I'm not sure about xhyve, but I vaguely remember Hyper-V supports nested virtualization but only on Windows guests. Something Microsoft seems to need that for the upcoming Windows containers.

Your best option for nested virtualization seems to be qemu, but you don't need virtualization for Docker on Linux so it's pointless.

VirtualBox doesn't support nested virtualization either.

Absolutely, I too would really like this, especially if you could easily do PCIe / Thunderbolt passthrough for GPUs.

Curious, can you share what you need it for?

Basically for hacking on cloud software that runs hypervisors such as kvm. docker-machine with a VMWare Fusion VM and nested virtualization enabled is the current approach I use - works fine for now.

Looks like you need nested virtualization for running windows xp apps within the new newer windows systems.

I'm also curious about other uses for it. Why is it a must have when you could technically just use a virtual windows xp system. I guess running a legacy application in a more secure and newer OS?