Re: [PATCH] vdpa: fix emulated guest announce feature status handling

[Eugenio Perez Martin]

On Fri, Mar 3, 2023 at 12:58 PM Gautam Dawar <gautam.dawar@amd.com> wrote:
>
> Guest announce capability is emulated by qemu in the .avail_handler
> shadow virtqueue operation. It updates the status to success in
> `*s->status` but incorrectly fetches the command execution
> status from local variable `status` later in call to iov_from_buf().
> As `status` is initialized to VIRTIO_NET_ERR, it results in a
> warning "Failed to ack link announce" in virtio_net driver's
> virtnet_ack_link_announce() function after VM Live Migration.
> Also, I noticed an invalid check in vhost_vdpa_net_handle_ctrl_avail()
> that reports an error because status is not updated in call to
> virtio_net_handle_ctrl_iov():
>

status should be updated through &in. It is declared as:
const struct iovec in = {
        .iov_base = &status,
        .iov_len = sizeof(status),
    };

And it should be filled at the end of virtio_net_handle_ctrl_iov with a call to:
    s = iov_from_buf(in_sg, in_num, 0, &status, sizeof(status));

How do you obtain different values? Maybe const optimizations is
invalid and the compiler thinks virtio_net_handle_ctrl_iov will never
change status?

Thanks!

>     virtio_net_handle_ctrl_iov(svq->vdev, &in, 1, &out, 1);
>     if (status != VIRTIO_NET_OK) {
>         error_report("Bad CVQ processing in model");
>     }
> Adding an optional OUT status parameter to virtio_net_handle_ctrl_iov()
> would help resolving this issue and also send the correct status
> value to the virtio-net driver.
>
> Signed-off-by: Gautam Dawar <gautam.dawar@amd.com>
> ---
>  hw/net/virtio-net.c            | 9 +++++++--
>  include/hw/virtio/virtio-net.h | 3 ++-
>  net/vhost-vdpa.c               | 3 +--
>  3 files changed, 10 insertions(+), 5 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 3ae909041a..36a75592da 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -1503,7 +1503,8 @@ static int virtio_net_handle_mq(VirtIONet *n, uint8_t 
> cmd,
>  size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
>                                    const struct iovec *in_sg, unsigned in_num,
>                                    const struct iovec *out_sg,
> -                                  unsigned out_num)
> +                                  unsigned out_num,
> +                                 virtio_net_ctrl_ack *status_out)
>  {
>      VirtIONet *n = VIRTIO_NET(vdev);
>      struct virtio_net_ctrl_hdr ctrl;
> @@ -1514,6 +1515,8 @@ size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
>      if (iov_size(in_sg, in_num) < sizeof(status) ||
>          iov_size(out_sg, out_num) < sizeof(ctrl)) {
>          virtio_error(vdev, "virtio-net ctrl missing headers");
> +       if (status_out)
> +               *status_out = status;
>          return 0;
>      }
>
> @@ -1540,6 +1543,8 @@ size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
>      assert(s == sizeof(status));
>
>      g_free(iov2);
> +    if (status_out)
> +           *status_out = status;
>      return sizeof(status);
>  }
>
> @@ -1555,7 +1560,7 @@ static void virtio_net_handle_ctrl(VirtIODevice *vdev, 
> VirtQueue *vq)
>          }
>
>          written = virtio_net_handle_ctrl_iov(vdev, elem->in_sg, elem->in_num,
> -                                             elem->out_sg, elem->out_num);
> +                                             elem->out_sg, elem->out_num, 
> NULL);
>          if (written > 0) {
>              virtqueue_push(vq, elem, written);
>              virtio_notify(vdev, vq);
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index ef234ffe7e..da76cc414d 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -224,7 +224,8 @@ struct VirtIONet {
>  size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
>                                    const struct iovec *in_sg, unsigned in_num,
>                                    const struct iovec *out_sg,
> -                                  unsigned out_num);
> +                                  unsigned out_num,
> +                                 virtio_net_ctrl_ack *status);
>  void virtio_net_set_netclient_name(VirtIONet *n, const char *name,
>                                     const char *type);
>
> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> index de5ed8ff22..c72b338633 100644
> --- a/net/vhost-vdpa.c
> +++ b/net/vhost-vdpa.c
> @@ -638,8 +638,7 @@ static int 
> vhost_vdpa_net_handle_ctrl_avail(VhostShadowVirtqueue *svq,
>          return VIRTIO_NET_ERR;
>      }
>
> -    status = VIRTIO_NET_ERR;
> -    virtio_net_handle_ctrl_iov(svq->vdev, &in, 1, &out, 1);
> +    virtio_net_handle_ctrl_iov(svq->vdev, &in, 1, &out, 1, &status);
>      if (status != VIRTIO_NET_OK) {
>          error_report("Bad CVQ processing in model");
>      }
> --
> 2.30.1
>