virtualbox - Why can't I create a 64-bit virtual machine inside another virtual machine?

Question

I am trying to create a new 64-bit Windows 7 virtual machine inside a 64-bit Debian 7.3.0 instance running in VirtualBox. I am allowed to run 32-bit machines, but I can not create 64-bit machines, as shown in the picture. Why is this? I have hardware virtualization enabled on the host.

Solution

I read this... "You must enable hardware virtualization for the particular VM for which you want 64-bit support; software virtualization is not supported for 64-bit VMs"

I am guessing since virtualbox is software, it will not support a 64-bit OS running from a 64-bit OS VM. That is my theory, maybe post system specs and what exactly is happening when you go to create another VM inside your VM.

Comments

[Daniel R Hicks]

Maybe because it's not turtles all the way down.

[hmijail mourns resignees]

The linked-as-duplicate question is not a duplicate, since that one was about Bochs (pure software) over any VM, and this question is specifically about VirtualBox on VirtualBox. Fortunately there are some useful answers there. Summary: it just has not been implemented (yet?): see virtualbox.org/ticket/4032. FWIW, VMWare does support nested VMs.

[user1049697]

It's true that it is a bit of an odd setup. :) But I need to run some Linux software that again needs a virtual machine to work with, hence the machines inside the machines.

[Julian Knight]

Fair enough - thought it might be something like that. You will have to live with 32bit and rubbish performance though I'm afraid.

[David Schwartz]

Bingo. A VM cannot provide hardware virtualization support since it isn't hardware.

[Robin Hood]

@user1049697 "run some Linux software that again needs a virtual machine to work with" You realize VB can have more than 1 virtual machine on the host, even at the same time.

[Daniel R Hicks]

But there's no reason why hardware virtualization can't be simulated (other that, of course, performance, code size, memory, et al).

[konqui]

as Robin mentioned i would also use to vm's in the same host rather than a vm inside a vm. - the performance of the vm inside the vm earlier or later will drive you crazy

[Matt Stevens]

Not such an odd set-up, we are using VMs to get around not having super user privileges on University machines.

[Julian Knight]

@MattStevens Perhaps if you raise a question describing what you are trying to achieve, someone might come up with a less odd solution. I can think of several but it depends on what you are trying to do with that double-embedded VM.