Re: Xen and Linux

["Dimitrie O. Paun" <dpaun@rogers.com>]

On Fri, Nov 05, 2004 at 11:28:25PM +0000, Ian Pratt wrote:
> It would be very cool ;-) We might even get distros to ship it on
> their install CD...

Exactly where I was going ... :)

> There's one simple src change in arch Xen that has some quite far
> reaching consequences: we change FIXADDR_TOP which effectively
> gives us a 64MB whole at the top of the guest's VM space where
> Xen lives. This constant gets compiled into a bunch of different
> functions (though I believe it doesn't make it into modules
> --phew!).

Oh. Is there any way that the kernel can reuse that space
if it figures that it's not running under Xen. I haven't
looked too closely at the kernel's memory management, but
I seem to remember the zone allocators...

> I suspect it would be unpopular to make FIXADDR_TOP a variable,
> and it turns out to be a tricky thing to runtime patch. I think
> we just have to have arch-xen specific versions of all of the
> functions that use it.

Yes, in which case we could maybe turn it *there* into a variable.

> The simplest way to do this would be to have a tool that builds
> an x86 and xen kernel then merges the two together. Sounds a bit
> gross, but I think it would work quite well.

Maybe, but it would be bigger, and this maybe a problem for small
devices. Anyhow, not very satisfying :)

> Probably the cleanest solution of all would be to make all the
> other architectures adopt Xen's nice clean interfaces and then
> have stub routines for talking to the grotty realty of real
> hardware. Might be a hard one to sell to Linus et al though ;-)

Yeah, I'd think this would be the preferable route. How large
would such a patch be?. It may be worth it to float it on LKML 
to see the reaction :)

-- 
Dimi.


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