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

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 fÃr Rechnertechnik und Rechnerorganisation
Institut fÃr Informatik der TU MÃnchen             D-85748 Garching
http://www.lrr.in.tum.de/~stodden         mailto:stodden@xxxxxxxxxx
PGP Fingerprint: F5A4 1575 4C56 E26A 0B33  3D80 457E 82AE B0D8 735B

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