Re: Nested VMX support - kernel v1

[Muli Ben-Yehuda <muli@il.ibm.com>]

On Wed, Sep 02, 2009 at 05:57:39PM +0200, Alexander Graf wrote:
>
> Am 02.09.2009 um 17:38 schrieb oritw@il.ibm.com:
>
>> The following patches implement nested VMX support. The patches
>> enable a guest to use the VMX APIs in order to run its own nested
>> guest (i.e., enable running other hypervisors which use VMX under
>> KVM).
>
> Copl! Great job here. I was expecting vmcs load/stores to kill
> performance, but apparently I was wrong. How did you get those fast?

Are you asking about vmptrld (switching the VMCS's) or the costs of
trapping vmread/vmwrites?

>> The current patches support running Linux under a nested KVM using
>> shadow page table (with bypass_guest_pf disabled).
>
> What is keeping you from running the other hypervisors, guests?

A simple matter of programming (or more accurately, debugging). There
are no fundamental limitations that preclude running other hypervisors
or multiple guests, but we've been concentrating on getting a single
hypervisor (both KVM and VMware) performing well first.

>> SMP support was fixed.  Reworking EPT support to mesh cleanly with
>> the current shadow paging design per Avi's comments is a
>> work-in-progress.
>>
>> The current patches only support a single nested hypervisor
>
> Why?

See above---no fundamental limitation---but needs more work. Bug
reports happily accepted, patches even more so :-)

>> , which can only run a single guest (multiple guests are work in
>> progress). Only 64-bit nested hypervisors are supported.
>>
>> Additional patches for running Windows under nested KVM, and Linux
>> under nested VMware server(!),
>
> GSX or ESX? With ESX I was running into TSC timing issues because
> ESX didn't like the fact it got preempted :-).

GSX. I expect the issues you've run into are not SVM specific, so
likely they'll need to be address for VMX as well.

> How about Hyper-V and Xen?

We haven't tried them.

> Again, great job and congratulations on making this work!

Thank you, your patches were very useful!

Cheers,
Muli
-- 
Muli Ben-Yehuda | muli@il.ibm.com | +972-4-8281080
Manager, Virtualization and Systems Architecture
Master Inventor, IBM Haifa Research Laboratory