Re: [Qemu-devel] [PATCH-for-4.1 v2 3/3] virtio-balloon: reset pbp on device resets

[Michael S. Tsirkin]

On Wed, Jul 17, 2019 at 12:35:50PM +0200, David Hildenbrand wrote:
> When a guest reboots (ordinary reboots, but also via kexec), it will
> happily reuse any system memory, including previously inflated memory.
> 
> We could have tracking data for a pbp (PartiallyBalloonedPage). It could
> happen that a new inflation request from the guest will result in a
> discard of such a pbp, although the guest is (again) reusing some
> memory.
> 
> We should reset the pbp on any device resets.
> 
> Fixes: ed48c59875b6 ("virtio-balloon: Safely handle BALLOON_PAGE_SIZE <
>                      host page size")
> Cc: address@hidden #v4.0.0
> Cc: Stefan Hajnoczi <address@hidden>
> Cc: David Gibson <address@hidden>
> Cc: Michael S. Tsirkin <address@hidden>
> Cc: Igor Mammedov <address@hidden>
> Signed-off-by: David Hildenbrand <address@hidden>

Can't something else remove a ramblock besides a reset?


> ---
>  hw/virtio/virtio-balloon.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 84d01bceb3..9de3c030bf 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -847,6 +847,7 @@ static void virtio_balloon_device_reset(VirtIODevice 
> *vdev)
>      if (virtio_balloon_free_page_support(s)) {
>          virtio_balloon_free_page_stop(s);
>      }
> +    virtio_balloon_reset_pbp(s);
>  
>      if (s->stats_vq_elem != NULL) {
>          virtqueue_unpop(s->svq, s->stats_vq_elem, 0);
> -- 
> 2.21.0