drivers/virtio/virtio_ring.c

   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         /* Host publishes avail event idx */
  86         bool event;
  87
  88         /* Number of free buffers */
  89         unsigned int num_free;
  90         /* Head of free buffer list. */
  91         unsigned int free_head;
  92         /* Number we've added since last sync. */
  93         unsigned int num_added;
  94
  95         /* Last used index we've seen. */
  96         u16 last_used_idx;
  97
  98         /* How to notify other side. FIXME: commonalize hcalls! */
  99         void (*notify)(struct virtqueue *vq);
 100
 101 #ifdef DEBUG
 102         /* They're supposed to lock for us. */
 103         unsigned int in_use;
 104 #endif
 105
 106         /* Tokens for callbacks. */
 107         void *data[];
 108 };
 109
 110 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
 111
 112 /* Set up an indirect table of descriptors and add it to the queue. */
 113 static int vring_add_indirect(struct vring_virtqueue *vq,
 114                               struct scatterlist sg[],
 115                               unsigned int out,
 116                               unsigned int in,
 117                               gfp_t gfp)
 118 {
 119         struct vring_desc *desc;
 120         unsigned head;
 121         int i;
 122
 123         desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
 124         if (!desc)
 125                 return -ENOMEM;
 126
 127         /* Transfer entries from the sg list into the indirect page */
 128         for (i = 0; i < out; i++) {
 129                 desc[i].flags = VRING_DESC_F_NEXT;
 130                 desc[i].addr = sg_phys(sg);
 131                 desc[i].len = sg->length;
 132                 desc[i].next = i+1;
 133                 sg++;
 134         }
 135         for (; i < (out + in); i++) {
 136                 desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 137                 desc[i].addr = sg_phys(sg);
 138                 desc[i].len = sg->length;
 139                 desc[i].next = i+1;
 140                 sg++;
 141         }
 142
 143         /* Last one doesn't continue. */
 144         desc[i-1].flags &= ~VRING_DESC_F_NEXT;
 145         desc[i-1].next = 0;
 146
 147         /* We're about to use a buffer */
 148         vq->num_free--;
 149
 150         /* Use a single buffer which doesn't continue */
 151         head = vq->free_head;
 152         vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
 153         vq->vring.desc[head].addr = virt_to_phys(desc);
 154         vq->vring.desc[head].len = i * sizeof(struct vring_desc);
 155
 156         /* Update free pointer */
 157         vq->free_head = vq->vring.desc[head].next;
 158
 159         return head;
 160 }
 161
 162 int virtqueue_add_buf_gfp(struct virtqueue *_vq,
 163                           struct scatterlist sg[],
 164                           unsigned int out,
 165                           unsigned int in,
 166                           void *data,
 167                           gfp_t gfp)
 168 {
 169         struct vring_virtqueue *vq = to_vvq(_vq);
 170         unsigned int i, avail, uninitialized_var(prev);
 171         int head;
 172
 173         START_USE(vq);
 174
 175         BUG_ON(data == NULL);
 176
 177         /* If the host supports indirect descriptor tables, and we have multiple
 178          * buffers, then go indirect. FIXME: tune this threshold */
 179         if (vq->indirect && (out + in) > 1 && vq->num_free) {
 180                 head = vring_add_indirect(vq, sg, out, in, gfp);
 181                 if (likely(head >= 0))
 182                         goto add_head;
 183         }
 184
 185         BUG_ON(out + in > vq->vring.num);
 186         BUG_ON(out + in == 0);
 187
 188         if (vq->num_free < out + in) {
 189                 pr_debug("Can't add buf len %i - avail = %i\n",
 190                          out + in, vq->num_free);
 191                 /* FIXME: for historical reasons, we force a notify here if
 192                  * there are outgoing parts to the buffer.  Presumably the
 193                  * host should service the ring ASAP. */
 194                 if (out)
 195                         vq->notify(&vq->vq);
 196                 END_USE(vq);
 197                 return -ENOSPC;
 198         }
 199
 200         /* We're about to use some buffers from the free list. */
 201         vq->num_free -= out + in;
 202
 203         head = vq->free_head;
 204         for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
 205                 vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
 206                 vq->vring.desc[i].addr = sg_phys(sg);
 207                 vq->vring.desc[i].len = sg->length;
 208                 prev = i;
 209                 sg++;
 210         }
 211         for (; in; i = vq->vring.desc[i].next, in--) {
 212                 vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 213                 vq->vring.desc[i].addr = sg_phys(sg);
 214                 vq->vring.desc[i].len = sg->length;
 215                 prev = i;
 216                 sg++;
 217         }
 218         /* Last one doesn't continue. */
 219         vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
 220
 221         /* Update free pointer */
 222         vq->free_head = i;
 223
 224 add_head:
 225         /* Set token. */
 226         vq->data[head] = data;
 227
 228         /* Put entry in available array (but don't update avail->idx until they
 229          * do sync).  FIXME: avoid modulus here? */
 230         avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
 231         vq->vring.avail->ring[avail] = head;
 232
 233         pr_debug("Added buffer head %i to %p\n", head, vq);
 234         END_USE(vq);
 235
 236         return vq->num_free;
 237 }
 238 EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);
 239
 240 void virtqueue_kick(struct virtqueue *_vq)
 241 {
 242         struct vring_virtqueue *vq = to_vvq(_vq);
 243         u16 new, old;
 244         START_USE(vq);
 245         /* Descriptors and available array need to be set before we expose the
 246          * new available array entries. */
 247         virtio_wmb();
 248
 249         old = vq->vring.avail->idx;
 250         new = vq->vring.avail->idx = old + vq->num_added;
 251         vq->num_added = 0;
 252
 253         /* Need to update avail index before checking if we should notify */
 254         virtio_mb();
 255
 256         if (vq->event ?
