hw/virtio/dataplane/vring.c

   1 /* Copyright 2012 Red Hat, Inc.
   2  * Copyright IBM, Corp. 2012
   3  *
   4  * Based on Linux 2.6.39 vhost code:
   5  * Copyright (C) 2009 Red Hat, Inc.
   6  * Copyright (C) 2006 Rusty Russell IBM Corporation
   7  *
   8  * Author: Michael S. Tsirkin <mst@redhat.com>
   9  *         Stefan Hajnoczi <stefanha@redhat.com>
  10  *
  11  * Inspiration, some code, and most witty comments come from
  12  * Documentation/virtual/lguest/lguest.c, by Rusty Russell
  13  *
  14  * This work is licensed under the terms of the GNU GPL, version 2.
  15  */
  16
  17 #include "trace.h"
  18 #include "hw/hw.h"
  19 #include "exec/memory.h"
  20 #include "exec/address-spaces.h"
  21 #include "hw/virtio/virtio-access.h"
  22 #include "hw/virtio/dataplane/vring.h"
  23 #include "hw/virtio/dataplane/vring-accessors.h"
  24 #include "qemu/error-report.h"
  25
  26 /* vring_map can be coupled with vring_unmap or (if you still have the
  27  * value returned in *mr) memory_region_unref.
  28  */
  29 static void *vring_map(MemoryRegion **mr, hwaddr phys, hwaddr len,
  30                        bool is_write)
  31 {
  32     MemoryRegionSection section = memory_region_find(get_system_memory(), phys, len);
  33
  34     if (!section.mr || int128_get64(section.size) < len) {
  35         goto out;
  36     }
  37     if (is_write && section.readonly) {
  38         goto out;
  39     }
  40     if (!memory_region_is_ram(section.mr)) {
  41         goto out;
  42     }
  43
  44     /* Ignore regions with dirty logging, we cannot mark them dirty */
  45     if (memory_region_is_logging(section.mr)) {
  46         goto out;
  47     }
  48
  49     *mr = section.mr;
  50     return memory_region_get_ram_ptr(section.mr) + section.offset_within_region;
  51
  52 out:
  53     memory_region_unref(section.mr);
  54     *mr = NULL;
  55     return NULL;
  56 }
  57
  58 static void vring_unmap(void *buffer, bool is_write)
  59 {
  60     ram_addr_t addr;
  61     MemoryRegion *mr;
  62
  63     mr = qemu_ram_addr_from_host(buffer, &addr);
  64     memory_region_unref(mr);
  65 }
  66
  67 /* Map the guest's vring to host memory */
  68 bool vring_setup(Vring *vring, VirtIODevice *vdev, int n)
  69 {
  70     hwaddr vring_addr = virtio_queue_get_ring_addr(vdev, n);
  71     hwaddr vring_size = virtio_queue_get_ring_size(vdev, n);
  72     void *vring_ptr;
  73
  74     vring->broken = false;
  75
  76     vring_ptr = vring_map(&vring->mr, vring_addr, vring_size, true);
  77     if (!vring_ptr) {
  78         error_report("Failed to map vring "
  79                      "addr %#" HWADDR_PRIx " size %" HWADDR_PRIu,
  80                      vring_addr, vring_size);
  81         vring->broken = true;
  82         return false;
  83     }
  84
  85     vring_init(&vring->vr, virtio_queue_get_num(vdev, n), vring_ptr, 4096);
  86
  87     vring->last_avail_idx = virtio_queue_get_last_avail_idx(vdev, n);
  88     vring->last_used_idx = vring_get_used_idx(vdev, vring);
  89     vring->signalled_used = 0;
  90     vring->signalled_used_valid = false;
  91
  92     trace_vring_setup(virtio_queue_get_ring_addr(vdev, n),
  93                       vring->vr.desc, vring->vr.avail, vring->vr.used);
  94     return true;
  95 }
  96
  97 void vring_teardown(Vring *vring, VirtIODevice *vdev, int n)
  98 {
  99     virtio_queue_set_last_avail_idx(vdev, n, vring->last_avail_idx);
 100     virtio_queue_invalidate_signalled_used(vdev, n);
 101
 102     memory_region_unref(vring->mr);
 103 }
 104
 105 /* Disable guest->host notifies */
 106 void vring_disable_notification(VirtIODevice *vdev, Vring *vring)
 107 {
 108     if (!virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX)) {
 109         vring_set_used_flags(vdev, vring, VRING_USED_F_NO_NOTIFY);
 110     }
 111 }
 112
 113 /* Enable guest->host notifies
 114  *
 115  * Return true if the vring is empty, false if there are more requests.
