[RFC] hvm-stub for ia64

[tgingold@free.fr]

Hi,

this is my initial work on hvm-stub domains.
HVM-stub domains are a mix of PV and HVM: it requires VT extension but
look externally as a PV domain.

All the io emulation is done within the domain by a stub firmware.  This
layer translates raw IO accesses to PV commands, ie it can run unmodified
linux without running qemu-dm.

Currently it works only for ia64 and can boot linux (serial console).
I cross-post to xen-devel because I can be of a general interest.

I'd plan to submit patches soon but here is a preview.

Part 1: tools/ - modification to start an hvmstub domain (small)
Part 2: xen/ - IO reflection (small)
Part 3: extra/stubfw - stub firmware (large)

Change to common files are rather small and this is a good news.
The stub firmware is more a proof of concept and need serious enhancement.
It is just minimal to be able to boot linux (ie serial console and one ide
disk).

I am not sure where should go stubfw, so if anyone has suggestions...

Comments are welcome,
Tristan.