 257             vring_need_event(vring_avail_event(&vq->vring), new, old) :
 258             !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
 259                 /* Prod other side to tell it about changes. */
 260                 vq->notify(&vq->vq);
 261
 262         END_USE(vq);
 263 }
 264 EXPORT_SYMBOL_GPL(virtqueue_kick);
 265
 266 static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
 267 {
 268         unsigned int i;
 269
 270         /* Clear data ptr. */
 271         vq->data[head] = NULL;
 272
 273         /* Put back on free list: find end */
 274         i = head;
 275
 276         /* Free the indirect table */
 277         if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
 278                 kfree(phys_to_virt(vq->vring.desc[i].addr));
 279
 280         while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
 281                 i = vq->vring.desc[i].next;
 282                 vq->num_free++;
 283         }
 284
 285         vq->vring.desc[i].next = vq->free_head;
 286         vq->free_head = head;
 287         /* Plus final descriptor */
 288         vq->num_free++;
 289 }
 290
 291 static inline bool more_used(const struct vring_virtqueue *vq)
 292 {
 293         return vq->last_used_idx != vq->vring.used->idx;
 294 }
 295
 296 void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
 297 {
 298         struct vring_virtqueue *vq = to_vvq(_vq);
 299         void *ret;
 300         unsigned int i;
 301
 302         START_USE(vq);
 303
 304         if (unlikely(vq->broken)) {
 305                 END_USE(vq);
 306                 return NULL;
 307         }
 308
 309         if (!more_used(vq)) {
 310                 pr_debug("No more buffers in queue\n");
 311                 END_USE(vq);
 312                 return NULL;
 313         }
 314
 315         /* Only get used array entries after they have been exposed by host. */
 316         virtio_rmb();
 317
 318         i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
 319         *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
 320
 321         if (unlikely(i >= vq->vring.num)) {
 322                 BAD_RING(vq, "id %u out of range\n", i);
 323                 return NULL;
 324         }
 325         if (unlikely(!vq->data[i])) {
 326                 BAD_RING(vq, "id %u is not a head!\n", i);
 327                 return NULL;
 328         }
 329
 330         /* detach_buf clears data, so grab it now. */
 331         ret = vq->data[i];
 332         detach_buf(vq, i);
 333         vq->last_used_idx++;
 334         /* If we expect an interrupt for the next entry, tell host
 335          * by writing event index and flush out the write before
 336          * the read in the next get_buf call. */
 337         if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) {
 338                 vring_used_event(&vq->vring) = vq->last_used_idx;
 339                 virtio_mb();
 340         }
 341
 342         END_USE(vq);
 343         return ret;
 344 }
 345 EXPORT_SYMBOL_GPL(virtqueue_get_buf);
 346
 347 void virtqueue_disable_cb(struct virtqueue *_vq)
 348 {
 349         struct vring_virtqueue *vq = to_vvq(_vq);
 350
 351         vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 352 }
 353 EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
 354
 355 bool virtqueue_enable_cb(struct virtqueue *_vq)
 356 {
 357         struct vring_virtqueue *vq = to_vvq(_vq);
 358
 359         START_USE(vq);
 360
 361         /* We optimistically turn back on interrupts, then check if there was
 362          * more to do. */
 363         /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
 364          * either clear the flags bit or point the event index at the next
 365          * entry. Always do both to keep code simple. */
 366         vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
 367         vring_used_event(&vq->vring) = vq->last_used_idx;
 368         virtio_mb();
 369         if (unlikely(more_used(vq))) {
 370                 END_USE(vq);
 371                 return false;
 372         }
 373
 374         END_USE(vq);
 375         return true;
 376 }
 377 EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
 378
 379 bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
 380 {
 381         struct vring_virtqueue *vq = to_vvq(_vq);
 382         u16 bufs;
 383
 384         START_USE(vq);
 385
 386         /* We optimistically turn back on interrupts, then check if there was
 387          * more to do. */
 388         /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
 389          * either clear the flags bit or point the event index at the next
 390          * entry. Always do both to keep code simple. */
 391         vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
 392         /* TODO: tune this threshold */