 116  */
 117 bool vring_enable_notification(VirtIODevice *vdev, Vring *vring)
 118 {
 119     if (virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX)) {
 120         vring_avail_event(&vring->vr) = vring->vr.avail->idx;
 121     } else {
 122         vring_clear_used_flags(vdev, vring, VRING_USED_F_NO_NOTIFY);
 123     }
 124     smp_mb(); /* ensure update is seen before reading avail_idx */
 125     return !vring_more_avail(vdev, vring);
 126 }
 127
 128 /* This is stolen from linux/drivers/vhost/vhost.c:vhost_notify() */
 129 bool vring_should_notify(VirtIODevice *vdev, Vring *vring)
 130 {
 131     uint16_t old, new;
 132     bool v;
 133     /* Flush out used index updates. This is paired
 134      * with the barrier that the Guest executes when enabling
 135      * interrupts. */
 136     smp_mb();
 137
 138     if (virtio_has_feature(vdev, VIRTIO_F_NOTIFY_ON_EMPTY) &&
 139         unlikely(!vring_more_avail(vdev, vring))) {
 140         return true;
 141     }
 142
 143     if (!virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX)) {
 144         return !(vring_get_avail_flags(vdev, vring) &
 145                  VRING_AVAIL_F_NO_INTERRUPT);
 146     }
 147     old = vring->signalled_used;
 148     v = vring->signalled_used_valid;
 149     new = vring->signalled_used = vring->last_used_idx;
 150     vring->signalled_used_valid = true;
 151
 152     if (unlikely(!v)) {
 153         return true;
 154     }
 155
 156     return vring_need_event(vring_used_event(&vring->vr), new, old);
 157 }
 158
 159
 160 static int get_desc(Vring *vring, VirtQueueElement *elem,
 161                     struct vring_desc *desc)
 162 {
 163     unsigned *num;
 164     struct iovec *iov;
 165     hwaddr *addr;
 166     MemoryRegion *mr;
 167
 168     if (desc->flags & VRING_DESC_F_WRITE) {
 169         num = &elem->in_num;
 170         iov = &elem->in_sg[*num];
 171         addr = &elem->in_addr[*num];
 172     } else {
 173         num = &elem->out_num;
 174         iov = &elem->out_sg[*num];
 175         addr = &elem->out_addr[*num];
 176
 177         /* If it's an output descriptor, they're all supposed
 178          * to come before any input descriptors. */
 179         if (unlikely(elem->in_num)) {
 180             error_report("Descriptor has out after in");
 181             return -EFAULT;
 182         }
 183     }
 184
 185     /* Stop for now if there are not enough iovecs available. */
 186     if (*num >= VIRTQUEUE_MAX_SIZE) {
 187         error_report("Invalid SG num: %u", *num);
 188         return -EFAULT;
 189     }
 190
 191     /* TODO handle non-contiguous memory across region boundaries */
 192     iov->iov_base = vring_map(&mr, desc->addr, desc->len,
 193                               desc->flags & VRING_DESC_F_WRITE);
 194     if (!iov->iov_base) {
 195         error_report("Failed to map descriptor addr %#" PRIx64 " len %u",
 196                      (uint64_t)desc->addr, desc->len);
 197         return -EFAULT;
 198     }
 199
 200     /* The MemoryRegion is looked up again and unref'ed later, leave the
 201      * ref in place.  */
 202     iov->iov_len = desc->len;
 203     *addr = desc->addr;
 204     *num += 1;
 205     return 0;
 206 }
 207
 208 static void copy_in_vring_desc(VirtIODevice *vdev,
 209                                const struct vring_desc *guest,
 210                                struct vring_desc *host)
 211 {
 212     host->addr = virtio_ldq_p(vdev, &guest->addr);
 213     host->len = virtio_ldl_p(vdev, &guest->len);
 214     host->flags = virtio_lduw_p(vdev, &guest->flags);
 215     host->next = virtio_lduw_p(vdev, &guest->next);
 216 }
 217
 218 /* This is stolen from linux/drivers/vhost/vhost.c. */
 219 static int get_indirect(VirtIODevice *vdev, Vring *vring,
