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 #include <linux/module.h>
  25
  26 /* virtio guest is communicating with a virtual "device" that actually runs on
  27  * a host processor.  Memory barriers are used to control SMP effects. */
  28 #ifdef CONFIG_SMP
  29 /* Where possible, use SMP barriers which are more lightweight than mandatory
  30  * barriers, because mandatory barriers control MMIO effects on accesses
  31  * through relaxed memory I/O windows (which virtio does not use). */
  32 #define virtio_mb() smp_mb()
  33 #define virtio_rmb() smp_rmb()
  34 #define virtio_wmb() smp_wmb()
  35 #else
  36 /* We must force memory ordering even if guest is UP since host could be
  37  * running on another CPU, but SMP barriers are defined to barrier() in that
  38  * configuration. So fall back to mandatory barriers instead. */
  39 #define virtio_mb() mb()
  40 #define virtio_rmb() rmb()
  41 #define virtio_wmb() wmb()
  42 #endif
  43
  44 #ifdef DEBUG
  45 /* For development, we want to crash whenever the ring is screwed. */
  46 #define BAD_RING(_vq, fmt, args...)                             \
  47         do {                                                    \
  48                 dev_err(&(_vq)->vq.vdev->dev,                   \
  49                         "%s:"fmt, (_vq)->vq.name, ##args);      \
  50                 BUG();                                          \
  51         } while (0)
  52 /* Caller is supposed to guarantee no reentry. */
  53 #define START_USE(_vq)                                          \
  54         do {                                                    \
  55                 if ((_vq)->in_use)                              \
  56                         panic("%s:in_use = %i\n",               \
  57                               (_vq)->vq.name, (_vq)->in_use);   \
  58                 (_vq)->in_use = __LINE__;                       \
  59         } while (0)
  60 #define END_USE(_vq) \
  61         do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; } while(0)
  62 #else
  63 #define BAD_RING(_vq, fmt, args...)                             \
  64         do {                                                    \
  65                 dev_err(&_vq->vq.vdev->dev,                     \
  66                         "%s:"fmt, (_vq)->vq.name, ##args);      \
  67                 (_vq)->broken = true;                           \
  68         } while (0)
  69 #define START_USE(vq)
  70 #define END_USE(vq)
  71 #endif
  72
  73 struct vring_virtqueue
  74 {
  75         struct virtqueue vq;
  76
  77         /* Actual memory layout for this queue */
  78         struct vring vring;
  79
  80         /* Other side has made a mess, don't try any more. */
  81         bool broken;
  82
  83         /* Host supports indirect buffers */
  84         bool indirect;
  85
  86         /* Host publishes avail event idx */
  87         bool event;
  88
  89         /* Number of free buffers */
  90         unsigned int num_free;
  91         /* Head of free buffer list. */
  92         unsigned int free_head;
  93         /* Number we've added since last sync. */
  94         unsigned int num_added;
  95
  96         /* Last used index we've seen. */
  97         u16 last_used_idx;
  98
  99         /* How to notify other side. FIXME: commonalize hcalls! */
 100         void (*notify)(struct virtqueue *vq);
 101
 102 #ifdef DEBUG
 103         /* They're supposed to lock for us. */
 104         unsigned int in_use;
 105 #endif
 106
 107         /* Tokens for callbacks. */
 108         void *data[];
 109 };
 110
 111 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
 112
 113 /* Set up an indirect table of descriptors and add it to the queue. */
 114 static int vring_add_indirect(struct vring_virtqueue *vq,
 115                               struct scatterlist sg[],
 116                               unsigned int out,
 117                               unsigned int in,
 118                               gfp_t gfp)
 119 {
 120         struct vring_desc *desc;
 121         unsigned head;
 122         int i;
 123
 124         desc = kmalloc((out + in) * sizeof(struct vring_desc), gfp);
 125         if (!desc)
 126                 return -ENOMEM;
 127
 128         /* Transfer entries from the sg list into the indirect page */
 129         for (i = 0; i < out; i++) {
 130                 desc[i].flags = VRING_DESC_F_NEXT;
 131                 desc[i].addr = sg_phys(sg);
 132                 desc[i].len = sg->length;
 133                 desc[i].next = i+1;
 134                 sg++;
 135         }
 136         for (; i < (out + in); i++) {
