Re: [Qemu-devel] [PATCH] virtio_rpmsg: set DRIVER_OK before using device

[Rusty Russell]

"Michael S. Tsirkin" <address@hidden> writes:
> virtio spec requires that all drivers set DRIVER_OK
> before using devices. While rpmsg isn't yet
> included in the virtio 1 spec, previous spec versions
> also required this.
>
> virtio rpmsg violates this rule: is calls kick
> before setting DRIVER_OK.
>
> The fix isn't trivial since simply calling virtio_device_ready earlier
> would mean we might get an interrupt in parallel with adding buffers.
>
> Instead, split kick out to prepare+notify calls.  prepare before
> virtio_device_ready - when we know we won't get interrupts. notify right
> afterwards.
>
> Signed-off-by: Michael S. Tsirkin <address@hidden>

Applied.  I'll wait for Ohad to ack before sending to Linus.

BTW I assume you have a version of qemu which warns on these kind of
failures?  That'd be nice to have!

Thanks,
Rusty.

> ---
>
> Note: compile-tested only.
>
>  drivers/rpmsg/virtio_rpmsg_bus.c | 17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/rpmsg/virtio_rpmsg_bus.c 
> b/drivers/rpmsg/virtio_rpmsg_bus.c
> index 92f6af6..73354ee 100644
> --- a/drivers/rpmsg/virtio_rpmsg_bus.c
> +++ b/drivers/rpmsg/virtio_rpmsg_bus.c
> @@ -951,6 +951,7 @@ static int rpmsg_probe(struct virtio_device *vdev)
>       void *bufs_va;
>       int err = 0, i;
>       size_t total_buf_space;
> +     bool notify;
>  
>       vrp = kzalloc(sizeof(*vrp), GFP_KERNEL);
>       if (!vrp)
> @@ -1030,8 +1031,22 @@ static int rpmsg_probe(struct virtio_device *vdev)
>               }
>       }
>  
> +     /*
> +      * Prepare to kick but don't notify yet - we can't do this before
> +      * device is ready.
> +      */
> +     notify = virtqueue_kick_prepare(vrp->rvq);
> +
> +     /* From this point on, we can notify and get callbacks. */
> +     virtio_device_ready(vdev);
> +
>       /* tell the remote processor it can start sending messages */
> -     virtqueue_kick(vrp->rvq);
> +     /*
> +      * this might be concurrent with callbacks, but we are only
> +      * doing notify, not a full kick here, so that's ok.
> +      */
> +     if (notify)
> +             virtqueue_notify(vrp->rvq);
>  
>       dev_info(&vdev->dev, "rpmsg host is online\n");
>  
> -- 
> MST