text: /* Copyright 2012 Red Hat, Inc.
   * Copyright IBM, Corp. 2012
   *
   * Based on Linux 2.6.39 vhost code:
   * Copyright (C) 2009 Red Hat, Inc.
   * Copyright (C) 2006 Rusty Russell IBM Corporation
   *
   * Author: Michael S. Tsirkin <mst@redhat.com>
   *         Stefan Hajnoczi <stefanha@redhat.com>
   *
   * Inspiration, some code, and most witty comments come from
   * Documentation/virtual/lguest/lguest.c, by Rusty Russell
   *
   * This work is licensed under the terms of the GNU GPL, version 2.
   */
  
  #include "trace.h"
  #include "hw/virtio/dataplane/vring.h"
  #include "qemu/error-report.h"
  
  /* Map the guest's vring to host memory */
  bool vring_setup(Vring *vring, VirtIODevice *vdev, int n)
  {
      hwaddr vring_addr = virtio_queue_get_ring_addr(vdev, n);
      hwaddr vring_size = virtio_queue_get_ring_size(vdev, n);
      void *vring_ptr;
  
      vring->broken = false;
  
      hostmem_init(&vring->hostmem);
      vring_ptr = hostmem_lookup(&vring->hostmem, vring_addr, vring_size, true);
      if (!vring_ptr) {
          error_report("Failed to map vring "
                       "addr %#" HWADDR_PRIx " size %" HWADDR_PRIu,
                       vring_addr, vring_size);
          vring->broken = true;
          return false;
      }
  
      vring_init(&vring->vr, virtio_queue_get_num(vdev, n), vring_ptr, 4096);
  
      vring->last_avail_idx = virtio_queue_get_last_avail_idx(vdev, n);
      vring->last_used_idx = vring->vr.used->idx;
      vring->signalled_used = 0;
      vring->signalled_used_valid = false;
  
      trace_vring_setup(virtio_queue_get_ring_addr(vdev, n),
                        vring->vr.desc, vring->vr.avail, vring->vr.used);
      return true;
  }
  
  void vring_teardown(Vring *vring, VirtIODevice *vdev, int n)
  {
      virtio_queue_set_last_avail_idx(vdev, n, vring->last_avail_idx);
      virtio_queue_invalidate_signalled_used(vdev, n);
  
      hostmem_finalize(&vring->hostmem);
  }
  
  /* Disable guest->host notifies */
  void vring_disable_notification(VirtIODevice *vdev, Vring *vring)
  {
      if (!(vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX))) {
          vring->vr.used->flags |= VRING_USED_F_NO_NOTIFY;
      }
  }
  
  /* Enable guest->host notifies
   *
   * Return true if the vring is empty, false if there are more requests.
   */
  bool vring_enable_notification(VirtIODevice *vdev, Vring *vring)
  {
      if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
          vring_avail_event(&vring->vr) = vring->vr.avail->idx;
      } else {
          vring->vr.used->flags &= ~VRING_USED_F_NO_NOTIFY;
      }
      smp_mb(); /* ensure update is seen before reading avail_idx */
      return !vring_more_avail(vring);
  }
  
  /* This is stolen from linux/drivers/vhost/vhost.c:vhost_notify() */
  bool vring_should_notify(VirtIODevice *vdev, Vring *vring)
  {
      uint16_t old, new;
      bool v;
      /* Flush out used index updates. This is paired
       * with the barrier that the Guest executes when enabling
       * interrupts. */
      smp_mb();
  
      if ((vdev->guest_features & VIRTIO_F_NOTIFY_ON_EMPTY) &&
          unlikely(vring->vr.avail->idx == vring->last_avail_idx)) {
          return true;
      }
  
      if (!(vdev->guest_features & VIRTIO_RING_F_EVENT_IDX)) {
          return !(vring->vr.avail->flags & VRING_AVAIL_F_NO_INTERRUPT);
      }
      old = vring->signalled_used;
      v = vring->signalled_used_valid;
      new = vring->signalled_used = vring->last_used_idx;
      vring->signalled_used_valid = true;
  
      if (unlikely(!v)) {
          return true;
      }
  
      return vring_need_event(vring_used_event(&vring->vr), new, old);
  }
  
  /* This is stolen from linux/drivers/vhost/vhost.c. */
  static int get_indirect(Vring *vring,
                          struct iovec iov[], struct iovec *iov_end,
                          unsigned int *out_num, unsigned int *in_num,
                          struct vring_desc *indirect)
  {
      struct vring_desc desc;
      unsigned int i = 0, count, found = 0;
  