 137                 desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 138                 desc[i].addr = sg_phys(sg);
 139                 desc[i].len = sg->length;
 140                 desc[i].next = i+1;
 141                 sg++;
 142         }
 143
 144         /* Last one doesn't continue. */
 145         desc[i-1].flags &= ~VRING_DESC_F_NEXT;
 146         desc[i-1].next = 0;
 147
 148         /* We're about to use a buffer */
 149         vq->num_free--;
 150
 151         /* Use a single buffer which doesn't continue */
 152         head = vq->free_head;
 153         vq->vring.desc[head].flags = VRING_DESC_F_INDIRECT;
 154         vq->vring.desc[head].addr = virt_to_phys(desc);
 155         vq->vring.desc[head].len = i * sizeof(struct vring_desc);
 156
 157         /* Update free pointer */
 158         vq->free_head = vq->vring.desc[head].next;
 159
 160         return head;
 161 }
 162
 163 int virtqueue_add_buf_gfp(struct virtqueue *_vq,
 164                           struct scatterlist sg[],
 165                           unsigned int out,
 166                           unsigned int in,
 167                           void *data,
 168                           gfp_t gfp)
 169 {
 170         struct vring_virtqueue *vq = to_vvq(_vq);
 171         unsigned int i, avail, uninitialized_var(prev);
 172         int head;
 173
 174         START_USE(vq);
 175
 176         BUG_ON(data == NULL);
 177
 178         /* If the host supports indirect descriptor tables, and we have multiple
 179          * buffers, then go indirect. FIXME: tune this threshold */
 180         if (vq->indirect && (out + in) > 1 && vq->num_free) {
 181                 head = vring_add_indirect(vq, sg, out, in, gfp);
 182                 if (likely(head >= 0))
 183                         goto add_head;
 184         }
 185
 186         BUG_ON(out + in > vq->vring.num);
 187         BUG_ON(out + in == 0);
 188
 189         if (vq->num_free < out + in) {
 190                 pr_debug("Can't add buf len %i - avail = %i\n",
 191                          out + in, vq->num_free);
 192                 /* FIXME: for historical reasons, we force a notify here if
 193                  * there are outgoing parts to the buffer.  Presumably the
 194                  * host should service the ring ASAP. */
 195                 if (out)
 196                         vq->notify(&vq->vq);
 197                 END_USE(vq);
 198                 return -ENOSPC;
 199         }
 200
 201         /* We're about to use some buffers from the free list. */
 202         vq->num_free -= out + in;
 203
 204         head = vq->free_head;
 205         for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
 206                 vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
 207                 vq->vring.desc[i].addr = sg_phys(sg);
 208                 vq->vring.desc[i].len = sg->length;
 209                 prev = i;
 210                 sg++;
 211         }
 212         for (; in; i = vq->vring.desc[i].next, in--) {
 213                 vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 214                 vq->vring.desc[i].addr = sg_phys(sg);
 215                 vq->vring.desc[i].len = sg->length;
 216                 prev = i;
 217                 sg++;
 218         }
 219         /* Last one doesn't continue. */
 220         vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
 221
 222         /* Update free pointer */
 223         vq->free_head = i;
 224
 225 add_head:
 226         /* Set token. */
 227         vq->data[head] = data;
 228
 229         /* Put entry in available array (but don't update avail->idx until they
 230          * do sync).  FIXME: avoid modulus here? */
 231         avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
 232         vq->vring.avail->ring[avail] = head;
 233
 234         pr_debug("Added buffer head %i to %p\n", head, vq);
 235         END_USE(vq);
 236
 237         return vq->num_free;
 238 }
 239 EXPORT_SYMBOL_GPL(virtqueue_add_buf_gfp);
 240
 241 void virtqueue_kick(struct virtqueue *_vq)
 242 {
 243         struct vring_virtqueue *vq = to_vvq(_vq);
 244         u16 new, old;
 245         START_USE(vq);
 246         /* Descriptors and available array need to be set before we expose the
 247          * new available array entries. */
 248         virtio_wmb();
 249
 250         old = vq->vring.avail->idx;
 251         new = vq->vring.avail->idx = old + vq->num_added;
 252         vq->num_added = 0;
 253
 254         /* Need to update avail index before checking if we should notify */
 255         virtio_mb();
 256
 257         if (vq->event ?
