Re: [PATCH V2] vhost_vdpa: no need to fetch vring base when poweroff

[Jason Wang <jasowang@redhat.com>]

On Mon, Jul 10, 2023 at 4:53 PM Zhu Lingshan <lingshan.zhu@intel.com> wrote:
>
> In the poweroff routine, no need to fetch last available index.
>

This is because there's no concept of shutdown in the vhost layer, it
only knows start and stop.

> This commit also provides a better debug message in the vhost
> caller vhost_virtqueue_stop,

A separate patch is better.

> because if vhost does not fetch
> the last avail idx successfully, maybe the device does not
> suspend, vhost will sync last avail idx to vring used idx as a
> work around, not a failure.

This only happens if we return a negative value?

>
> Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
> ---
>  hw/virtio/vhost-vdpa.c | 10 ++++++++++
>  hw/virtio/vhost.c      |  2 +-
>  2 files changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 3c575a9a6e..10b445f64e 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -26,6 +26,7 @@
>  #include "cpu.h"
>  #include "trace.h"
>  #include "qapi/error.h"
> +#include "sysemu/runstate.h"
>
>  /*
>   * Return one past the end of the end of section. Be careful with uint64_t
> @@ -1391,6 +1392,15 @@ static int vhost_vdpa_get_vring_base(struct vhost_dev *dev,
>      struct vhost_vdpa *v = dev->opaque;
>      int ret;
>
> +    if (runstate_check(RUN_STATE_SHUTDOWN)) {
> +        /*
> +         * Some devices do not support this call properly,
> +         * and we don't need to retrieve the indexes
> +         * if it is shutting down
> +         */
> +        return 0;

Checking runstate in the vhost code seems like a layer violation.

What happens without this patch?

Thanks

> +    }
> +
>      if (v->shadow_vqs_enabled) {
>          ring->num = virtio_queue_get_last_avail_idx(dev->vdev, ring->index);
>          return 0;
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 82394331bf..7dd90cff3a 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -1262,7 +1262,7 @@ void vhost_virtqueue_stop(struct vhost_dev *dev,
>
>      r = dev->vhost_ops->vhost_get_vring_base(dev, &state);
>      if (r < 0) {
> -        VHOST_OPS_DEBUG(r, "vhost VQ %u ring restore failed: %d", idx, r);
> +        VHOST_OPS_DEBUG(r, "sync last avail idx to the guest used idx for vhost VQ %u", idx);
>          /* Connection to the backend is broken, so let's sync internal
>           * last avail idx to the device used idx.
>           */
> --
> 2.39.3
>