We’ve identified an issue that happens sometimes in the nested virtualization environment and RT kernel (it has not been reproduced in other environments).

Sometimes the VM comes up and, although it can transmit packets, it cannot receive packets.

From the guest PoV, you can clearly see that port statistics show 0 received packets.

In the host, OVS logs show:

2025-08-12T08:28:43.614Z|00169|netdev_dpdk(ovs_vhost3)|INFO|State of queue 0 ( tx_qid 0 ) of vhost device '/dev/vduse/vduse18' changed to 'disabled'
2025-08-12T08:28:43.614Z|00170|netdev_dpdk(ovs_vhost3)|INFO|State of queue 1 ( rx_qid 0 ) of vhost device '/dev/vduse/vduse18' changed to 'enabled'

Note "disabled" in tx queue (RX from the guest’s perspective).

In such cases restarting OVS typically restores the traffic.

 Impact Assessment: Describe the severity and impact (e.g., network down,availability of a workaround, etc.).

Network down

 Software Versions: Specify the exact versions in use (e.g.,openvswitch3.1-3.1.0-147.el8fdp).

PoC of VDUSE and Kubevirt
OCP 4.19.0-0.nightly-2025-08-05-174154
kernel 5.14.0-570.32.1.el9_6.x86_64+rt
openvswitch3.5-3.5.1-44.el9.vduse.1.x86_64
Kubevirt HyperConverged 4.19.1

  Issue Type: Indicate whether this is a new issue or a regression (if a regression, state the last known working version).

New issue in feature in active development

 Reproducibility: Confirm if the issue can be reproduced consistently. If not, describe how often it occurs.

I'd say around 33% of the times I spin up a VM

 Reproduction Steps: Provide detailed steps or scripts to replicate the issue.

https://docs.google.com/document/d/1nEP3dt3Kssh-7rVl3yEvBQtixY0pYRAyj4R78w-7aR8/edit?tab=t.0

 Expected Behavior: Describe what should happen under normal circumstances.

VM should have connectivity both rx and tx

 Observed Behavior: Explain what actually happens.

VM only has tx connectivity, no rx.

 Troubleshooting Actions: Outline the steps taken to diagnose or resolve the issue so far.

Restarting OVS seems to re-establish connectivity

 Logs: If you collected logs please provide them (e.g. sos report, /var/log/openvswitch/* , testpmd console)