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. */ 110 static int vring_add_indirect(struct vring_virtqueue *vq, 111 struct scatterlist sg[], 112 unsigned int out, 113 unsigned int in) 114 { 115 struct vring_desc *desc; 116 unsigned head; 117 int i; 118 119 desc = kmalloc((out + in) * sizeof(struct vring_desc), GFP_ATOMIC); 120 if (!desc) 121 return vq->vring.num; 122 123 /* Transfer entries from the sg list into the indirect page */ 124 for (i = 0; i < out; i++) { 125 desc[i].flags = VRING_DESC_F_NEXT; 126 desc[i].addr = sg_phys(sg); 127 desc[i].len = sg->length; 128 desc[i].next = i+1; 129 sg++; 130 } 131 for (; i < (out + in); i++) { 132 desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE; 133 desc[i].addr = sg_phys(sg); 134 desc[i].len = sg->length; 135 desc[i].next = i+1; 136 sg++; 137 } 138 139 /* Last one doesn't continue. */ 140 desc[i-1].flags &= ~VRING_DESC_F_NEXT; 141 desc[i-1].next = 0; 142 143 /* We're about to use a buffer */ 144 vq->num_free--; 145 146 /* Use a single buffer which doesn't continue */ 147 head = vq->free_head; 148 vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT; 149 vq->vring.desc[head].addr = virt_to_phys(desc); 150 vq->vring.desc[head].len = i * sizeof(struct vring_desc); 151 152 /* Update free pointer */ 153 vq->free_head = vq->vring.desc[head].next; 154 155 return head; 156 } 157 158 static int vring_add_buf(struct virtqueue *_vq, 159 struct scatterlist sg[], 160 unsigned int out, 161 unsigned int in, 162 void *data) 163 { 164 struct vring_virtqueue *vq = to_vvq(_vq); 165 unsigned int i, avail, head, uninitialized_var(prev); 166 167 START_USE(vq); 168 169 BUG_ON(data == NULL); 170 171 /* If the host supports indirect descriptor tables, and we have multiple 172 * buffers, then go indirect. FIXME: tune this threshold */ 173 if (vq->indirect && (out + in) > 1 && vq->num_free) { 174 head = vring_add_indirect(vq, sg, out, in); 175 if (head != vq->vring.num) 176 goto add_head; 177 } 178 179 BUG_ON(out + in > vq->vring.num); 180 BUG_ON(out + in == 0); 181 182 if (vq->num_free < out + in) { 183 pr_debug("Can't add buf len %i - avail = %i\n", 184 out + in, vq->num_free); 185 /* FIXME: for historical reasons, we force a notify here if 186 * there are outgoing parts to the buffer. Presumably the 187 * host should service the ring ASAP. */ 188 if (out) 189 vq->notify(&vq->vq); 190 END_USE(vq); 191 return -ENOSPC; 192 } 193 194 /* We're about to use some buffers from the free list. */ 195 vq->num_free -= out + in; 196 197 head = vq->free_head; 198 for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) { 199 vq->vring.desc[i].flags = VRING_DESC_F_NEXT; 200 vq->vring.desc[i].addr = sg_phys(sg); 201 vq->vring.desc[i].len = sg->length; 202 prev = i; 203 sg++; 204 } 205 for (; in; i = vq->vring.desc[i].next, in--) { 206 vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE; 207 vq->vring.desc[i].addr = sg_phys(sg); 208 vq->vring.desc[i].len = sg->length; 209 prev = i; 210 sg++; 211 } 212 /* Last one doesn't continue. */ 213 vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT; 214 215 /* Update free pointer */ 216 vq->free_head = i; 217 218 add_head: 219 /* Set token. */ 220 vq->data[head] = data; 221 222 /* Put entry in available array (but don't update avail->idx until they 223 * do sync). FIXME: avoid modulus here? */ 224 avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num; 225 vq->vring.avail->ring[avail] = head; 226 227 pr_debug("Added buffer head %i to %p\n", head, vq); 228 END_USE(vq); 229 230 /* If we're indirect, we can fit many (assuming not OOM). */ 231 if (vq->indirect) 232 return vq->num_free ? vq->vring.num : 0; 233 return vq->num_free; 234 } 235 236 static void vring_kick(struct virtqueue *_vq) 237 { 238 struct vring_virtqueue *vq = to_vvq(_vq); 239 START_USE(vq); 240 /* Descriptors and available array need to be set before we expose the 241 * new available array entries. */ 242 virtio_wmb(); 243 244 vq->vring.avail->idx += vq->num_added; 245 vq->num_added = 0; 246 247 /* Need to update avail index before checking if we should notify */ 248 virtio_mb(); 249 250 if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) 251 /* Prod other side to tell it about changes. */ 252 vq->notify(&vq->vq); 253 254 END_USE(vq); 255 } 256 257 static void detach_buf(struct vring_virtqueue *vq, unsigned int head) 258 { 259 unsigned int i; 260 261 /* Clear data ptr. */ 262 vq->data[head] = NULL; 263 264 /* Put back on free list: find end */ 265 i = head; 266 267 /* Free the indirect table */ 268 if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT) 269 kfree(phys_to_virt(vq->vring.desc[i].addr)); 270 271 while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) { 272 i = vq->vring.desc[i].next; 273 vq->num_free++; 274 } 275 276 vq->vring.desc[i].next = vq->free_head; 277 vq->free_head = head; 278 /* Plus final descriptor */ 279 vq->num_free++; 280 } 281 282 static inline bool more_used(const struct vring_virtqueue *vq) 283 { 284 return vq->last_used_idx != vq->vring.used->idx; 285 } 286 287 static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len) 288 { 289 struct vring_virtqueue *vq = to_vvq(_vq); 290 void *ret; 291 unsigned int i; 292 293 START_USE(vq); 294 295 if (unlikely(vq->broken)) { 296 END_USE(vq); 297 return NULL; 298 } 299 300 if (!more_used(vq)) { 301 pr_debug("No more buffers in queue\n"); 302 END_USE(vq); 303 return NULL; 304 } 305 306 /* Only get used array entries after they have been exposed by host. */ 307 virtio_rmb(); 308 309 i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id; 310 *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len; 311 312 if (unlikely(i >= vq->vring.num)) { 313 BAD_RING(vq, "id %u out of range\n", i); 314 return NULL; 315 } 316 if (unlikely(!vq->data[i])) { 317 BAD_RING(vq, "id %u is not a head!\n", i); 318 return NULL; 319 } 320 321 /* detach_buf clears data, so grab it now. */ 322 ret = vq->data[i]; 323 detach_buf(vq, i); 324 vq->last_used_idx++; 325 END_USE(vq); 326 return ret; 327 } 328 329 static void vring_disable_cb(struct virtqueue *_vq) 330 { 331 struct vring_virtqueue *vq = to_vvq(_vq); 332 333 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; 334 } 335 336 static bool vring_enable_cb(struct virtqueue *_vq) 337 { 338 struct vring_virtqueue *vq = to_vvq(_vq); 339 340 START_USE(vq); 341 342 /* We optimistically turn back on interrupts, then check if there was 343 * more to do. */ 344 vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; 345 virtio_mb(); 346 if (unlikely(more_used(vq))) { 347 END_USE(vq); 348 return false; 349 } 350 351 END_USE(vq); 352 return true; 353 } 354 355 static void *vring_detach_unused_buf(struct virtqueue *_vq) 356 { 357 struct vring_virtqueue *vq = to_vvq(_vq); 358 unsigned int i; 359 void *buf; 360 361 START_USE(vq); 362 363 for (i = 0; i < vq->vring.num; i++) { 364 if (!vq->data[i]) 365 continue; 366 /* detach_buf clears data, so grab it now. */ 367 buf = vq->data[i]; 368 detach_buf(vq, i); 369 END_USE(vq); 370 return buf; 371 } 372 /* That should have freed everything. */ 373 BUG_ON(vq->num_free != vq->vring.num); 374 375 END_USE(vq); 376 return NULL; 377 } 378 379 irqreturn_t vring_interrupt(int irq, void *_vq) 380 { 381 struct vring_virtqueue *vq = to_vvq(_vq); 382 383 if (!more_used(vq)) { 384 pr_debug("virtqueue interrupt with no work for %p\n", vq); 385 return IRQ_NONE; 386 } 387 388 if (unlikely(vq->broken)) 389 return IRQ_HANDLED; 390 391 pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); 392 if (vq->vq.callback) 393 vq->vq.callback(&vq->vq); 394 395 return IRQ_HANDLED; 396 } 397 EXPORT_SYMBOL_GPL(vring_interrupt); 398 399 static struct virtqueue_ops vring_vq_ops = { 400 .add_buf = vring_add_buf, 401 .get_buf = vring_get_buf, 402 .kick = vring_kick, 403 .disable_cb = vring_disable_cb, 404 .enable_cb = vring_enable_cb, 405 .detach_unused_buf = vring_detach_unused_buf, 406 }; 407 408 struct virtqueue *vring_new_virtqueue(unsigned int num, 409 unsigned int vring_align, 410 struct virtio_device *vdev, 411 void *pages, 412 void (*notify)(struct virtqueue *), 413 void (*callback)(struct virtqueue *), 414 const char *name) 415 { 416 struct vring_virtqueue *vq; 417 unsigned int i; 418 419 /* We assume num is a power of 2. */ 420 if (num & (num - 1)) { 421 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num); 422 return NULL; 423 } 424 425 vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL); 426 if (!vq) 427 return NULL; 428 429 vring_init(&vq->vring, num, pages, vring_align); 430 vq->vq.callback = callback; 431 vq->vq.vdev = vdev; 432 vq->vq.vq_ops = &vring_vq_ops; 433 vq->vq.name = name; 434 vq->notify = notify; 435 vq->broken = false; 436 vq->last_used_idx = 0; 437 vq->num_added = 0; 438 list_add_tail(&vq->vq.list, &vdev->vqs); 439 #ifdef DEBUG 440 vq->in_use = false; 441 #endif 442 443 vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC); 444 445 /* No callback? Tell other side not to bother us. */ 446 if (!callback) 447 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; 448 449 /* Put everything in free lists. */ 450 vq->num_free = num; 451 vq->free_head = 0; 452 for (i = 0; i < num-1; i++) { 453 vq->vring.desc[i].next = i+1; 454 vq->data[i] = NULL; 455 } 456 vq->data[i] = NULL; 457 458 return &vq->vq; 459 } 460 EXPORT_SYMBOL_GPL(vring_new_virtqueue); 461 462 void vring_del_virtqueue(struct virtqueue *vq) 463 { 464 list_del(&vq->list); 465 kfree(to_vvq(vq)); 466 } 467 EXPORT_SYMBOL_GPL(vring_del_virtqueue); 468 469 /* Manipulates transport-specific feature bits. */ 470 void vring_transport_features(struct virtio_device *vdev) 471 { 472 unsigned int i; 473 474 for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) { 475 switch (i) { 476 case VIRTIO_RING_F_INDIRECT_DESC: 477 break; 478 default: 479 /* We don't understand this bit. */ 480 clear_bit(i, vdev->features); 481 } 482 } 483 } 484 EXPORT_SYMBOL_GPL(vring_transport_features); 485 486 MODULE_LICENSE("GPL"); 487