[PATCH] virtio-balloon: only create statsq when VIRTIO_BALLOON_F_STATS_VQ exists

[Aaron Lo <aaronlo0929@gmail.com>]

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 <aaronlo0929@gmail.com>
---
 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);
+    }
 
     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 <aaronlo0929@gmail.com>