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 #ifdef DEBUG
  25 /* For development, we want to crash whenever the ring is screwed. */
  26 #define BAD_RING(_vq, fmt...)                   \
  27         do { dev_err(&(_vq)->vq.vdev->dev, fmt); BUG(); } while(0)
  28 /* Caller is supposed to guarantee no reentry. */
  29 #define START_USE(_vq)                                          \
  30         do {                                                    \
  31                 if ((_vq)->in_use)                              \
  32                         panic("in_use = %i\n", (_vq)->in_use);  \
  33                 (_vq)->in_use = __LINE__;                       \
  34                 mb();                                           \
  35         } while(0)
  36 #define END_USE(_vq) \
  37         do { BUG_ON(!(_vq)->in_use); (_vq)->in_use = 0; mb(); } while(0)
  38 #else
  39 #define BAD_RING(_vq, fmt...)                   \
  40         do { dev_err(&_vq->vq.vdev->dev, fmt); (_vq)->broken = true; } while(0)
  41 #define START_USE(vq)
  42 #define END_USE(vq)
  43 #endif
  44
  45 struct vring_virtqueue
  46 {
  47         struct virtqueue vq;
  48
  49         /* Actual memory layout for this queue */
  50         struct vring vring;
  51
  52         /* Other side has made a mess, don't try any more. */
  53         bool broken;
  54
  55         /* Number of free buffers */
  56         unsigned int num_free;
  57         /* Head of free buffer list. */
  58         unsigned int free_head;
  59         /* Number we've added since last sync. */
  60         unsigned int num_added;
  61
  62         /* Last used index we've seen. */
  63         u16 last_used_idx;
  64
  65         /* How to notify other side. FIXME: commonalize hcalls! */
  66         void (*notify)(struct virtqueue *vq);
  67
  68 #ifdef DEBUG
  69         /* They're supposed to lock for us. */
  70         unsigned int in_use;
  71 #endif
  72
  73         /* Tokens for callbacks. */
  74         void *data[];
  75 };
  76
  77 #define to_vvq(_vq) container_of(_vq, struct vring_virtqueue, vq)
  78
  79 static int vring_add_buf(struct virtqueue *_vq,
  80                          struct scatterlist sg[],
  81                          unsigned int out,
  82                          unsigned int in,
  83                          void *data)
  84 {
  85         struct vring_virtqueue *vq = to_vvq(_vq);
  86         unsigned int i, avail, head, uninitialized_var(prev);
  87
  88         BUG_ON(data == NULL);
  89         BUG_ON(out + in > vq->vring.num);
  90         BUG_ON(out + in == 0);
  91
  92         START_USE(vq);
  93
  94         if (vq->num_free < out + in) {
  95                 pr_debug("Can't add buf len %i - avail = %i\n",
  96                          out + in, vq->num_free);
  97                 /* FIXME: for historical reasons, we force a notify here if
  98                  * there are outgoing parts to the buffer.  Presumably the
  99                  * host should service the ring ASAP. */
 100                 if (out)
 101                         vq->notify(&vq->vq);
 102                 END_USE(vq);
 103                 return -ENOSPC;
 104         }
 105
 106         /* We're about to use some buffers from the free list. */
 107         vq->num_free -= out + in;
 108
 109         head = vq->free_head;
 110         for (i = vq->free_head; out; i = vq->vring.desc[i].next, out--) {
 111                 vq->vring.desc[i].flags = VRING_DESC_F_NEXT;
 112                 vq->vring.desc[i].addr = sg_phys(sg);
 113                 vq->vring.desc[i].len = sg->length;
 114                 prev = i;
 115                 sg++;
 116         }
 117         for (; in; i = vq->vring.desc[i].next, in--) {
 118                 vq->vring.desc[i].flags = VRING_DESC_F_NEXT|VRING_DESC_F_WRITE;
