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

To: "Fajar A. Nugraha" <fajar@xxxxxxxxx>
Subject: Re: [Xen-users] Prohibit to run Xen inside guest VM?
From: Jun Koi <junkoi2004@xxxxxxxxx>
Date: Tue, 15 Dec 2009 16:44:45 +0900
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On Tue, Dec 15, 2009 at 4:33 PM, Fajar A. Nugraha <fajar@xxxxxxxxx> wrote:
> 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.

While it is not possible at the moment due to technical reason, I
think that will be OK in the future version of Xen.
(Some people are working on it, I believe)

>> I have some more questions:
> As Rob said, you'd probably get better answer for those questions on
> another list.

I havent seen what "Rob" said. His email didnt get to the list?


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