[vbox-dev] Nested virtualization problem

[Klaus Espenlaub]

On 13.10.2010 21:35, Geoff Nordli wrote:
>> -----Original Message-----
>> From: Ruben Van den Bossche
>> Sent: Monday, October 11, 2010 1:59 AM
>>
>>   Dear VBox developers,
>>
>> We are currently extending work performed by Olivier Berghmans regarding
>> nested virtualization (running a virtual machine inside another virtual
> machine).
>> Because none of us has experience with hypervisor development, we would
> very
>> much appreciate it if you could confirm or correct one of our assumptions.
>>
>> In our experiments, nesting DBT based hypervisors appears impossible when
> using
>> a base hypervisor based on DBT. Using first generation hardware support as
> the
>> base hypervisor results in partial success depending on the hypervisor used
> (
>> VMWare, Xen, KVM, Virtualbox ). When we move the base hypervisor to a
>> machine with second generation hardware support most problems disappear.
>>
>> We think the most likely reason for the problems with DBT or first gen.
>> hardware support as base hypervisor technique are the results of shadow
> paging,
>> and more specifically the nested shadow paging which occurs when nesting
> DBT
>> on DBT or first gen HWS. Perhaps some functionality is not replicated
> exactly as
>> one would expect on physical hardware?  Maybe some shortcuts result in
> corrupt
>> memory if they are used in nested hypervisors? If you could confirm these
>> assumptions or perhaps even give some greater insight in these problems, we
>> would be extremely grateful.
>>
>> Kind Regards,
>>
>> Sam Verboven and Ruben Van den Bossche
>> PhD Students
>> University of Antwerp
>
> Being able to do nested virtualization would be an amazing feature in
> VirtualBox!!!!

Not sure if you're aware that such "amazing" statements tend to 
discredit the message you're trying to bring across. There are so many 
features VirtualBox could have, and for some reason this word is only 
used in a context where there is most likely near zero customer demand 
for something which requires weeks of work for the most skilled engineers.

That said, of course it would be an amazing feature ;)

> We are in the training field, and if we could run hypervisor related
> training like VMWare and Hyper-V on vbox that would be an outrageously
> amazing feature.

What I know is that one can run VirtualBox (in software virtualization 
mode) in a VirtualBox VM in hardware virtualization mode. The same 
should work for other virtualizers, although I personally haven't tried.

Klaus


> In addition some software like the new Windows Phone 7 software emulator
> uses virtualization.
>
> Geoff