On Fri, Aug 05, 2016 at 01:36:32PM +0200, Ladi Prosek wrote:
> The stats_vq_elem field keeps track of the state of the balloon stats
> virtqueue protocol but it wasn't preserved across migrations, resulting
> in losing guest memory status updates on the receiving VM.
>
> This commit adds a new VM state change handler which resets stats_vq_elem
> to NULL when the VM is stopped, eliminating the need for the field to be
> migrated. When the VM starts running again, the field is reinitialized by
> re-popping the element from the virtqueue.
>
> Signed-off-by: Ladi Prosek <lpro...@redhat.com>
> Suggested-by: Michael S. Tsirkin <m...@redhat.com>
Almost there. Except we should not touch rings
unless guest set DRIVER_OK in status register, and we should
not touch status vq at all unless VIRTIO_BALLOON_F_STATS_VQ
has been negotiated.
I'll post a patch to do this.
> ---
> hw/virtio/virtio-balloon.c | 23 +++++++++++++++++++++++
> include/hw/virtio/virtio-balloon.h | 1 +
> 2 files changed, 24 insertions(+)
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 5af429a..65457e9 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -423,6 +423,26 @@ static int virtio_balloon_load_device(VirtIODevice
> *vdev, QEMUFile *f,
> return 0;
> }
>
> +static void virtio_balloon_vmstate_cb(void *opaque, int running,
> + RunState state)
> +{
> + VirtIOBalloon *s = opaque;
> +
> + if (!running) {
> + /* put the stats element back if the VM is not running */
> + if (s->stats_vq_elem != NULL) {
> + virtqueue_discard(s->svq, s->stats_vq_elem, s->stats_vq_offset);
> + g_free(s->stats_vq_elem);
> + s->stats_vq_elem = NULL;
> + }
> +
> + } else {
> + /* poll stats queue for the element we may have discarded
> + * when the VM was stopped */
> + virtio_balloon_receive_stats(VIRTIO_DEVICE(s), s->svq);
> + }
> +}
> +
> static void virtio_balloon_device_realize(DeviceState *dev, Error **errp)
> {
> VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> @@ -446,6 +466,8 @@ static void virtio_balloon_device_realize(DeviceState
> *dev, Error **errp)
> s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
>
> reset_stats(s);
> +
> + s->change = qemu_add_vm_change_state_handler(virtio_balloon_vmstate_cb,
> s);
> }
>
> static void virtio_balloon_device_unrealize(DeviceState *dev, Error **errp)
> @@ -453,6 +475,7 @@ static void virtio_balloon_device_unrealize(DeviceState
> *dev, Error **errp)
> VirtIODevice *vdev = VIRTIO_DEVICE(dev);
> VirtIOBalloon *s = VIRTIO_BALLOON(dev);
>
> + qemu_del_vm_change_state_handler(s->change);
> balloon_stats_destroy_timer(s);
> qemu_remove_balloon_handler(s);
> virtio_cleanup(vdev);
> diff --git a/include/hw/virtio/virtio-balloon.h
> b/include/hw/virtio/virtio-balloon.h
> index 1ea13bd..d72ff7f 100644
> --- a/include/hw/virtio/virtio-balloon.h
> +++ b/include/hw/virtio/virtio-balloon.h
> @@ -43,6 +43,7 @@ typedef struct VirtIOBalloon {
> int64_t stats_last_update;
> int64_t stats_poll_interval;
> uint32_t host_features;
> + VMChangeStateEntry *change;
> } VirtIOBalloon;
>
> #endif
> --
> 2.5.5
