AFAIK dom0 is pv-domain.
All interrupts are handled by xen and passed down to dom0 via events 
(kinda internal  xen interrupt-like stuff). PV kernel accepts them and 
process as normal interrupts.

Is Xen use IOMMU to protect itself from misbehave devices or not... I'm 
not sure.

On 11.10.2012 10:16, maheen butt wrote:
> Hi all,
>
> I'm investigating the source code of Xenified kernel. From 
> documentations related to
> Xen told me that all guest domains run in less privilege mode ( ring 1 
> in case of x86).
> Dom0 is also running in ring 1. But it can have direct access to IO 
> devices. It means
> Dom0 has a special bahaviour that it is running in ring1 but can 
> directly access IO devices.
> How Dom0 access IO devices directly?
> how can I relate this special way of Dom0 with its source code?
>
>
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