On Fri, Jul 5, 2024 at 6:09 PM Michael S. Tsirkin <mst@xxxxxxxxxx> wrote:
>
> QEMU implemented the configuration
> VIRTIO_BALLOON_F_REPORTING && ! VIRTIO_BALLOON_F_FREE_PAGE_HINT
> incorrectly: it then uses vq3 for reporting, spec says it is always 4.
>
> This is masked by a corresponding bug in driver:
> add a work around as I'm going to try and fix the driver bug.
>
> Signed-off-by: Michael S. Tsirkin <mst@xxxxxxxxxx>
> ---
> drivers/virtio/virtio_balloon.c | 19 +++++++++++++++++--
> 1 file changed, 17 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c
> index 9a61febbd2f7..7dc3fcd56238 100644
> --- a/drivers/virtio/virtio_balloon.c
> +++ b/drivers/virtio/virtio_balloon.c
> @@ -597,8 +597,23 @@ static int init_vqs(struct virtio_balloon *vb)
>
> err = virtio_find_vqs(vb->vdev, VIRTIO_BALLOON_VQ_MAX, vqs,
> callbacks, names, NULL);
> - if (err)
> - return err;
> + if (err) {
> + /*
> + * Try to work around QEMU bug which since 2020 confused vq numbers
> + * when VIRTIO_BALLOON_F_REPORTING but not
> + * VIRTIO_BALLOON_F_FREE_PAGE_HINT are offered.
> + */
> + if (virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_REPORTING) &&
> + !virtio_has_feature(vb->vdev, VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
> + names[VIRTIO_BALLOON_VQ_FREE_PAGE] = "reporting_vq";
> + callbacks[VIRTIO_BALLOON_VQ_FREE_PAGE] = balloon_ack;
> + err = virtio_find_vqs(vb->vdev,
> + VIRTIO_BALLOON_VQ_REPORTING, vqs, callbacks, names, NULL);
> + }
> +
> + if (err)
> + return err;
> + }
>
> vb->inflate_vq = vqs[VIRTIO_BALLOON_VQ_INFLATE];
> vb->deflate_vq = vqs[VIRTIO_BALLOON_VQ_DEFLATE];
> --
> MST
>
Acked-by: Jason Wang <jasowang@xxxxxxxxxx>
Do we need a spec to say this is something that needs to be considered
by the driver?
Thanks
