Re: [PATCH] x86/mm: remove the linear mapping of the p2m tables

[Tim Deegan <tim@xen.org>]

At 15:58 +0100 on 13 Sep (1347551914), Keir Fraser wrote:
> On 13/09/2012 15:42, "Tim Deegan" <tim@xen.org> wrote:
> 
> >> Is that also going to remain true when we won't be able to 1:1-
> >> map all of the memory anymore once we break the current 5Tb
> >> barrier? If not, it would probably be worthwhile keeping that
> >> code.
> > 
> > Ah, 5TB is a smaller limit than I thought we had.  Yes, better leave it
> > alone, so.  Though TBH finding some way to use a bit more virtual
> > address space for Xen seems like a good idea anyway, since this won't be
> > the only place we'll want to avoid TLB flushes.
> 
> For HVM or PVH guests, where this HAP code would be used, clearly Xen can
> use all the virtual address space it wants. It will almost certainly make
> sense for Xen to have a 1:1 physical mapping of all memory when running such
> a guest, and only do mapcache type tricks when running legacy PV guests.

This is also used for shadowed guests, including autotranslated PV
guests, if anyone cares about them any more.  I got the impression that
they're superseded by the pvh stuff; is that right?

If that's the case, then let's commit to having a bigger 1-1 map on HVM
guetst when the time comes to extend past 5TB, and remove this linear
map after all. 

Tim.