Sorry to necropost, but I came across this same issue with my PVE host and thought that others may find this thread via google (as I did) and I wanted to add my 2c.
FOG kernel support or a custom kernel are probably the ideal solutions, but a quick and dirty workaround is to remove the Virtio vHDD from the VM and reload the .raw file as IDE. Everything then works as expected! 🙂