Re: Nested virtualization on Intel does not work - second level freezes when third level is starting

[Guido Winkelmann <guido-kvml@thisisnotatest.de>]

Am Mittwoch, 11. April 2012, 17:38:14 schrieb Nadav Har'El:
> On Wed, Apr 11, 2012, Guido Winkelmann wrote about "Nested virtualization on 
> Intel does not work - second level freezes when third level is starting":
> > Nested virtualization on Intel does not work for me with qemu-kvm. As soon
> > as the third layer OS (second virtualised) is starting the Linux kernel,
> > the entire second layer freezes up. The last thing I can see console of
> > the third
> Hi,
> 
> From your description, I understand that "ordinary" (2-level) nested
> virtualization working for you (host, guest and 2nd-level guest), and it's
> the third nesting level (guest's guest's guest) which is broken?

No, even 2-level nesting is broken. I can run Host->Guest, but not 
Host->Guest->2nd Level Guest. I haven't even tried with a third virtualized 
level.

I suppose the misunderstanding happened because, in my original mail, I was 
counting the host as one level.

> This is the second report of this nature in a week (see the previous
> report in https://bugzilla.kernel.org/show_bug.cgi?id=43068 - the
> details there are different), so I guess I'll need to find the time
> to give this issue some attention. L3 did work for me when the nested
> VMX patches were included in KVM, so either something broke since, or
> (perhaps more likely) your slightly different setups have features that
> my setup didn't.
> 
> But in any case, like I explain in the aforementioned URL, even if L3 would
> work, in the current implementation it would be extremenly slow - perhaps to
> the point of being unusable (I think you saw this with grub performance in
> L3). So I wonder if you'd really want to use it, even if it worked... Just
> curious, what were you thinking of doing with L3?

I was trying to test network setups that involve migrating VMs between hosts a 
lot, and I was hoping to be able to use only one physical server for that.

As I said, I really only need one level of nesting for that (i.e. two levels 
of virtualization, three levels of OSes when counting the host).

	Guido