On Thu, 19 May 2011 09:10:32 +0100, Invisible wrote:

>>>> Actually, it isn't - virtualizing virtualization solutions doesn't
>>>> tend to work very well at all.
>>>
>>> QEMU doesn't use hardware virtualisation. It does software emulation
>>> only. This is why it's trivial to do what I described.
>>
>> Even for software-based virtualization (emulation is different), it
>> wouldn't work so well, to the best of my knowledge.
> 
> My understanding is that QEMU does full software emulation of the guest
> system. (It can even emulate an architecture different than the one it's
> running on.) Assuming it emulates the full capabilities of the guest, I
> don't see why you can't run QEMU inside QEMU.

It's not trival to emulate an emulation system under emulation.  Just 
like it isn't trivial to virtualize a virtualization system in a virtual 
environment.   Trust me, I've worked with this stuff quite a lot.

QEMU doesn't emulate the guest OS, just the hardware.  That's the essence 
of virtualization.

> If it's using the host hardware to accelerate things, then that of
> course is a different matter. Generally the scheme only supports one
> layer of virtualisation, not two.

That's not really what hardware virtualization does.  It essentially 
creates a separate Ring0 space within the hardware to run things at full 
hardware speed.

>>> For stuff that uses real hardware virtualisation... yeah, that tends
>>> not to work. Although I have successfully run VirtualBox inside VMware
>>> Workstation. (Had to tweak some options though, turning off some of
>>> the hardware acceleration...)
>>
>> It can be done, sure; it's not very stable.
> 
> I'm sure it's not a very "supported" route, but I managed to get Windows
> XP running inside Windows XP (running inside Windows XP). I only
> actually wanted to see what VirtualBox is like, without installing it
> for real. (Isn't that the point of desktop virtualisation? To test
> things without "really" installing them?) I wouldn't recommend using
> such a configuration "for real", no.

Yes, it's been *done*, but it's not particularly *stable*.  For my own 
purposes, I needed an environment that was stable enough to be reliable 
for testing people's skills on virtualization technologies.  Even the SMEs 
that I talked to about it said "you're nuts because it just isn't stable 
to do so".

Jim

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