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

[Tim Deegan <tim@xen.org>]

At 15:23 +0100 on 13 Sep (1347549790), Jan Beulich wrote:
> >>> On 13.09.12 at 16:01, Tim Deegan <tim@xen.org> wrote:
> > # HG changeset patch
> > # User Tim Deegan <tim@xen.org>
> > # Date 1347544824 -3600
> > # Node ID a770d1c8448d73ccf2ec36a5322532c2e3c14641
> > # Parent  5691e4cc17da7fe8664a67f1d07c3755c0ca34ed
> > x86/mm: remove the linear mapping of the p2m tables.
> > 
> > Mapping the p2m into the monitor tables was an important optimization
> > on 32-bit builds, where it avoided mapping and unmapping p2m pages
> > during a walk.  On 64-bit it makes no difference -- see
> > http://old-list-archives.xen.org/archives/html/xen-devel/2010-04/msg00981.html 
> 
> 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.

Tim.