what's the type of nested xen? HVM or PV?

what's the type of nested xen? HVM or PV?

[quizyjones]

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Happy Holiday, guys. God tell me that I should work this out before celebrate ; )I create a HVM first, then compile Xen on it. The dom0 of this Xen is a PV. So is this nested xen a HVM or a PV? It's hard to differentiate when concerning to enable events as only HVM supports events. 		 	   		  

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Re: what's the type of nested xen? HVM or PV?

[Stefano Stabellini]

On Thu, 24 Dec 2015, quizyjones wrote:
> Happy Holiday, guys. God tell me that I should work this out before celebrate ; )I create a HVM first, then
> compile Xen on it. The dom0 of this Xen is a PV. So is this nested xen a HVM or a PV? It's hard to differentiate
> when concerning to enable events as only HVM supports events.

Xen itself, the hypervisor, is neither HVM or PV. HVM and PV are types
of virtual machines; the distinction doesn't apply to the hypervisor.

Dom0 is always PV (unless you use PVH which is experimental and not
something you would use by chance).

All the other nested guests are going to be PV unless you passed
nestedhvm=1 in your external VM config file. If you passed nestedhvm=1,
you can start both nested PV and HVM guests.

Re: what's the type of nested xen? HVM or PV?

[Ian Campbell]

On Mon, 2016-01-04 at 12:52 +0000, Stefano Stabellini wrote:
> On Thu, 24 Dec 2015, quizyjones wrote:
> > Happy Holiday, guys. God tell me that I should work this out before
> > celebrate ; )I create a HVM first, then
> > compile Xen on it. The dom0 of this Xen is a PV. So is this nested xen
> > a HVM or a PV? It's hard to differentiate
> > when concerning to enable events as only HVM supports events.
> 
> Xen itself, the hypervisor, is neither HVM or PV. HVM and PV are types
> of virtual machines; the distinction doesn't apply to the hypervisor.

I think it's a little more subtle (AKA complicated) than that.

The L1 Xen is running "bare metal" inside what L0 Xen sees as an HVM guest.

However the L1 Dom0 is running PV, but it is PV WRT the L1 Xen, not the L0
Xen. From the L0's point of view the combination of L0 Xen+Dom0 remains
HVM.

In fact the PV L1 Dom0 might even be able to see some "PVHVM" like aspects
of the L0 HVM domain in which it is running, although typical
configurations don't (or can't) make use of that.

I'm not sure what the original "enable events" is referring to, so I'm not
sure whether this has clarified anything or not.

Ian.