Re: [Xen-devel] [PATCH 4 of 5] Add support for mapping grant references into HVM guests by modifying the P2M

[Steven Smith <steven.smith@xxxxxxxxxx>]

> >> I believe that Xen 32bit is still important and desired by many
> >> people. So please considere supporting that with your patch.
> > The problem is that we only have a limited number of bits available in
> > the P2M entries, which limits the number of distinct types of P2M
> > entry which we can encode.  On 32-bit Xen, that limit is eight, of
> > which seven are already used, and the grant mapping patch needs
> > another two (one for read-write maps, and one for read-only).  There
> > just isn't enough room everything we want to do.
> >
> > It'd be easy enough to make grant mapping work on 32-bit Xen if we
> > were willing to drop some other feature (populate-on-demand, say), but
> > I don't think that would be an acceptable solution.  Finding somewhere
> > else to stash the required bits would significantly complicate things,
> > and, since there aren't any particularly convincing use-cases yet for
> > even the 64-bit variant, I didn't think that would be worthwhile.
> OK, I see.
> 
> I want to try your patch. However, my Dom0 is 32bit, so Xen is 32 bit,
> too (I compiled Xen from source code). How can I compile Xen in 64bit
> for your patch now?
> 
> If it is not possible (or easy) to do that now, could you please
> provide the patch to cross compile Xen in 64bit, too?
>  That would be useful to try your patch, and also for other things.
Err...  The easy way of building a 64-bit Xen is just to install a
64-bit Linux and do a native compile from there.  It's possible, in
principle, to cross-compile it, but it's not something I've ever done,
and it requires a fair bit of fiddling to get right.  I'd recommend
that you install a 64-bit version of Linux somewhere and do the
compilation from there, rather than trying to set up cross toolchains,
unless you have absolutely no choice in the matter.

Steven.

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