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 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. */ 26 #ifdef CONFIG_SMP 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() 33 #else 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() 40 #endif 41 42 #ifdef DEBUG 43 /* For development, we want to crash whenever the ring is screwed. */ 44 #define BAD_RING(_vq, fmt, args...) \ 45 do { \ 46 dev_err(&(_vq)->vq.vdev->dev, \ 47 "%s:"fmt, (_vq)->vq.name, ##args); \ 48 BUG(); \ 49 } while (0) 50 /* Caller is supposed to guarantee no reentry. */ 51 #define START_USE(_vq) \ 52 do { \ 53 if ((_vq)->in_use) \ 54 panic("%s:in_use = %i\n", \ 55 (_vq)->vq.name, (_vq)->in_use); \ 56 (_vq)->in_use = __LINE__; \ 57 } while (0) 58 #define END_USE(_vq) \ 59 do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0) 60 #else 61 #define BAD_RING(_vq, fmt, args...) \ 62 do { \ 63 dev_err(&_vq->vq.vdev->dev, \ 64 "%s:"fmt, (_vq)->vq.name, ##args); \ 65 (_vq)->broken = true; \ 66 } while (0) 67 #define START_USE(vq) 68 #define END_USE(vq) 69 #endif 70 71 struct vring_virtqueue 72 { 73 struct virtqueue vq; 74 75 /* Actual memory layout for this queue */ 76 struct vring vring; 77 78 /* Other side has made a mess, don't try any more. */ 79 bool broken; 80 81 /* Host supports indirect buffers */ 82 bool indirect; 83 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; 90 91 /* Last used index we've seen. */ 92 u16 last_used_idx; 93 94 /* How to notify other side. FIXME: commonalize hcalls! */ 95 void (*notify)(struct virtqueue *vq); 96 97 #ifdef DEBUG 98 /* They're supposed to lock for us. */ 99 unsigned int in_use; 100 #endif 101 102 /* Tokens for callbacks. */ 103 void *data[]; 104 }; 105 106 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq) 107 108 /* 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[], 111 unsigned int out, 112 unsigned int in) 113 { 114 struct vring_desc *desc; 115 unsigned head; 116 int i; 117 118 desc = kmalloc((out + in) * sizeof(struct vring_desc), GFP_ATOMIC); 119 if (!desc) 120 return vq->vring.num; 121 122 /* 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; 127 desc[i].next = i+1; 128 sg++; 129 } 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; 134 desc[i].next = i+1; 135 sg++; 136 } 137 138 /* Last one doesn't continue. */ 139 desc[i-1].flags &= ~VRING_DESC_F_NEXT; 140 desc[i-1].next = 0; 141 142 /* We're about to use a buffer */ 143 vq->num_free--; 144 145 /* 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); 150 151 /* Update free pointer */ 152 vq->free_head = vq->vring.desc[head].next; 153 154 return head; 155 } 156 157 static int vring_add_buf(struct virtqueue *_vq, 158 struct scatterlist sg[], 159 unsigned int out, 160 unsigned int in, 161 void *data) 162 { 163 struct vring_virtqueue *vq = to_vvq(_vq); 164 unsigned int i, avail, head, uninitialized_var(prev); 165 166 START_USE(vq); 167 168 BUG_ON(data == NULL); 169 170 /* 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) 175 goto add_head; 176 } 177 178 BUG_ON(out + in > vq->vring.num); 179 BUG_ON(out + in == 0); 180 181 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. */ 187 if (out) 188 vq->notify(&vq->vq); 189 END_USE(vq); 190 return -ENOSPC; 191 } 192 193 /* We're about to use some buffers from the free list. */ 194 vq->num_free -= out + in; 195 196 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; 201 prev = i; 202 sg++; 203 } 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; 208 prev = i; 209 sg++; 210 } 211 /* Last one doesn't continue. */ 212 vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT; 213 214 /* Update free pointer */ 215 vq->free_head = i; 216 217 add_head: 218 /* Set token. */ 219 vq->data[head] = data; 220 221 /* 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; 225 226 pr_debug("Added buffer head %i to %p\n", head, vq); 227 END_USE(vq); 228 229 /* If we're indirect, we can fit many (assuming not OOM). */ 230 if (vq->indirect) 231 return vq->num_free ? vq->vring.num : 0; 232 return vq->num_free; 233 } 234 235 static void vring_kick(struct virtqueue *_vq) 236 { 237 struct vring_virtqueue *vq = to_vvq(_vq); 238 START_USE(vq); 239 /* Descriptors and available array need to be set before we expose the 240 * new available array entries. */ 241 virtio_wmb(); 242 243 vq->vring.avail->idx += vq->num_added; 244 vq->num_added = 0; 245 246 /* Need to update avail index before checking if we should notify */ 247 virtio_mb(); 248 249 if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY)) 250 /* Prod other side to tell it about changes. */ 251 vq->notify(&vq->vq); 252 253 END_USE(vq); 254 } 255 256 static void detach_buf(struct vring_virtqueue *vq, unsigned int head) 257 { 258 unsigned int i; 259 260 /* Clear data ptr. */ 261 vq->data[head] = NULL; 262 263 /* Put back on free list: find end */ 264 i = head; 265 266 /* 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)); 269 270 while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) { 271 i = vq->vring.desc[i].next; 272 vq->num_free++; 273 } 274 275 vq->vring.desc[i].next = vq->free_head; 276 vq->free_head = head; 277 /* Plus final descriptor */ 278 vq->num_free++; 279 } 280 281 static inline bool more_used(const struct vring_virtqueue *vq) 282 { 283 return vq->last_used_idx != vq->vring.used->idx; 284 } 285 286 static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len) 287 { 288 struct vring_virtqueue *vq = to_vvq(_vq); 289 void *ret; 290 unsigned int i; 291 292 START_USE(vq); 293 294 if (unlikely(vq->broken)) { 295 END_USE(vq); 296 return NULL; 297 } 298 299 if (!more_used(vq)) { 300 pr_debug("No more buffers in queue\n"); 301 END_USE(vq); 302 return NULL; 303 } 304 305 /* Only get used array entries after they have been exposed by host. */ 306 virtio_rmb(); 307 308 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; 310 311 if (unlikely(i >= vq->vring.num)) { 312 BAD_RING(vq, "id %u out of range\n", i); 313 return NULL; 314 } 315 if (unlikely(!vq->data[i])) { 316 BAD_RING(vq, "id %u is not a head!\n", i); 317 return NULL; 318 } 319 320 /* detach_buf clears data, so grab it now. */ 321 ret = vq->data[i]; 322 detach_buf(vq, i); 323 vq->last_used_idx++; 324 END_USE(vq); 325 return ret; 326 } 327 328 static void vring_disable_cb(struct virtqueue *_vq) 329 { 330 struct vring_virtqueue *vq = to_vvq(_vq); 331 332 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; 333 } 334 335 static bool vring_enable_cb(struct virtqueue *_vq) 336 { 337 struct vring_virtqueue *vq = to_vvq(_vq); 338 339 START_USE(vq); 340 341 /* We optimistically turn back on interrupts, then check if there was 342 * more to do. */ 343 vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT; 344 virtio_mb(); 345 if (unlikely(more_used(vq))) { 346 END_USE(vq); 347 return false; 348 } 349 350 END_USE(vq); 351 return true; 352 } 353 354 static void *vring_detach_unused_buf(struct virtqueue *_vq) 355 { 356 struct vring_virtqueue *vq = to_vvq(_vq); 357 unsigned int i; 358 void *buf; 359 360 START_USE(vq); 361 362 for (i = 0; i < vq->vring.num; i++) { 363 if (!vq->data[i]) 364 continue; 365 /* detach_buf clears data, so grab it now. */ 366 buf = vq->data[i]; 367 detach_buf(vq, i); 368 END_USE(vq); 369 return buf; 370 } 371 /* That should have freed everything. */ 372 BUG_ON(vq->num_free != vq->vring.num); 373 374 END_USE(vq); 375 return NULL; 376 } 377 378 irqreturn_t vring_interrupt(int irq, void *_vq) 379 { 380 struct vring_virtqueue *vq = to_vvq(_vq); 381 382 if (!more_used(vq)) { 383 pr_debug("virtqueue interrupt with no work for %p\n", vq); 384 return IRQ_NONE; 385 } 386 387 if (unlikely(vq->broken)) 388 return IRQ_HANDLED; 389 390 pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback); 391 if (vq->vq.callback) 392 vq->vq.callback(&vq->vq); 393 394 return IRQ_HANDLED; 395 } 396 EXPORT_SYMBOL_GPL(vring_interrupt); 397 398 static struct virtqueue_ops vring_vq_ops = { 399 .add_buf = vring_add_buf, 400 .get_buf = vring_get_buf, 401 .kick = vring_kick, 402 .disable_cb = vring_disable_cb, 403 .enable_cb = vring_enable_cb, 404 .detach_unused_buf = vring_detach_unused_buf, 405 }; 406 407 struct virtqueue *vring_new_virtqueue(unsigned int num, 408 unsigned int vring_align, 409 struct virtio_device *vdev, 410 void *pages, 411 void (*notify)(struct virtqueue *), 412 void (*callback)(struct virtqueue *), 413 const char *name) 414 { 415 struct vring_virtqueue *vq; 416 unsigned int i; 417 418 /* We assume num is a power of 2. */ 419 if (num & (num - 1)) { 420 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num); 421 return NULL; 422 } 423 424 vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL); 425 if (!vq) 426 return NULL; 427 428 vring_init(&vq->vring, num, pages, vring_align); 429 vq->vq.callback = callback; 430 vq->vq.vdev = vdev; 431 vq->vq.vq_ops = &vring_vq_ops; 432 vq->vq.name = name; 433 vq->notify = notify; 434 vq->broken = false; 435 vq->last_used_idx = 0; 436 vq->num_added = 0; 437 list_add_tail(&vq->vq.list, &vdev->vqs); 438 #ifdef DEBUG 439 vq->in_use = false; 440 #endif 441 442 vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC); 443 444 /* No callback? Tell other side not to bother us. */ 445 if (!callback) 446 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT; 447 448 /* Put everything in free lists. */ 449 vq->num_free = num; 450 vq->free_head = 0; 451 for (i = 0; i < num-1; i++) { 452 vq->vring.desc[i].next = i+1; 453 vq->data[i] = NULL; 454 } 455 vq->data[i] = NULL; 456 457 return &vq->vq; 458 } 459 EXPORT_SYMBOL_GPL(vring_new_virtqueue); 460 461 void vring_del_virtqueue(struct virtqueue *vq) 462 { 463 list_del(&vq->list); 464 kfree(to_vvq(vq)); 465 } 466 EXPORT_SYMBOL_GPL(vring_del_virtqueue); 467 468 /* Manipulates transport-specific feature bits. */ 469 void vring_transport_features(struct virtio_device *vdev) 470 { 471 unsigned int i; 472 473 for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) { 474 switch (i) { 475 case VIRTIO_RING_F_INDIRECT_DESC: 476 break; 477 default: 478 /* We don't understand this bit. */ 479 clear_bit(i, vdev->features); 480 } 481 } 482 } 483 EXPORT_SYMBOL_GPL(vring_transport_features); 484 485 MODULE_LICENSE("GPL"); 486