Hi Daniel and Michael, Thanks for the quick feedback.
Given the migration concerns and issues with the spec itself, I think it’ll be best to drop the code changes for now. Thanks again for the guidance, Aaron > On Dec 11, 2025, at 8:22 AM, Daniel P. Berrangé <[email protected]> wrote: > > On Thu, Dec 11, 2025 at 03:05:49AM -0600, Aaron Lo wrote: >> The VirtIO specification (section 5.5.2) states that the stats queue >> is only present if the VIRTIO_BALLOON_F_STATS_VQ feature is >> negotiated. QEMU currently creates the statsq unconditionally. >> >> This patch guards statsq creation so it occurs only when the >> feature bit is enabled. >> >> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/3188 >> >> Signed-off-by: Aaron Lo <[email protected]> >> --- >> hw/virtio/virtio-balloon.c | 9 +++++++-- >> 1 file changed, 7 insertions(+), 2 deletions(-) >> >> diff --git a/hw/virtio/virtio-balloon.c b/hw/virtio/virtio-balloon.c >> index 02cdd807d7..f5d4d5f60c 100644 >> --- a/hw/virtio/virtio-balloon.c >> +++ b/hw/virtio/virtio-balloon.c >> @@ -892,7 +892,10 @@ static void virtio_balloon_device_realize(DeviceState >> *dev, Error **errp) >> >> 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); >> + >> + if (virtio_has_feature(s->host_features, VIRTIO_BALLOON_F_STATS_VQ)) { >> + s->svq = virtio_add_queue(vdev, 128, virtio_balloon_receive_stats); >> + } > > This seems like a change that is liable to break live migration > state compatibility, as IIUC the queues are encoded in the state ? > >> >> if (virtio_has_feature(s->host_features, >> VIRTIO_BALLOON_F_FREE_PAGE_HINT)) { >> s->free_page_vq = virtio_add_queue(vdev, VIRTQUEUE_MAX_SIZE, >> @@ -932,7 +935,9 @@ static void virtio_balloon_device_unrealize(DeviceState >> *dev) >> >> virtio_delete_queue(s->ivq); >> virtio_delete_queue(s->dvq); >> - virtio_delete_queue(s->svq); >> + if (s->svq) { >> + virtio_delete_queue(s->svq); >> + } >> if (s->free_page_vq) { >> virtio_delete_queue(s->free_page_vq); >> } >> >> --- >> base-commit: 9c23f2a7b0b45277693a14074b1aaa827eecdb92 >> change-id: 20251211-balloon-check-stats-feature-7ea658e038ce >> >> Best regards, >> -- >> Aaron Lo <[email protected]> >> >> > > With regards, > Daniel > -- > |: https://berrange.com <https://berrange.com/> -o- > https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org <https://libvirt.org/> -o- > https://fstop138.berrange.com <https://fstop138.berrange.com/> :| > |: https://entangle-photo.org <https://entangle-photo.org/> -o- > https://www.instagram.com/dberrange :|
