Re: [PATCH v7 08/12] vdpa: Move command buffers map to start of net device

[Jason Wang]

On Fri, Aug 5, 2022 at 2:29 AM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> As this series will reuse them to restore the device state at the end of
> a migration (or a device start), let's allocate only once at the device
> start so we don't duplicate their map and unmap.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  net/vhost-vdpa.c | 123 ++++++++++++++++++++++-------------------------
>  1 file changed, 58 insertions(+), 65 deletions(-)
>
> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> index 55e8a39a56..2c6a26cca0 100644
> --- a/net/vhost-vdpa.c
> +++ b/net/vhost-vdpa.c
> @@ -263,29 +263,20 @@ static size_t vhost_vdpa_net_cvq_cmd_page_len(void)
>      return ROUND_UP(vhost_vdpa_net_cvq_cmd_len(), 
> qemu_real_host_page_size());
>  }
>
> -/** Copy and map a guest buffer. */
> -static bool vhost_vdpa_cvq_map_buf(struct vhost_vdpa *v,
> -                                   const struct iovec *out_data,
> -                                   size_t out_num, size_t data_len, void 
> *buf,
> -                                   size_t *written, bool write)
> +/** Map CVQ buffer. */
> +static int vhost_vdpa_cvq_map_buf(struct vhost_vdpa *v, void *buf, size_t 
> size,
> +                                  bool write)
>  {
>      DMAMap map = {};
>      int r;
>
> -    if (unlikely(!data_len)) {
> -        qemu_log_mask(LOG_GUEST_ERROR, "%s: invalid legnth of %s buffer\n",
> -                      __func__, write ? "in" : "out");
> -        return false;
> -    }
> -
> -    *written = iov_to_buf(out_data, out_num, 0, buf, data_len);
>      map.translated_addr = (hwaddr)(uintptr_t)buf;
> -    map.size = vhost_vdpa_net_cvq_cmd_page_len() - 1;
> +    map.size = size - 1;

Just noticed this, I think I've asked for the reason before but I
don't remember the answer.

But it looks like a hint of a defect of the current API design.

