Re: [Xen-devel] Windows...

["Mark A. Williamson" <mark.williamson@xxxxxxxxxxxx>]

> How much changes are involved in the O.S.?

For a native Xen port:

* The OS memory management code must be modified to handle running in 
non-contigous physical memory (rather hard)
* The OS context switching code needs to be changed to call into Xen
* the platform initialisation code needs mostly removing and replacing with a 
small amount of Xen-specific stuff
* add various support infrastructure control interface, event channels, 
virtual interrupts
* Virtual device drivers need to be written (OK if someone takes the time to 
understand the Windows driver API)

Am I missing anything guys?

Anyhow, this requires source code access, which is the problem :-(  I heard 
talk of possibly getting Windows running under some extra virtualisation 
features without XP src code access but I think that's more of a theory at 
the moment, with no plans to work on it.

> Was Microsoft even approached with this project to see what their take on
> it is?

MS Research in Cambridge provided support for a port of Win XP to Xen 1.2 to 
be carried out locally some time ago.  I think they were really interested in 
it as a research platform rather than a product, which is fair enough - 
Microsoft have their own virtualisation platform, so I imagine they'd 
concentrate on that.

> Next generation CPU / Intel's VT, how soon can we expect a Xen 
> release to support this?

In-Xen support for VT is present, although I'm not sure the corresponding 
userspace support code is checked in yet.  I don't think Intel are disclosing 
when VT hardware will be released, however.

> Given all of the above, what are the other challenges involved in
> supporting Windows on Xen and what sort of timeline are we looking at?

Since there's VT code being integrated into Xen currently it seems reasonable 
to assume that when VT hardware comes out, Windows will Just Work (TM) but I 
don't know the concrete plans.  I may be wrong...

HTH,
Mark


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