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

[Eugenio Perez Martin]

On Tue, Aug 9, 2022 at 9:04 AM Jason Wang <jasowang@redhat.com> wrote:
>
> 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.
>

I can look for it in the mail list, but long story short:
vDPA DMA API is *not* inclusive: To map the first page, you map (.iova
= 0, .size = 4096).
IOVA tree API has been inclusive forever: To map the first page, you
map (.iova = 0, .size = 4095). If we map with .size = 4096, .iova =
4096 is considered mapped too.

To adapt one to the other would have been an API change even before
the introduction of vhost-iova-tree.

Thanks!


> 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
> >
>