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

thanks to everyone who replied! What I was thinking of was something along the lines of Daniel's suggestion below, i.e. if the VMX architecture makes it possible to setup enough proper traps etc. so that you can actually "cheaply" emulate all these VMX registers/features and thus have multiple, nested HVM's. I don't know if it's useful but it is at least interesting to think about how it would work and how big/small a performance cost you could get away with if you had, say, 10 nested HVM's with Linux or something running in the innermost ;) I guess the emulation cost will be bigger for the "non-primary" HVM's (the primary being the one running closest to the hardware). 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.

> From: stodden@xxxxxxxxxx
> To: bguthro@xxxxxxxxxxxxxxx
> Date: Thu, 31 Jan 2008 14:33:46 +0100
> Subject: Re: [Xen-devel] Xen inside Xen with VMX?
> CC: xen-devel@xxxxxxxxxxxxxxxxxxx; paradigm__82@xxxxxxxxxxx
> On Thu, 2008-01-31 at 07:07 -0500, Ben Guthro wrote:
> > Current VT implementations do not have this ability, AFAIK.
> Indeed. There's only one root mode, and the processor has no concept of
> recursively stacking roots and accompanying protection levels on top of
> each other.
> Nonetheless, root mode could be emulated, i.e. via shadow VMCBs,
> optional shadow NPTs and emulation of the respective instruction subset.
> Would suffer from the same (most probably solvable) problems regarding
> privilege compression and the like, but probably an interesting
> excercise.
> Maybe one should put it on some (nonexisting) list for interesting
> [academic] projects.
> regards,
> daniel
> --
> 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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