 119                 vq->vring.desc[i].addr = sg_phys(sg);
 120                 vq->vring.desc[i].len = sg->length;
 121                 prev = i;
 122                 sg++;
 123         }
 124         /* Last one doesn't continue. */
 125         vq->vring.desc[prev].flags &= ~VRING_DESC_F_NEXT;
 126
 127         /* Update free pointer */
 128         vq->free_head = i;
 129
 130         /* Set token. */
 131         vq->data[head] = data;
 132
 133         /* Put entry in available array (but don't update avail->idx until they
 134          * do sync).  FIXME: avoid modulus here? */
 135         avail = (vq->vring.avail->idx + vq->num_added++) % vq->vring.num;
 136         vq->vring.avail->ring[avail] = head;
 137
 138         pr_debug("Added buffer head %i to %p\n", head, vq);
 139         END_USE(vq);
 140         return 0;
 141 }
 142
 143 static void vring_kick(struct virtqueue *_vq)
 144 {
 145         struct vring_virtqueue *vq = to_vvq(_vq);
 146         START_USE(vq);
 147         /* Descriptors and available array need to be set before we expose the
 148          * new available array entries. */
 149         wmb();
 150
 151         vq->vring.avail->idx += vq->num_added;
 152         vq->num_added = 0;
 153
 154         /* Need to update avail index before checking if we should notify */
 155         mb();
 156
 157         if (!(vq->vring.used->flags & VRING_USED_F_NO_NOTIFY))
 158                 /* Prod other side to tell it about changes. */
 159                 vq->notify(&vq->vq);
 160
 161         END_USE(vq);
 162 }
 163
 164 static void detach_buf(struct vring_virtqueue *vq, unsigned int head)
 165 {
 166         unsigned int i;
 167
 168         /* Clear data ptr. */
 169         vq->data[head] = NULL;
 170
 171         /* Put back on free list: find end */
 172         i = head;
 173         while (vq->vring.desc[i].flags & VRING_DESC_F_NEXT) {
 174                 i = vq->vring.desc[i].next;
 175                 vq->num_free++;
 176         }
 177
 178         vq->vring.desc[i].next = vq->free_head;
 179         vq->free_head = head;
 180         /* Plus final descriptor */
 181         vq->num_free++;
 182 }
 183
 184 static inline bool more_used(const struct vring_virtqueue *vq)
 185 {
 186         return vq->last_used_idx != vq->vring.used->idx;
 187 }
 188
 189 static void *vring_get_buf(struct virtqueue *_vq, unsigned int *len)
 190 {
 191         struct vring_virtqueue *vq = to_vvq(_vq);
 192         void *ret;
 193         unsigned int i;
 194
 195         START_USE(vq);
 196
 197         if (unlikely(vq->broken)) {
 198                 END_USE(vq);
 199                 return NULL;
 200         }
 201
 202         if (!more_used(vq)) {
 203                 pr_debug("No more buffers in queue\n");
 204                 END_USE(vq);
 205                 return NULL;
 206         }
 207
 208         i = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].id;
 209         *len = vq->vring.used->ring[vq->last_used_idx%vq->vring.num].len;
 210
 211         if (unlikely(i >= vq->vring.num)) {
 212                 BAD_RING(vq, "id %u out of range\n", i);
 213                 return NULL;
 214         }
 215         if (unlikely(!vq->data[i])) {
 216                 BAD_RING(vq, "id %u is not a head!\n", i);
 217                 return NULL;
 218         }
 219
 220         /* detach_buf clears data, so grab it now. */
 221         ret = vq->data[i];
 222         detach_buf(vq, i);
 223         vq->last_used_idx++;
 224         END_USE(vq);
 225         return ret;
 226 }
 227
 228 static void vring_disable_cb(struct virtqueue *_vq)
 229 {
 230         struct vring_virtqueue *vq = to_vvq(_vq);
 231
 232         vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 233 }
 234
 235 static bool vring_enable_cb(struct virtqueue *_vq)
