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
  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");