 258             vring_need_event(vring_avail_event(&vq->vring), new, old) :
 259             !(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
 260                 /* Prod other side to tell it about changes. */
 261                 vq->notify(&vq->vq);
 262
 263         END_USE(vq);
 264 }
 265 EXPORT_SYMBOL_GPL(virtqueue_kick);
 266
 267 static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
 268 {
 269         unsigned int i;
 270
 271         /* Clear data ptr. */
 272         vq->data[head] = NULL;
 273
 274         /* Put back on free list: find end */
 275         i = head;
 276
 277         /* Free the indirect table */
 278         if (vq->vring.desc[i].flags & VRING_DESC_F_INDIRECT)
 279                 kfree(phys_to_virt(vq->vring.desc[i].addr));
 280
 281         while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
 282                 i = vq->vring.desc[i].next;
 283                 vq->num_free++;
 284         }
 285
 286         vq->vring.desc[i].next = vq->free_head;
 287         vq->free_head = head;
 288         /* Plus final descriptor */
 289         vq->num_free++;
 290 }
 291
 292 static inline bool more_used(const struct vring_virtqueue *vq)
 293 {
 294         return vq->last_used_idx != vq->vring.used->idx;
 295 }
 296
 297 void *virtqueue_get_buf(struct virtqueue *_vq, unsigned int *len)
 298 {
 299         struct vring_virtqueue *vq = to_vvq(_vq);
 300         void *ret;
 301         unsigned int i;
 302
 303         START_USE(vq);
 304
 305         if (unlikely(vq->broken)) {
 306                 END_USE(vq);
 307                 return NULL;
 308         }
 309
 310         if (!more_used(vq)) {
 311                 pr_debug("No more buffers in queue\n");
 312                 END_USE(vq);
 313                 return NULL;
 314         }
 315
 316         /* Only get used array entries after they have been exposed by host. */
 317         virtio_rmb();
 318
 319         i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
 320         *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
 321
 322         if (unlikely(i >= vq->vring.num)) {
 323                 BAD_RING(vq, "id %u out of range\n", i);
 324                 return NULL;
 325         }
 326         if (unlikely(!vq->data[i])) {
 327                 BAD_RING(vq, "id %u is not a head!\n", i);
 328                 return NULL;
 329         }
 330
 331         /* detach_buf clears data, so grab it now. */
 332         ret = vq->data[i];
 333         detach_buf(vq, i);
 334         vq->last_used_idx++;
 335         /* If we expect an interrupt for the next entry, tell host
 336          * by writing event index and flush out the write before
 337          * the read in the next get_buf call. */
 338         if (!(vq->vring.avail->flags & VRING_AVAIL_F_NO_INTERRUPT)) {
 339                 vring_used_event(&vq->vring) = vq->last_used_idx;
 340                 virtio_mb();
 341         }
 342
 343         END_USE(vq);
 344         return ret;
 345 }
 346 EXPORT_SYMBOL_GPL(virtqueue_get_buf);
 347
 348 void virtqueue_disable_cb(struct virtqueue *_vq)
 349 {
 350         struct vring_virtqueue *vq = to_vvq(_vq);
 351
 352         vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 353 }
 354 EXPORT_SYMBOL_GPL(virtqueue_disable_cb);
 355
 356 bool virtqueue_enable_cb(struct virtqueue *_vq)
 357 {
 358         struct vring_virtqueue *vq = to_vvq(_vq);
 359
 360         START_USE(vq);
 361
 362         /* We optimistically turn back on interrupts, then check if there was
 363          * more to do. */
 364         /* Depending on the VIRTIO_RING_F_EVENT_IDX feature, we need to
 365          * either clear the flags bit or point the event index at the next
 366          * entry. Always do both to keep code simple. */
 367         vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
 368         vring_used_event(&vq->vring) = vq->last_used_idx;
 369         virtio_mb();
 370         if (unlikely(more_used(vq))) {
 371                 END_USE(vq);
 372                 return false;
 373         }
 374
 375         END_USE(vq);
 376         return true;
 377 }
 378 EXPORT_SYMBOL_GPL(virtqueue_enable_cb);
 379
 380 bool virtqueue_enable_cb_delayed(struct virtqueue *_vq)
 381 {
 382         struct vring_virtqueue *vq = to_vvq(_vq);
 383         u16 bufs;
 384
 385         START_USE(vq);
 386
 387         /* We optimistically turn back on interrupts, then check if there was
 388          * more to do. */
 389         /* Depending on the VIRTIO_RING_F_USED_EVENT_IDX feature, we need to
 390          * either clear the flags bit or point the event index at the next
 391          * entry. Always do both to keep code simple. */
 392         vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
 393         /* TODO: tune this threshold */
 394         bufs = (u16)(vq->vring.avail->idx - vq->last_used_idx) * 3 / 4;