 236 {
 237         struct vring_virtqueue *vq = to_vvq(_vq);
 238
 239         START_USE(vq);
 240
 241         /* We optimistically turn back on interrupts, then check if there was
 242          * more to do. */
 243         vq->vring.avail->flags &= ~VRING_AVAIL_F_NO_INTERRUPT;
 244         mb();
 245         if (unlikely(more_used(vq))) {
 246                 END_USE(vq);
 247                 return false;
 248         }
 249
 250         END_USE(vq);
 251         return true;
 252 }
 253
 254 irqreturn_t vring_interrupt(int irq, void *_vq)
 255 {
 256         struct vring_virtqueue *vq = to_vvq(_vq);
 257
 258         if (!more_used(vq)) {
 259                 pr_debug("virtqueue interrupt with no work for %p\n", vq);
 260                 return IRQ_NONE;
 261         }
 262
 263         if (unlikely(vq->broken))
 264                 return IRQ_HANDLED;
 265
 266         pr_debug("virtqueue callback for %p (%p)\n", vq, vq->vq.callback);
 267         if (vq->vq.callback)
 268                 vq->vq.callback(&vq->vq);
 269
 270         return IRQ_HANDLED;
 271 }
 272 EXPORT_SYMBOL_GPL(vring_interrupt);
 273
 274 static struct virtqueue_ops vring_vq_ops = {
 275         .add_buf = vring_add_buf,
 276         .get_buf = vring_get_buf,
 277         .kick = vring_kick,
 278         .disable_cb = vring_disable_cb,
 279         .enable_cb = vring_enable_cb,
 280 };
 281
 282 struct virtqueue *vring_new_virtqueue(unsigned int num,
 283                                       unsigned int vring_align,
 284                                       struct virtio_device *vdev,
 285                                       void *pages,
 286                                       void (*notify)(struct virtqueue *),
 287                                       void (*callback)(struct virtqueue *))
 288 {
 289         struct vring_virtqueue *vq;
 290         unsigned int i;
 291
 292         /* We assume num is a power of 2. */
 293         if (num & (num - 1)) {
 294                 dev_warn(&vdev->dev, "Bad virtqueue length %u\n", num);
 295                 return NULL;
 296         }
 297
 298         vq = kmalloc(sizeof(*vq) + sizeof(void *)*num, GFP_KERNEL);
 299         if (!vq)
 300                 return NULL;
 301
 302         vring_init(&vq->vring, num, pages, vring_align);
 303         vq->vq.callback = callback;
 304         vq->vq.vdev = vdev;
 305         vq->vq.vq_ops = &vring_vq_ops;
 306         vq->notify = notify;
 307         vq->broken = false;
 308         vq->last_used_idx = 0;
 309         vq->num_added = 0;
 310 #ifdef DEBUG
 311         vq->in_use = false;
 312 #endif
 313
 314         /* No callback?  Tell other side not to bother us. */
 315         if (!callback)
 316                 vq->vring.avail->flags |= VRING_AVAIL_F_NO_INTERRUPT;
 317
 318         /* Put everything in free lists. */
 319         vq->num_free = num;
 320         vq->free_head = 0;
 321         for (i = 0; i < num-1; i++)
 322                 vq->vring.desc[i].next = i+1;
 323
 324         return &vq->vq;
 325 }
 326 EXPORT_SYMBOL_GPL(vring_new_virtqueue);
 327
 328 void vring_del_virtqueue(struct virtqueue *vq)
 329 {
 330         kfree(to_vvq(vq));
 331 }
 332 EXPORT_SYMBOL_GPL(vring_del_virtqueue);
 333
 334 /* Manipulates transport-specific feature bits. */
 335 void vring_transport_features(struct virtio_device *vdev)
 336 {
 337         unsigned int i;
 338
 339         for (i = VIRTIO_TRANSPORT_F_START; i < VIRTIO_TRANSPORT_F_END; i++) {
 340                 switch (i) {
 341                 default:
 342                         /* We don't understand this bit. */
 343                         clear_bit(i, vdev->features);
 344                 }
 345         }
 346 }
 347 EXPORT_SYMBOL_GPL(vring_transport_features);
 348
 349 MODULE_LICENSE("GPL");