A case that Hyper-V freezes host operating system

Two days ago I set up a new virtual machine for applications that require isolated security. When I put my computer into Connected Standby mode, I noticed SoC fan didn’t stop. To verify whether it was OS inconsistency or persistent issue, I manually initiated a system restart. However, it froze at login screen then. Nothing responded, including Ctrl + Alt + Delete key sequence. Attempting to force shutdown and start the computer almost didn’t improve the situation. After about ten attempts I managed to enter my desktop. There was no clue in event viewer: everything went well then suddenly the system froze.

I remembered that an alternative OS loader entry was configured to bypass Hypervisor launch at startup. I selected this entry to see whether it was related to Hyper-V. Test results indicated the freeze issue was strongly related to Hyper-V.

I tried to remember what I did before virtual machine configuration. I removed a virtual switch bridged to Surface Ethernet Adapter on my Surface Dock, then added a virtual switch bridged to VMware NAT adapter (which works better with Wireless network). Then I checked adapters in Network and Sharing Center, the old virtual switch didn’t get removed at all – and the “Remove” menu entry was unavailable. At last, I removed this adapter from Device Manager, and the issue was resolved.

This issue is likely related to OS inconsistency. When Hyper-V infrastructure attempts to initialize (bring up) all enabled network adapters including these Hyper-V virtual switches, the “removed” adapter is brought up, then enters failure state due to inconsistency in configuration. Because host operating system is a virtual machine on Hyper-V (with privileges), the host OS didn’t even get a chance to record what happened at that point.

The good thing is that I fixed it by myself; The bad thing is I missed an opportunity to report this bug and let Microsoft fix it.