VirtualKD on Windows 8
VirtualKD 2.7 and later supports Windows 8 targets.
However, Windows 8 does not normally allow custom debug transport DLLs that are not signed by Microsoft (even a valid AuthentiCode signature is not sufficient).
There are 2 workarounds to this problem:
Every time your VM boots and you get an OS selection prompt (vminstall.exe will enable it), press F8:Then select "Disable driver signature enforcement":
You can avoid doing it every time. Just boot your VM with no driver signature enforcement once (just after you select Disabel Driver Signature Enforcement and press ENTER, run vmmon/vmmon64 on the host machine and, select your VM and start WinDbg; otherwise, Windows will boot without debugging support).
When your VM starts with WinDbg attached to it, create a snapshot. Later, simply restore the snapshot and re-attach WinDbg/VisualDDK to start debugging your driver immediately.