 220                         VirtQueueElement *elem, struct vring_desc *indirect)
 221 {
 222     struct vring_desc desc;
 223     unsigned int i = 0, count, found = 0;
 224     int ret;
 225
 226     /* Sanity check */
 227     if (unlikely(indirect->len % sizeof(desc))) {
 228         error_report("Invalid length in indirect descriptor: "
 229                      "len %#x not multiple of %#zx",
 230                      indirect->len, sizeof(desc));
 231         vring->broken = true;
 232         return -EFAULT;
 233     }
 234
 235     count = indirect->len / sizeof(desc);
 236     /* Buffers are chained via a 16 bit next field, so
 237      * we can have at most 2^16 of these. */
 238     if (unlikely(count > USHRT_MAX + 1)) {
 239         error_report("Indirect buffer length too big: %d", indirect->len);
 240         vring->broken = true;
 241         return -EFAULT;
 242     }
 243
 244     do {
 245         struct vring_desc *desc_ptr;
 246         MemoryRegion *mr;
 247
 248         /* Translate indirect descriptor */
 249         desc_ptr = vring_map(&mr,
 250                              indirect->addr + found * sizeof(desc),
 251                              sizeof(desc), false);
 252         if (!desc_ptr) {
 253             error_report("Failed to map indirect descriptor "
 254                          "addr %#" PRIx64 " len %zu",
 255                          (uint64_t)indirect->addr + found * sizeof(desc),
 256                          sizeof(desc));
 257             vring->broken = true;
 258             return -EFAULT;
 259         }
 260         copy_in_vring_desc(vdev, desc_ptr, &desc);
 261         memory_region_unref(mr);
 262
 263         /* Ensure descriptor has been loaded before accessing fields */
 264         barrier(); /* read_barrier_depends(); */
 265
 266         if (unlikely(++found > count)) {
 267             error_report("Loop detected: last one at %u "
 268                          "indirect size %u", i, count);
 269             vring->broken = true;
 270             return -EFAULT;
 271         }
 272
 273         if (unlikely(desc.flags & VRING_DESC_F_INDIRECT)) {
 274             error_report("Nested indirect descriptor");
 275             vring->broken = true;
 276             return -EFAULT;
 277         }
 278
 279         ret = get_desc(vring, elem, &desc);
 280         if (ret < 0) {
 281             vring->broken |= (ret == -EFAULT);
 282             return ret;
 283         }
 284         i = desc.next;
 285     } while (desc.flags & VRING_DESC_F_NEXT);
 286     return 0;
 287 }
 288
 289 static void vring_unmap_element(VirtQueueElement *elem)
 290 {
 291     int i;
 292
 293     /* This assumes that the iovecs, if changed, are never moved past
 294      * the end of the valid area.  This is true if iovec manipulations
 295      * are done with iov_discard_front and iov_discard_back.
 296      */
 297     for (i = 0; i < elem->out_num; i++) {
 298         vring_unmap(elem->out_sg[i].iov_base, false);
 299     }
 300
 301     for (i = 0; i < elem->in_num; i++) {
 302         vring_unmap(elem->in_sg[i].iov_base, true);
 303     }
 304 }
 305
 306 /* This looks in the virtqueue and for the first available buffer, and converts
 307  * it to an iovec for convenient access.  Since descriptors consist of some
 308  * number of output then some number of input descriptors, it's actually two
 309  * iovecs, but we pack them into one and note how many of each there were.
 310  *
 311  * This function returns the descriptor number found, or vq->num (which is
 312  * never a valid descriptor number) if none was found.  A negative code is
 313  * returned on error.
 314  *
 315  * Stolen from linux/drivers/vhost/vhost.c.
