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Comment by damnyou | Hacker News Reader

Don't all hypervisors disable other hypervisors?

No. It's a fairly common use case to i.e. virtualize several ESXi hypervisors underneath ESXi itself, in order to test clusters or other setups. VMWare calls the feature VHV, "virtual hardware-assisted virtualization". More generally, it's typically just "nested virtualization". It does look like it needs some CPU features, but which are now old enough to be essentially commodity.

(and yes, ESXi is a type 1 hypervisor--it's definitely something Microsoft could enable more broadly, instead of limiting the scope to Hyper-V nested setups)

Is it possible to run other hypervisors under Hyper-V as well? What about next to ESXi (as opposed to underneath it)?

I'm learning a lot from this conversation, thanks.

You are either in or under, not side by side. Yes, it is possible to run a hypervisor in a hypervisor, the limitation is usually in the parent hypervisor. In this particular case it would be useful to run side by side, but it is not possible and it also negates the idea of multiple hypervisors: why not have a single one running all the VM's?

You can run Hyper-V inside Hyper-V on Intel CPUs, but, not on AMD EPYC/Ryzen yet.

(Not sure about nesting other hypervisors.)

While running, yes. On Windows if you enable Hyper-V support, even when you're not using it at the moment, you can't use VirtualBox without reboots and shit.

This is because Hyper-V is a level 1 hypervisor (similar to Xen) while VirtualBox is a level 2 (similar to QEMU). Hyper-V is always running because the Windows "host" OS is actually running under it's control as well.

> Hyper-V is always running because the Windows "host" OS is actually running under it's control as well.

Wait really? That doesn't seem right, why would they have the host running under part of hyper v when hyper v is optional? This would mean the entire foundation shifts when you enable or disable hyper v

Hence the reboots.

Yeah, that's why the reboot is required, it's like changing kernels on linux. I think they are moving to have it on by default, and eventually they may just make it permanently part of the OS install. Kind of like how they take control of the TPM on install even if you don't setup BitLocker, I imagine they will just have the core hypervisor permanently enabled and then it's up to the user setting what actually uses its features.

This system has resulted in issues in the "host" and with an unresponsive control plane for me the few times I've tried to use it. Compared to no issues with type 2s.

To say nothing of the madness of using it on a laptop with several network adapters when the guest OS only wants to acknowledge one.

Hypervisor Framework and VirtualBox seem to cohabit just fine on MacOS.

https://www.virtualbox.org/ticket/14217 seems to indicate not so much unless VirtualBox has switched to using it as a backend.

That ticket is just a wishlist request — there's no indication of a problem there.

Yeah. VirtualBox installs its own kernel extension at this point in time.

But can you run VBox and (say) Docker at the same time?

Yep. I ran docker and Fusion at the same time and it works great.

No.

I concurrently build vagrant boxes (using Packer) for VirtualBox, VMWare and Parallels on macOS.

All of those are level 2 hypervisors. Hyper V is a level 1 hypervisor.

My point is that it's fundamental to the way the tech works.

Great, but that's a design decision Microsoft made when implementing a solution for desktops and workstations.

Sure, a level 1 HV makes a lot of sense for a VM host.

For this, not so much.

It is a VM host: when Hyper-V is active, Windows itself is just another VM. (That's why you have to reboot when you turn Hyper-V on or off). NT isn't actually privileged compared to the Linux kernel in WSL2!

Most likely in the next few years Hyper-V will become non-optional and Windows will always be virtualized when you run it. That's a big architectural shift that will enable lots of cool new scenarios, but it requires a level 1 hypervisor.

One interesting rumor that has been around for years is that Xbox games could always start requiring Hyper-V on Windows. On an Xbox One, Hyper-V is already in charge and games (mostly) run in extremely lightweight VMs. Supposedly there is interest in bringing those game VMs directly to Windows for power-user game performance.

When I said “vm host” I meant a server in a rack.

But sure, keep down voting because someone said your dumpster fire OS is crap.

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