 393         bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
 394         vring_used_event(&vq->vring) = vq->last_used_idx + bufs;
 395         virtio_mb();
 396         if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) {
 397                 END_USE(vq);
 398                 return false;
 399         }
 400
 401         END_USE(vq);
 402         return true;
 403 }
 404 EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
 405
 406 void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
 407 {
 408         struct vring_virtqueue *vq = to_vvq(_vq);
 409         unsigned int i;
 410         void *buf;
 411
 412         START_USE(vq);
 413
 414         for (i = 0; i < vq->vring.num; i++) {
 415                 if (!vq->data[i])
 416                         continue;
 417                 /* detach_buf clears data, so grab it now. */
 418                 buf = vq->data[i];
 419                 detach_buf(vq, i);
 420                 vq->vring.avail->idx--;
 421                 END_USE(vq);
 422                 return buf;
 423         }
 424         /* That should have freed everything. */
 425         BUG_ON(vq->num_free != vq->vring.num);
 426
 427         END_USE(vq);
 428         return NULL;
 429 }
 430 EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
 431
 432 irqreturn_t vring_interrupt(int irq, void *_vq)
 433 {
 434         struct vring_virtqueue *vq = to_vvq(_vq);
 435
 436         if (!more_used(vq)) {
 437                 pr_debug("virtqueue interrupt with no work for %p\n", vq);
 438                 return IRQ_NONE;
 439         }
 440
 441         if (unlikely(vq->broken))
 442                 return IRQ_HANDLED;
 443
 444         pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
 445         if (vq->vq.callback)
 446                 vq->vq.callback(&vq->vq);
 447
 448         return IRQ_HANDLED;
 449 }
 450 EXPORT_SYMBOL_GPL(vring_interrupt);
 451
 452 struct virtqueue *vring_new_virtqueue(unsigned int num,
 453                                       unsigned int vring_align,
 454                                       struct virtio_device *vdev,
 455                                       void *pages,
 456                                       void (*notify)(struct virtqueue *),
 457                                       void (*callback)(struct virtqueue *),
 458                                       const char *name)
 459 {
 460         struct vring_virtqueue *vq;
 461         unsigned int i;
 462
 463         /* We assume num is a power of 2. */
 464         if (num & (num - 1)) {
 465                 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
 466                 return NULL;
 467         }
 468
 469         vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
 470         if (!vq)
 471                 return NULL;
 472
 473         vring_init(&vq->vring, num, pages, vring_align);
 474         vq->vq.callback = callback;
 475         vq->vq.vdev = vdev;
 476         vq->vq.name = name;
 477         vq->notify = notify;
 478         vq->broken = false;
 479         vq->last_used_idx = 0;
 480         vq->num_added = 0;
 481         list_add_tail(&vq->vq.list, &vdev->vqs);
 482 #ifdef DEBUG
 483         vq->in_use = false;
 484 #endif
 485
 486         vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
 487         vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
 488
 489         /* No callback?  Tell other side not to bother us. */
 490         if (!callback)
 491                 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 492
 493         /* Put everything in free lists. */
 494         vq->num_free = num;
 495         vq->free_head = 0;
 496         for (i = 0; i < num-1; i++) {
 497                 vq->vring.desc[i].next = i+1;
 498                 vq->data[i] = NULL;
 499         }
 500         vq->data[i] = NULL;
 501
 502         return &vq->vq;
 503 }
 504 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
 505
 506 void vring_del_virtqueue(struct virtqueue *vq)
 507 {
 508         list_del(&vq->list);
 509         kfree(to_vvq(vq));
 510 }
 511 EXPORT_SYMBOL_GPL(vring_del_virtqueue);
 512
 513 /* Manipulates transport-specific feature bits. */
 514 void vring_transport_features(struct virtio_device *vdev)
 515 {
 516         unsigned int i;
 517
 518         for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
 519                 switch (i) {
 520                 case VIRTIO_RING_F_INDIRECT_DESC:
 521                         break;
 522                 case VIRTIO_RING_F_EVENT_IDX:
 523                         break;
 524                 default:
 525                         /* We don't understand this bit. */
 526                         clear_bit(i, vdev->features);
 527                 }
 528         }
 529 }
 530 EXPORT_SYMBOL_GPL(vring_transport_features);
 531
 532 MODULE_LICENSE("GPL");