Thanks

>      map.perm = write ? IOMMU_RW : IOMMU_RO,
>      r = vhost_iova_tree_map_alloc(v->iova_tree, &map);
>      if (unlikely(r != IOVA_OK)) {
>          error_report("Cannot map injected element");
> -        return false;
> +        return r;
>      }
>
>      r = vhost_vdpa_dma_map(v, map.iova, vhost_vdpa_net_cvq_cmd_page_len(), 
> buf,
> @@ -294,50 +285,58 @@ static bool vhost_vdpa_cvq_map_buf(struct vhost_vdpa *v,
>          goto dma_map_err;
>      }
>
> -    return true;
> +    return 0;
>
>  dma_map_err:
>      vhost_iova_tree_remove(v->iova_tree, &map);
> -    return false;
> +    return r;
>  }
>
> -/**
> - * Copy the guest element into a dedicated buffer suitable to be sent to NIC
> - *
> - * @iov: [0] is the out buffer, [1] is the in one
> - */
> -static bool vhost_vdpa_net_cvq_map_elem(VhostVDPAState *s,
> -                                        VirtQueueElement *elem,
> -                                        struct iovec *iov)
> +static int vhost_vdpa_net_cvq_prepare(NetClientState *nc)
>  {
> -    size_t in_copied;
> -    bool ok;
> +    VhostVDPAState *s;
> +    int r;
>
> -    iov[0].iov_base = s->cvq_cmd_out_buffer;
> -    ok = vhost_vdpa_cvq_map_buf(&s->vhost_vdpa, elem->out_sg, elem->out_num,
> -                                vhost_vdpa_net_cvq_cmd_len(), 
> iov[0].iov_base,
> -                                &iov[0].iov_len, false);
> -    if (unlikely(!ok)) {
> -        return false;
> +    assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
> +
> +    s = DO_UPCAST(VhostVDPAState, nc, nc);
> +    if (!s->vhost_vdpa.shadow_vqs_enabled) {
> +        return 0;
>      }
>
> -    iov[1].iov_base = s->cvq_cmd_in_buffer;
> -    ok = vhost_vdpa_cvq_map_buf(&s->vhost_vdpa, NULL, 0,
> -                                sizeof(virtio_net_ctrl_ack), iov[1].iov_base,
> -                                &in_copied, true);
> -    if (unlikely(!ok)) {
> +    r = vhost_vdpa_cvq_map_buf(&s->vhost_vdpa, s->cvq_cmd_out_buffer,
> +                               vhost_vdpa_net_cvq_cmd_page_len(), false);
> +    if (unlikely(r < 0)) {
> +        return r;
> +    }
> +
> +    r = vhost_vdpa_cvq_map_buf(&s->vhost_vdpa, s->cvq_cmd_in_buffer,
> +                               vhost_vdpa_net_cvq_cmd_page_len(), true);
> +    if (unlikely(r < 0)) {
>          vhost_vdpa_cvq_unmap_buf(&s->vhost_vdpa, s->cvq_cmd_out_buffer);
> -        return false;
>      }
>
> -    iov[1].iov_len = sizeof(virtio_net_ctrl_ack);
> -    return true;
> +    return r;
> +}
> +
> +static void vhost_vdpa_net_cvq_stop(NetClientState *nc)
> +{
> +    VhostVDPAState *s = DO_UPCAST(VhostVDPAState, nc, nc);
> +
> +    assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
> +
> +    if (s->vhost_vdpa.shadow_vqs_enabled) {
> +        vhost_vdpa_cvq_unmap_buf(&s->vhost_vdpa, s->cvq_cmd_out_buffer);
> +        vhost_vdpa_cvq_unmap_buf(&s->vhost_vdpa, s->cvq_cmd_in_buffer);
> +    }
>  }
>
>  static NetClientInfo net_vhost_vdpa_cvq_info = {
>      .type = NET_CLIENT_DRIVER_VHOST_VDPA,
>      .size = sizeof(VhostVDPAState),
>      .receive = vhost_vdpa_receive,
> +    .prepare = vhost_vdpa_net_cvq_prepare,
> +    .stop = vhost_vdpa_net_cvq_stop,
>      .cleanup = vhost_vdpa_cleanup,
>      .has_vnet_hdr = vhost_vdpa_has_vnet_hdr,
>      .has_ufo = vhost_vdpa_has_ufo,
> @@ -348,19 +347,17 @@ static NetClientInfo net_vhost_vdpa_cvq_info = {
>   * Do not forward commands not supported by SVQ. Otherwise, the device could
>   * accept it and qemu would not know how to update the device model.
>   */
> -static bool vhost_vdpa_net_cvq_validate_cmd(const struct iovec *out,
> -                                            size_t out_num)
> +static bool vhost_vdpa_net_cvq_validate_cmd(const void *out_buf, size_t len)
>  {
>      struct virtio_net_ctrl_hdr ctrl;
> -    size_t n;
>
> -    n = iov_to_buf(out, out_num, 0, &ctrl, sizeof(ctrl));
> -    if (unlikely(n < sizeof(ctrl))) {
> +    if (unlikely(len < sizeof(ctrl))) {
>          qemu_log_mask(LOG_GUEST_ERROR,
> -                      "%s: invalid legnth of out buffer %zu\n", __func__, n);
> +                      "%s: invalid legnth of out buffer %zu\n", __func__, 
> len);
>          return false;
>      }
>
> +    memcpy(&ctrl, out_buf, sizeof(ctrl));
>      switch (ctrl.class) {
>      case VIRTIO_NET_CTRL_MAC:
>          switch (ctrl.cmd) {
> @@ -392,10 +389,14 @@ static int 
> vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
>      VhostVDPAState *s = opaque;
>      size_t in_len, dev_written;
>      virtio_net_ctrl_ack status = VIRTIO_NET_ERR;
> -    /* out and in buffers sent to the device */
> -    struct iovec dev_buffers[2] = {
> -        { .iov_base = s->cvq_cmd_out_buffer },
> -        { .iov_base = s->cvq_cmd_in_buffer },
> +    /* Out buffer sent to both the vdpa device and the device model */
> +    struct iovec out = {
> +        .iov_base = s->cvq_cmd_out_buffer,
> +    };
> +    /* In buffer sent to the device */
> +    const struct iovec dev_in = {
> +        .iov_base = s->cvq_cmd_in_buffer,
> +        .iov_len = sizeof(virtio_net_ctrl_ack),
>      };
>      /* in buffer used for device model */
>      const struct iovec in = {
> @@ -405,17 +406,15 @@ static int 
> vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
>      int r = -EINVAL;
>      bool ok;
>
> -    ok = vhost_vdpa_net_cvq_map_elem(s, elem, dev_buffers);
> -    if (unlikely(!ok)) {
> -        goto out;
> -    }
> -
> -    ok = vhost_vdpa_net_cvq_validate_cmd(&dev_buffers[0], 1);
> +    out.iov_len = iov_to_buf(elem->out_sg, elem->out_num, 0,
> +                             s->cvq_cmd_out_buffer,
> +                             vhost_vdpa_net_cvq_cmd_len());
> +    ok = vhost_vdpa_net_cvq_validate_cmd(s->cvq_cmd_out_buffer, out.iov_len);
>      if (unlikely(!ok)) {
>          goto out;
>      }
>
> -    r = vhost_svq_add(svq, &dev_buffers[0], 1, &dev_buffers[1], 1, elem);
> +    r = vhost_svq_add(svq, &out, 1, &dev_in, 1, elem);
>      if (unlikely(r != 0)) {
>          if (unlikely(r == -ENOSPC)) {
>              qemu_log_mask(LOG_GUEST_ERROR, "%s: No space on device queue\n",
> @@ -435,13 +434,13 @@ static int 
> vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
>          goto out;
>      }
>
> -    memcpy(&status, dev_buffers[1].iov_base, sizeof(status));
> +    memcpy(&status, s->cvq_cmd_in_buffer, sizeof(status));
>      if (status != VIRTIO_NET_OK) {
>          goto out;
>      }
>
>      status = VIRTIO_NET_ERR;
> -    virtio_net_handle_ctrl_iov(svq->vdev, &in, 1, dev_buffers, 1);
> +    virtio_net_handle_ctrl_iov(svq->vdev, &in, 1, &out, 1);
>      if (status != VIRTIO_NET_OK) {
>          error_report("Bad CVQ processing in model");
>      }
> @@ -454,12 +453,6 @@ out:
>      }
>      vhost_svq_push_elem(svq, elem, MIN(in_len, sizeof(status)));
>      g_free(elem);
> -    if (dev_buffers[0].iov_base) {
> -        vhost_vdpa_cvq_unmap_buf(&s->vhost_vdpa, dev_buffers[0].iov_base);
> -    }
> -    if (dev_buffers[1].iov_base) {
> -        vhost_vdpa_cvq_unmap_buf(&s->vhost_vdpa, dev_buffers[1].iov_base);
> -    }
>      return r;
>  }
>
> --
> 2.31.1
>