Kernel Debugging (KDNET)

Kernel Debugging is available for Windows guests via KDNET over VMBus.

Enabling and Starting the Debugger

Set up KDNET on the guest and start the debugger as described on Set up KDNET network kernel debugging manually | Microsoft Learn. Setting busparams is not necessary.

With OpenVMM and WHP as Host

Set up the VM for UEFI and VMBus depending on your use case and pass the additional flag --net consomme:

• Without OpenHCL: Pass the --uefi flags when starting OpenVMM.
• With OpenHCL: Ensure "UEFI Boot" and "VTL2 VMBus Support" are active

Known Issues with KDNET on WHP

• KDNET currently only works with the consomme networking option in OpenVMM, however consomme will create a new network adapter in the guest every time OpenVMM is restarted. This can be safely ignored.
  • KDNET will also connect with --net vmnic:<ethernet switch id>, but hangs immediately after due to a yet undiagnosed bug in vmbusproxy.
• Quitting OpenVMM without shutting down the VM first will prevent the same debugger instance from reconnecting to the guest on next boot. Relauch the debugger to reconnect.
• When launching an OpenHCL VM with KDNET, virt_whp::synic will report a constant stream of failed to signal synic errors for several seconds. These don't appear to affect the VM's functionality and can be ignored.