Re: [PATCH v1 1/3] virtio-balloon: fix free page hinting without an iothread

[Alexander Duyck]

On Mon, May 18, 2020 at 1:37 AM David Hildenbrand <address@hidden> wrote:
>
> In case we don't have an iothread, we mark the feature as abscent but
> still add the queue. 'free_page_bh' remains set to NULL.
>
> qemu-system-i386 \
>         -M microvm \
>         -nographic \
>         -device virtio-balloon-device,free-page-hint=true \
>         -nographic \
>         -display none \
>         -monitor none \
>         -serial none \
>         -qtest stdio
>
> Doing a "write 0xc0000e30 0x24
> 0x030000000300000003000000030000000300000003000000030000000300000003000000"
>
> We will trigger a SEGFAULT. Let's move the check and bail out.
>
> While at it, move the static initializations to instance_initialize().
>
> Fixes: c13c4153f76d ("virtio-balloon: VIRTIO_BALLOON_F_FREE_PAGE_HINT")
> Reported-by: Alexander Bulekov <address@hidden>
> Cc: Wei Wang <address@hidden>
> Cc: Michael S. Tsirkin <address@hidden>
> Cc: Philippe Mathieu-Daudé <address@hidden>
> Cc: Alexander Duyck <address@hidden>
> Signed-off-by: David Hildenbrand <address@hidden>
> ---
>  hw/virtio/virtio-balloon.c | 35 ++++++++++++++++++-----------------
>  1 file changed, 18 insertions(+), 17 deletions(-)
>
> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c
> index 065cd450f1..dc3b1067ab 100644
> --- a/hw/virtio/virtio-balloon.c
> +++ b/hw/virtio/virtio-balloon.c
> @@ -789,6 +789,13 @@ static void virtio_balloon_device_realize(DeviceState 
> *dev, Error **errp)
>          return;
>      }
>
> +    if (virtio_has_feature(s->host_features,
> +        VIRTIO_BALLOON_F_FREE_PAGE_HINT) && !s->iothread) {
> +        error_setg(errp, "'free-page-hint' requires 'iothread' to be set");
> +        virtio_cleanup(vdev);
> +        return;
> +    }
> +
>      s->ivq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>      s->dvq = virtio_add_queue(vdev, 128, virtio_balloon_handle_output);
>      s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats);
> @@ -797,24 +804,11 @@ static void virtio_balloon_device_realize(DeviceState 
> *dev, Error **errp)
>                             VIRTIO_BALLOON_F_FREE_PAGE_HINT)) {
>          s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE,
>                                             
> virtio_balloon_handle_free_page_vq);
> -        s->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
> -        s->free_page_report_cmd_id =
> -                           VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
> -        s->free_page_report_notify.notify =
> -                                       
> virtio_balloon_free_page_report_notify;
>          precopy_add_notifier(&s->free_page_report_notify);
> -        if (s->iothread) {
> -            object_ref(OBJECT(s->iothread));
> -            s->free_page_bh = 
> aio_bh_new(iothread_get_aio_context(s->iothread),
> -                                       virtio_ballloon_get_free_page_hints, 
> s);
> -            qemu_mutex_init(&s->free_page_lock);
> -            qemu_cond_init(&s->free_page_cond);
> -            s->block_iothread = false;
> -        } else {
> -            /* Simply disable this feature if the iothread wasn't created. */
> -            s->host_features &= ~(1 << VIRTIO_BALLOON_F_FREE_PAGE_HINT);
> -            virtio_error(vdev, "iothread is missing");
> -        }
> +
> +        object_ref(OBJECT(s->iothread));
> +        s->free_page_bh = aio_bh_new(iothread_get_aio_context(s->iothread),
> +                                     virtio_ballloon_get_free_page_hints, s);
>      }
>      reset_stats(s);
>  }
> @@ -892,6 +886,13 @@ static void virtio_balloon_instance_init(Object *obj)
>  {
>      VirtIOBalloon *s = VIRTIO_BALLOON(obj);
>
> +    qemu_mutex_init(&s->free_page_lock);
> +    qemu_cond_init(&s->free_page_cond);
> +    s->free_page_report_status = FREE_PAGE_REPORT_S_STOP;
> +    s->free_page_report_cmd_id = VIRTIO_BALLOON_FREE_PAGE_REPORT_CMD_ID_MIN;
> +    s->free_page_report_notify.notify = 
> virtio_balloon_free_page_report_notify;
> +    s->block_iothread = false;
> +
>      object_property_add(obj, "guest-stats", "guest statistics",
>                          balloon_stats_get_all, NULL, NULL, s);
>

So the one nit I have is that I am not sure you need to bother with
initializing block_iothread since it should already be initialized to
false/0 shouldn't it? Otherwise this all looks good to me.

Reviewed-by: Alexander Duyck <address@hidden>