      /* Sanity check */
      if (unlikely(indirect->len % sizeof(desc))) {
          error_report("Invalid length in indirect descriptor: "
                       "len %#x not multiple of %#zx",
                       indirect->len, sizeof(desc));
          vring->broken = true;
          return -EFAULT;
      }
  
      count = indirect->len / sizeof(desc);
      /* Buffers are chained via a 16 bit next field, so
       * we can have at most 2^16 of these. */
      if (unlikely(count > USHRT_MAX + 1)) {
          error_report("Indirect buffer length too big: %d", indirect->len);
          vring->broken = true;
          return -EFAULT;
      }
  
      do {
          struct vring_desc *desc_ptr;
  
          /* Translate indirect descriptor */
          desc_ptr = hostmem_lookup(&vring->hostmem,
                                    indirect->addr + found * sizeof(desc),
                                    sizeof(desc), false);
          if (!desc_ptr) {
              error_report("Failed to map indirect descriptor "
                           "addr %#" PRIx64 " len %zu",
                           (uint64_t)indirect->addr + found * sizeof(desc),
                           sizeof(desc));
              vring->broken = true;
              return -EFAULT;
          }
          desc = *desc_ptr;
  
          /* Ensure descriptor has been loaded before accessing fields */
          barrier(); /* read_barrier_depends(); */
  
          if (unlikely(++found > count)) {
              error_report("Loop detected: last one at %u "
                           "indirect size %u", i, count);
              vring->broken = true;
              return -EFAULT;
          }
  
          if (unlikely(desc.flags & VRING_DESC_F_INDIRECT)) {
              error_report("Nested indirect descriptor");
              vring->broken = true;
              return -EFAULT;
          }
  
          /* Stop for now if there are not enough iovecs available. */
          if (iov >= iov_end) {
              return -ENOBUFS;
          }
  
          iov->iov_base = hostmem_lookup(&vring->hostmem, desc.addr, desc.len,
                                         desc.flags & VRING_DESC_F_WRITE);
          if (!iov->iov_base) {
              error_report("Failed to map indirect descriptor"
                           "addr %#" PRIx64 " len %u",
                           (uint64_t)desc.addr, desc.len);
              vring->broken = true;
              return -EFAULT;
          }
          iov->iov_len = desc.len;
          iov++;
  
          /* If this is an input descriptor, increment that count. */
          if (desc.flags & VRING_DESC_F_WRITE) {
              *in_num += 1;
          } else {
              /* If it's an output descriptor, they're all supposed
               * to come before any input descriptors. */
              if (unlikely(*in_num)) {
                  error_report("Indirect descriptor "
                               "has out after in: idx %u", i);
                  vring->broken = true;
                  return -EFAULT;
              }
              *out_num += 1;
          }
          i = desc.next;
      } while (desc.flags & VRING_DESC_F_NEXT);
      return 0;
  }
  
  /* This looks in the virtqueue and for the first available buffer, and converts
   * it to an iovec for convenient access.  Since descriptors consist of some
   * number of output then some number of input descriptors, it's actually two
   * iovecs, but we pack them into one and note how many of each there were.
   *
   * This function returns the descriptor number found, or vq->num (which is
   * never a valid descriptor number) if none was found.  A negative code is
   * returned on error.
   *
   * Stolen from linux/drivers/vhost/vhost.c.
   */
  int vring_pop(VirtIODevice *vdev, Vring *vring,
                struct iovec iov[], struct iovec *iov_end,
                unsigned int *out_num, unsigned int *in_num)
  {
      struct vring_desc desc;
      unsigned int i, head, found = 0, num = vring->vr.num;
      uint16_t avail_idx, last_avail_idx;
  
      /* If there was a fatal error then refuse operation */
      if (vring->broken) {
          return -EFAULT;
      }
  
