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Re: [Xen-users] Prohibit to run Xen inside guest VM?

On Tue, Dec 15, 2009 at 12:59 PM, Jun Koi <junkoi2004@xxxxxxxxx> wrote:
>>>> Technically the only way you could run nested Xen is by using a HVM
>>>> domU. Even then you'd get close to dead snail performance, and you can
>>>> only have PV guests.
>>> Why we can only have PV guests, but not HVM?
>>> I know that currently nested hypervisor is not good in performance,
>>> but that might very well change in the future.
>> HVM requires a special CPU feature (AMD-V or intel-VT) that can only
>> be used by the hypervisor, and not by domU. Which is why you can't
>> have nested HVM guest or (in the case of Windows) nested Hyper-V
>> guests.
> Yes, but most machines now already have virtualization capable CPU. I
> dont think the ISP uses very old machine that is without VT-x or
> AMD-V.

The OS that's running inside HVM domU will NOT be able to utilize
intel-vt or amd-v.
That's why nested HVM domU is not possible.

> I have some more questions:

As Rob said, you'd probably get better answer for those questions on
another list.


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