Re: [PATCH] virtio: Call set_features during reset

[Akihiko Odaki]

On 2025/04/10 16:48, 'Michael S. Tsirkin' via devel wrote:
On Thu, Apr 10, 2025 at 04:42:06PM +0900, Akihiko Odaki wrote:
virtio-net expects set_features() will be called when the feature set
used by the guest changes to update the number of virtqueues. Call it
during reset as reset clears all features and the queues added for
VIRTIO_NET_F_MQ or VIRTIO_NET_F_RSS will need to be removed.
Fixes: f9d6dbf0bf6e ("virtio-net: remove virtio queues if the guest doesn't support 
multiqueue")
Buglink: https://issues.redhat.com/browse/RHEL-73842
Cc: qemu-sta...@nongnu.org
Signed-off-by: Akihiko Odaki <akihiko.od...@daynix.com>

The issue seems specific to virtio net: rset is reset,
it is distict from set features.
Why not just call the necessary functionality from virtio_net_reset?

set_features is currently implemented only in virtio-net; 
virtio-gpu-base also have a function set but it only has code to trace. 
If another device implements the function in the future, I think the 
device will also want to have it called during reset for the same reason 
with virtio-net.

virtio_reset() also calls set_status to update the status field so 
calling set_features() is more aligned with the handling of the status 
field.



---
  hw/virtio/virtio.c | 86 +++++++++++++++++++++++++++---------------------------
  1 file changed, 43 insertions(+), 43 deletions(-)

diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 85110bce3744..033e87cdd3b9 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2316,49 +2316,6 @@ void virtio_queue_enable(VirtIODevice *vdev, uint32_t 
queue_index)
      }
  }
  
-void virtio_reset(void *opaque)
-{
-    VirtIODevice *vdev = opaque;
-    VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
-    int i;
-
-    virtio_set_status(vdev, 0);
-    if (current_cpu) {
-        /* Guest initiated reset */
-        vdev->device_endian = virtio_current_cpu_endian();
-    } else {
-        /* System reset */
-        vdev->device_endian = virtio_default_endian();
-    }
-
-    if (k->get_vhost) {
-        struct vhost_dev *hdev = k->get_vhost(vdev);
-        /* Only reset when vhost back-end is connected */
-        if (hdev && hdev->vhost_ops) {
-            vhost_reset_device(hdev);
-        }
-    }
-
-    if (k->reset) {
-        k->reset(vdev);
-    }
-
-    vdev->start_on_kick = false;
-    vdev->started = false;
-    vdev->broken = false;
-    vdev->guest_features = 0;
-    vdev->queue_sel = 0;
-    vdev->status = 0;
-    vdev->disabled = false;
-    qatomic_set(&vdev->isr, 0);
-    vdev->config_vector = VIRTIO_NO_VECTOR;
-    virtio_notify_vector(vdev, vdev->config_vector);
-
-    for(i = 0; i < VIRTIO_QUEUE_MAX; i++) {
-        __virtio_queue_reset(vdev, i);
-    }
-}
-
  void virtio_queue_set_addr(VirtIODevice *vdev, int n, hwaddr addr)
  {
      if (!vdev->vq[n].vring.num) {
@@ -3169,6 +3126,49 @@ int virtio_set_features(VirtIODevice *vdev, uint64_t val)
      return ret;
  }
  
+void virtio_reset(void *opaque)
+{
+    VirtIODevice *vdev = opaque;
+    VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(vdev);
+    int i;
+
+    virtio_set_status(vdev, 0);
+    if (current_cpu) {
+        /* Guest initiated reset */
+        vdev->device_endian = virtio_current_cpu_endian();
+    } else {
+        /* System reset */
+        vdev->device_endian = virtio_default_endian();
+    }
+
+    if (k->get_vhost) {
+        struct vhost_dev *hdev = k->get_vhost(vdev);
+        /* Only reset when vhost back-end is connected */
+        if (hdev && hdev->vhost_ops) {
+            vhost_reset_device(hdev);
+        }
+    }
+
+    if (k->reset) {
+        k->reset(vdev);
+    }
+
+    vdev->start_on_kick = false;
+    vdev->started = false;
+    vdev->broken = false;
+    virtio_set_features_nocheck(vdev, 0);
+    vdev->queue_sel = 0;
+    vdev->status = 0;
+    vdev->disabled = false;
+    qatomic_set(&vdev->isr, 0);
+    vdev->config_vector = VIRTIO_NO_VECTOR;
+    virtio_notify_vector(vdev, vdev->config_vector);
+
+    for (i = 0; i < VIRTIO_QUEUE_MAX; i++) {
+        __virtio_queue_reset(vdev, i);
+    }
+}
+
  static void virtio_device_check_notification_compatibility(VirtIODevice *vdev,
                                                             Error **errp)
  {

---
base-commit: 825b96dbcee23d134b691fc75618b59c5f53da32
change-id: 20250406-reset-5ed5248ee3c1

Best regards,
--
Akihiko Odaki <akihiko.od...@daynix.com>