Re: [Qemu-devel] [PATCH 2/2] virtio-rng: stop virtqueue while the CPU is stopped

[Stefan Hajnoczi <stefanha@redhat.com>]

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On Tue, Apr 11, 2017 at 03:17:33PM +0200, Laurent Vivier wrote:
> diff --git a/hw/virtio/virtio-rng.c b/hw/virtio/virtio-rng.c
> index 9639f4e..d270d56 100644
> --- a/hw/virtio/virtio-rng.c
> +++ b/hw/virtio/virtio-rng.c
> @@ -53,6 +53,15 @@ static void chr_read(void *opaque, const void *buf, size_t size)
>          return;
>      }
>  
> +    /* we can't modify the virtqueue until
> +     * our state is fully synced
> +     */
> +
> +    if (!runstate_check(RUN_STATE_RUNNING)) {
> +        trace_virtio_rng_cpu_is_stopped(vrng);
> +        return;
> +    }
> +

I'm concerned about what happens when the guest is stopped and resumed
(e.g. 'stop' and 'cont' monitor commands).  Since we throw away the
chr_read() callback the device will hang unless the guest kicks it
again?

It's not clear to me that the rate limit timer will help us...

Stefan

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