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Re: [Xen-devel] [SPAM] how does hypervisor isolates DomU from Dom0

To: Tapas Mishra <mightydreams@xxxxxxxxx>
Subject: Re: [Xen-devel] [SPAM] how does hypervisor isolates DomU from Dom0
From: Pasi Kärkkäinen <pasik@xxxxxx>
Date: Sun, 15 Aug 2010 23:48:14 +0300
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On Mon, Aug 16, 2010 at 01:55:25AM +0530, Tapas Mishra wrote:
> I am not clear with the working of hypervisor xen.
> How does an instruction executed by kernel in Ring0 of DomU gets
> mapped or executed by hypervisor and then is excuted in Dom0.
> Is this thing some where on the wiki page?

Xen hypervisor runs in ring0.
Xen PV domUs don't run in ring0, instead they run in ring1.

In case of Xen HVM guests the Xen hypervisor runs in ring -1,
with help of the CPU virtualization extensions (Intel VT / AMD-V), 
so the HVM guest kernel can run in it's own private virtual ring0.

And what do you mean with "then is executed in dom0" ?

Dom0 is another guest VM, but it has some more privileges 
(direct access to the hardware) and responsibilities 
(run management toolstack and provide virtual disks and nics for other guests).

-- Pasi

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