 395         vring_used_event(&vq->vring) = vq->last_used_idx + bufs;
 396         virtio_mb();
 397         if (unlikely((u16)(vq->vring.used->idx - vq->last_used_idx) > bufs)) {
 398                 END_USE(vq);
 399                 return false;
 400         }
 401
 402         END_USE(vq);
 403         return true;
 404 }
 405 EXPORT_SYMBOL_GPL(virtqueue_enable_cb_delayed);
 406
 407 void *virtqueue_detach_unused_buf(struct virtqueue *_vq)
 408 {
 409         struct vring_virtqueue *vq = to_vvq(_vq);
 410         unsigned int i;
 411         void *buf;
 412
 413         START_USE(vq);
 414
 415         for (i = 0; i < vq->vring.num; i++) {
 416                 if (!vq->data[i])
 417                         continue;
 418                 /* detach_buf clears data, so grab it now. */
 419                 buf = vq->data[i];
 420                 detach_buf(vq, i);
 421                 vq->vring.avail->idx--;
 422                 END_USE(vq);
 423                 return buf;
 424         }
 425         /* That should have freed everything. */
 426         BUG_ON(vq->num_free != vq->vring.num);
 427
 428         END_USE(vq);
 429         return NULL;
 430 }
 431 EXPORT_SYMBOL_GPL(virtqueue_detach_unused_buf);
 432
 433 irqreturn_t vring_interrupt(int irq, void *_vq)
 434 {
 435         struct vring_virtqueue *vq = to_vvq(_vq);
 436
 437         if (!more_used(vq)) {
 438                 pr_debug("virtqueue interrupt with no work for %p\n", vq);
 439                 return IRQ_NONE;
 440         }
 441
 442         if (unlikely(vq->broken))
 443                 return IRQ_HANDLED;
 444
 445         pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
 446         if (vq->vq.callback)
 447                 vq->vq.callback(&vq->vq);
 448
 449         return IRQ_HANDLED;
 450 }
 451 EXPORT_SYMBOL_GPL(vring_interrupt);
 452
 453 struct virtqueue *vring_new_virtqueue(unsigned int num,
 454                                       unsigned int vring_align,
 455                                       struct virtio_device *vdev,
 456                                       void *pages,
 457                                       void (*notify)(struct virtqueue *),
 458                                       void (*callback)(struct virtqueue *),
 459                                       const char *name)
 460 {
 461         struct vring_virtqueue *vq;
 462         unsigned int i;
 463
 464         /* We assume num is a power of 2. */
 465         if (num & (num - 1)) {
 466                 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
 467                 return NULL;
 468         }
 469
 470         vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
 471         if (!vq)
 472                 return NULL;
 473
 474         vring_init(&vq->vring, num, pages, vring_align);
 475         vq->vq.callback = callback;
 476         vq->vq.vdev = vdev;
 477         vq->vq.name = name;
 478         vq->notify = notify;
 479         vq->broken = false;
 480         vq->last_used_idx = 0;
 481         vq->num_added = 0;
 482         list_add_tail(&vq->vq.list, &vdev->vqs);
 483 #ifdef DEBUG
 484         vq->in_use = false;
 485 #endif
 486
 487         vq->indirect = virtio_has_feature(vdev, VIRTIO_RING_F_INDIRECT_DESC);
 488         vq->event = virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX);
 489
 490         /* No callback?  Tell other side not to bother us. */
 491         if (!callback)
 492                 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 493
 494         /* Put everything in free lists. */
 495         vq->num_free = num;
 496         vq->free_head = 0;
 497         for (i = 0; i < num-1; i++) {
 498                 vq->vring.desc[i].next = i+1;
 499                 vq->data[i] = NULL;
 500         }
 501         vq->data[i] = NULL;
 502
 503         return &vq->vq;
 504 }
 505 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
 506
 507 void vring_del_virtqueue(struct virtqueue *vq)
 508 {
 509         list_del(&vq->list);
 510         kfree(to_vvq(vq));
 511 }
 512 EXPORT_SYMBOL_GPL(vring_del_virtqueue);
 513
 514 /* Manipulates transport-specific feature bits. */
 515 void vring_transport_features(struct virtio_device *vdev)
 516 {
 517         unsigned int i;
 518
 519         for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
 520                 switch (i) {
 521                 case VIRTIO_RING_F_INDIRECT_DESC:
 522                         break;
 523                 case VIRTIO_RING_F_EVENT_IDX:
 524                         break;
 525                 default:
 526                         /* We don't understand this bit. */
 527                         clear_bit(i, vdev->features);
 528                 }
 529         }
 530 }
 531 EXPORT_SYMBOL_GPL(vring_transport_features);
 532
 533 MODULE_LICENSE("GPL");