 316  */
 317 int vring_pop(VirtIODevice *vdev, Vring *vring,
 318               VirtQueueElement *elem)
 319 {
 320     struct vring_desc desc;
 321     unsigned int i, head, found = 0, num = vring->vr.num;
 322     uint16_t avail_idx, last_avail_idx;
 323     int ret;
 324
 325     /* Initialize elem so it can be safely unmapped */
 326     elem->in_num = elem->out_num = 0;
 327
 328     /* If there was a fatal error then refuse operation */
 329     if (vring->broken) {
 330         ret = -EFAULT;
 331         goto out;
 332     }
 333
 334     /* Check it isn't doing very strange things with descriptor numbers. */
 335     last_avail_idx = vring->last_avail_idx;
 336     avail_idx = vring_get_avail_idx(vdev, vring);
 337     barrier(); /* load indices now and not again later */
 338
 339     if (unlikely((uint16_t)(avail_idx - last_avail_idx) > num)) {
 340         error_report("Guest moved used index from %u to %u",
 341                      last_avail_idx, avail_idx);
 342         ret = -EFAULT;
 343         goto out;
 344     }
 345
 346     /* If there's nothing new since last we looked. */
 347     if (avail_idx == last_avail_idx) {
 348         ret = -EAGAIN;
 349         goto out;
 350     }
 351
 352     /* Only get avail ring entries after they have been exposed by guest. */
 353     smp_rmb();
 354
 355     /* Grab the next descriptor number they're advertising, and increment
 356      * the index we've seen. */
 357     head = vring_get_avail_ring(vdev, vring, last_avail_idx % num);
 358
 359     elem->index = head;
 360
 361     /* If their number is silly, that's an error. */
 362     if (unlikely(head >= num)) {
 363         error_report("Guest says index %u > %u is available", head, num);
 364         ret = -EFAULT;
 365         goto out;
 366     }
 367
 368     i = head;
 369     do {
 370         if (unlikely(i >= num)) {
 371             error_report("Desc index is %u > %u, head = %u", i, num, head);
 372             ret = -EFAULT;
 373             goto out;
 374         }
 375         if (unlikely(++found > num)) {
 376             error_report("Loop detected: last one at %u vq size %u head %u",
 377                          i, num, head);
 378             ret = -EFAULT;
 379             goto out;
 380         }
 381         copy_in_vring_desc(vdev, &vring->vr.desc[i], &desc);
 382
 383         /* Ensure descriptor is loaded before accessing fields */
 384         barrier();
 385
 386         if (desc.flags & VRING_DESC_F_INDIRECT) {
 387             ret = get_indirect(vdev, vring, elem, &desc);
 388             if (ret < 0) {
 389                 goto out;
 390             }
 391             continue;
 392         }
 393
 394         ret = get_desc(vring, elem, &desc);
 395         if (ret < 0) {
 396             goto out;
 397         }
 398
 399         i = desc.next;
 400     } while (desc.flags & VRING_DESC_F_NEXT);
 401
 402     /* On success, increment avail index. */
 403     vring->last_avail_idx++;
 404     if (virtio_has_feature(vdev, VIRTIO_RING_F_EVENT_IDX)) {
 405         vring_avail_event(&vring->vr) = vring->last_avail_idx;
 406     }
 407
 408     return head;
 409
 410 out:
 411     assert(ret < 0);
 412     if (ret == -EFAULT) {
 413         vring->broken = true;
 414     }
 415     vring_unmap_element(elem);
 416     return ret;
 417 }
 418
 419 /* After we've used one of their buffers, we tell them about it.
 420  *
 421  * Stolen from linux/drivers/vhost/vhost.c.
 422  */
 423 void vring_push(VirtIODevice *vdev, Vring *vring, VirtQueueElement *elem,
 424                 int len)
 425 {
 426     unsigned int head = elem->index;
 427     uint16_t new;
 428
 429     vring_unmap_element(elem);
 430
 431     /* Don't touch vring if a fatal error occurred */
 432     if (vring->broken) {
 433         return;
 434     }
 435
 436     /* The virtqueue contains a ring of used buffers.  Get a pointer to the
 437      * next entry in that used ring. */
 438     vring_set_used_ring_id(vdev, vring, vring->last_used_idx % vring->vr.num,
 439                            head);
 440     vring_set_used_ring_len(vdev, vring, vring->last_used_idx % vring->vr.num,
 441                             len);
 442
 443     /* Make sure buffer is written before we update index. */
 444     smp_wmb();
 445
 446     new = ++vring->last_used_idx;
 447     vring_set_used_idx(vdev, vring, new);
 448     if (unlikely((int16_t)(new - vring->signalled_used) < (uint16_t)1)) {
 449         vring->signalled_used_valid = false;
 450     }
 451 }