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RE: [Xen-devel] Xen inside Xen with VMX?

To: Morten Hansen <paradigm__82@xxxxxxxxxxx>
Subject: RE: [Xen-devel] Xen inside Xen with VMX?
From: Daniel Stodden <stodden@xxxxxxxxxx>
Date: Fri, 01 Feb 2008 11:31:51 +0100
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On Thu, 2008-01-31 at 22:14 +0100, Morten Hansen wrote:

>  But I guess that even stuff like VT-d directed I/O could be
> recursively emulated and yet still have "true" direct I/O for the
> innermost operating system.

AMD's IOMMU docs (used to?) have some useful comments regarding
emulation. Different from CPU virtualization, emulation I/O memory
management is much more interesting in practice, since different from
hvm it's not a VMM-only feature. Most operating systems would use it,
e.g. for remapping 32bit DMA-capable devices to transfers into 64bit
memory space.

Hence, emulation of the machine interface for full virtualization is
indeed quite useful, even without recursion. And yes, it would remain
effective and efficient. It's only control operations which are to be
emulated in shadow structures, running is _not_ subject to emulation.


Daniel Stodden
LRR     -      Lehrstuhl für Rechnertechnik und Rechnerorganisation
Institut für Informatik der TU München             D-85748 Garching
http://www.lrr.in.tum.de/~stodden         mailto:stodden@xxxxxxxxxx
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