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