struct virtqueue * _vq)332 void virtqueue_disable_cb(struct virtqueue *_vq)
333 {
334 struct vring_virtqueue *vq = to_vvq(_vq);
335
336 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
337 }
338 EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
339
virtqueue_enable_cb(struct virtqueue * _vq)340 bool virtqueue_enable_cb(struct virtqueue *_vq)
341 {
342 struct vring_virtqueue *vq = to_vvq(_vq);
343
344 START_USE(vq);
345
346 /* We optimistically turn back on interrupts, then check if there was
347 * more to do. */
348 vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
349 virtio_mb();
350 if (unlikely(more_used(vq))) {
351 END_USE(vq);
352 return false;
353 }
354
355 END_USE(vq);
356 return true;
357 }
358 EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
359
virtqueue_detach_unused_buf(struct virtqueue * _vq)360 void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
361 {
362 struct vring_virtqueue *vq = to_vvq(_vq);
363 unsigned int i;
364 void *buf;
365
366 START_USE(vq);
367
368 for (i = 0; i < vq->vring.num; i++) {
369 if (!vq->data[i])
370 continue;
371 /* detach_buf clears data, so grab it now. */
372 buf = vq->data[i];
373 detach_buf(vq, i);
374 vq->vring.avail->idx--;
375 END_USE(vq);
376 return buf;
377 }
378 /* That should have freed everything. */
379 BUG_ON(vq->num_free != vq->vring.num);
380
381 END_USE(vq);
382 return NULL;
383 }
384 EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
385
vring_interrupt(int irq,void * _vq)386 irqreturn_t vring_interrupt(int irq, void *_vq)
387 {
388 struct vring_virtqueue *vq = to_vvq(_vq);
389
390 if (!more_used(vq)) {
391 pr_debug("virtqueue interrupt with no work for %p\n", vq);
392 return IRQ_NONE;
393 }
394
395 if (unlikely(vq->broken))
396 return IRQ_HANDLED;
397
398 pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
399 if (vq->vq.callback)
400 vq->vq.callback(&vq->vq);
401
402 return IRQ_HANDLED;
403 }
404 EXPORT_SYMBOL_GPL(vring_interrupt);
405
vring_new_virtqueue(unsigned int num,unsigned int vring_align,struct virtio_device * vdev,void * pages,void (* notify)(struct virtqueue *),void (* callback)(struct virtqueue *),const char * name)406 struct virtqueue *vring_new_virtqueue(unsigned int num,
407 unsigned int vring_align,
408 struct virtio_device *vdev,
409 void *pages,
410 void (*notify)(struct virtqueue *),
411 void (*callback)(struct virtqueue *),
412 const char *name)
413 {
414 struct vring_virtqueue *vq;
415 unsigned int i;
416
417 /* We assume num is a power of 2. */
418 if (num & (num - 1)) {
419 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
420 return NULL;
421 }
422
423 vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
424 if (!vq)
425 return NULL;
426
427 vring_init(&vq->vring, num, pages, vring_align);
428 vq->vq.callback = callback;
429 vq->vq.vdev = vdev;
430 vq->vq.name = name;
431 vq->notify = notify;
432 vq->broken = false;
433 vq->last_used_idx = 0;
434 vq->num_added = 0;
435 list_add_tail(&vq->vq.list, &vdev->vqs);
436 #ifdef DEBUG
437 vq->in_use = false;
438 #endif
439
440 vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
441
442 /* No callback? Tell other side not to bother us. */
443 if (!callback)
444 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
445
446 /* Put everything in free lists. */
447 vq->num_free = num;
448 vq->free_head = 0;
449 for (i = 0; i < num-1; i++) {
450 vq->vring.desc[i].next = i+1;
451 vq->data[i] = NULL;
452 }
453 vq->data[i] = NULL;
454
455 return &vq->vq;
456 }
457 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
458
vring_del_virtqueue(struct virtqueue * vq)459 void vring_del_virtqueue(struct virtqueue *vq)
460 {
461 list_del(&vq->list);
462 kfree(to_vvq(vq));
463 }
464 EXPORT_SYMBOL_GPL(vring_del_virtqueue);
465
466 /* Manipulates transport-specific feature bits. */
vring_transport_features(struct virtio_device * vdev)467 void vring_transport_features(struct virtio_device *vdev)
468 {
469 unsigned int i;
470
471 for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
472 switch (i) {
473 case VIRTIO_RING_F_INDIRECT_DESC:
474 break;
475 default:
476 /* We don't understand this bit. */
477 clear_bit(i, vdev->features);
478 }
479 }
480 }
481 EXPORT_SYMBOL_GPL(vring_transport_features);
482
483 MODULE_LICENSE("GPL");
484