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

[Jun Koi <junkoi2004@xxxxxxxxx>]

On Tue, Dec 15, 2009 at 2:37 PM, Fajar A. Nugraha <fajar@xxxxxxxxx> wrote:
> On Tue, Dec 15, 2009 at 10:30 AM, Jun Koi <junkoi2004@xxxxxxxxx> wrote:
>> On Tue, Dec 15, 2009 at 11:24 AM, Fajar A. Nugraha <fajar@xxxxxxxxx> wrote:
>>> On Tue, Dec 15, 2009 at 9:09 AM, Jun Koi <junkoi2004@xxxxxxxxx> wrote:
>>>> Hi,
>>>>
>>>> I am looking around to find an ISP that provides Xen VM, so I can run
>>>> whatever OS I want inside the rented guest VM.
>>>
>>> usually you don't get to run "whatever OS". Amazon EC2 is a good
>>> example. Look at what OS they support.
>>
>> The point is: once I control my VM, I can replace the OS anytime, no?
>> How can they enforce that?
>> (Suppose that they give me the HVM)
>
> That depends. Do they allow you to change domU's disks? Do they allow
> attaching ISO image? Do they give vnc console access? If all of those
> is yes, then you should be able to replace it. AFAIK they usually
> start with a prebuilt image.
>
>>
>>> 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.

I have some more questions:

1) Is it true that usually ISP only provides PV machine, but not HVM?

2) On HVM case, do they usually have rany egulation on what OS can we
install on that? Or we can do anything with the VM?

I would be very appreciated if you can kindly advise me a good ISP
providing Xen service (or please email me off list if you dont want to
public that).

Many thanks,
J

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