      /* Check it isn't doing very strange things with descriptor numbers. */
      last_avail_idx = vring->last_avail_idx;
      avail_idx = vring->vr.avail->idx;
      barrier(); /* load indices now and not again later */
  
      if (unlikely((uint16_t)(avail_idx - last_avail_idx) > num)) {
          error_report("Guest moved used index from %u to %u",
                       last_avail_idx, avail_idx);
          vring->broken = true;
          return -EFAULT;
      }
  
      /* If there's nothing new since last we looked. */
      if (avail_idx == last_avail_idx) {
          return -EAGAIN;
      }
  
      /* Only get avail ring entries after they have been exposed by guest. */
      smp_rmb();
  
      /* Grab the next descriptor number they're advertising, and increment
       * the index we've seen. */
      head = vring->vr.avail->ring[last_avail_idx % num];
  
      /* If their number is silly, that's an error. */
      if (unlikely(head >= num)) {
          error_report("Guest says index %u > %u is available", head, num);
          vring->broken = true;
          return -EFAULT;
      }
  
      if (vdev->guest_features & (1 << VIRTIO_RING_F_EVENT_IDX)) {
          vring_avail_event(&vring->vr) = vring->vr.avail->idx;
      }
  
      /* When we start there are none of either input nor output. */
      *out_num = *in_num = 0;
  
      i = head;
      do {
          if (unlikely(i >= num)) {
              error_report("Desc index is %u > %u, head = %u", i, num, head);
              vring->broken = true;
              return -EFAULT;
          }
          if (unlikely(++found > num)) {
              error_report("Loop detected: last one at %u vq size %u head %u",
                           i, num, head);
              vring->broken = true;
              return -EFAULT;
          }
          desc = vring->vr.desc[i];
  
          /* Ensure descriptor is loaded before accessing fields */
          barrier();
  
          if (desc.flags & VRING_DESC_F_INDIRECT) {
              int ret = get_indirect(vring, iov, iov_end, out_num, in_num, &desc);
              if (ret < 0) {
                  return ret;
              }
              continue;
          }
  
          /* If there are not enough iovecs left, stop for now.  The caller
           * should check if there are more descs available once they have dealt
           * with the current set.
           */
          if (iov >= iov_end) {
              return -ENOBUFS;
          }
  
          /* TODO handle non-contiguous memory across region boundaries */
          iov->iov_base = hostmem_lookup(&vring->hostmem, desc.addr, desc.len,
                                         desc.flags & VRING_DESC_F_WRITE);
          if (!iov->iov_base) {
              error_report("Failed to map vring desc addr %#" PRIx64 " len %u",
                           (uint64_t)desc.addr, desc.len);
              vring->broken = true;
              return -EFAULT;
          }
          iov->iov_len  = desc.len;
          iov++;
  
          if (desc.flags & VRING_DESC_F_WRITE) {
              /* If this is an input descriptor,
               * increment that count. */
              *in_num += 1;
          } else {
              /* If it's an output descriptor, they're all supposed
               * to come before any input descriptors. */
              if (unlikely(*in_num)) {
                  error_report("Descriptor has out after in: idx %d", i);
                  vring->broken = true;
                  return -EFAULT;
              }
              *out_num += 1;
          }
          i = desc.next;
      } while (desc.flags & VRING_DESC_F_NEXT);
  
      /* On success, increment avail index. */
      vring->last_avail_idx++;
      return head;
  }
  
  /* After we've used one of their buffers, we tell them about it.
   *
   * Stolen from linux/drivers/vhost/vhost.c.
   */
  void vring_push(Vring *vring, unsigned int head, int len)
  {
      struct vring_used_elem *used;
      uint16_t new;
  
      /* Don't touch vring if a fatal error occurred */
      if (vring->broken) {
          return;
      }
  
      /* The virtqueue contains a ring of used buffers.  Get a pointer to the
       * next entry in that used ring. */
      used = &vring->vr.used->ring[vring->last_used_idx % vring->vr.num];
      used->id = head;
      used->len = len;
  
      /* Make sure buffer is written before we update index. */
      smp_wmb();
  
      new = vring->vr.used->idx = ++vring->last_used_idx;
      if (unlikely((int16_t)(new - vring->signalled_used) < (uint16_t)1)) {
          vring->signalled_used_valid = false;
      }
  }
  