Re: [PATCH v3 13/18] x86/mm: build and maintain a sparse view of the directmap

[George Dunlap <gwd@xxxxxxxxxxxxxx>]

On Wed, Oct 7, 2026 at 12:00 PM George Dunlap <gwd@xxxxxxxxxxxxxx> wrote:
> The directmap maps all of RAM, and every root page-table carries it, so
> while any guest context runs, all guest memory is reachable from Xen's
> address space.  For ASI, guest contexts are to run on a view of the
> directmap which maps only what Xen must reach through it at all times,
> leaving guest memory to transient mappings (map_domain_page()).

Note that a deeper review has found a bunch of random corner-cases,
mostly to do with allocation failures when modifying the sparse view's
pagetables.  I'm going through them; my current plan is in most cases
to add fixes after this series, to make them easier to review, unless
they're obviously core to the functionality of this patch as it is.

 -George