Re: [PATCH] stubdom: foreignmemory: Fix build after 0dbb4be739c5

[Juergen Gross <jgross@xxxxxxxx>]

On 13.07.21 16:28, Jan Beulich wrote:
> On 13.07.2021 16:23, Juergen Gross wrote:
> > On 13.07.21 16:19, Julien Grall wrote:
> > > On 13/07/2021 15:14, Jan Beulich wrote:
> > > > > And I don't think it should be named XC_PAGE_*, but rather XEN_PAGE_*.
> > > > Even that doesn't seem right to me, at least in principle. There
> > > > shouldn't
> > > > be a build time setting when it may vary at runtime. IOW on Arm I think a
> > > > runtime query to the hypervisor would be needed instead.
> > > Yes, we want to be able to use the same userspace/OS without rebuilding
> > > to a specific hypervisor page size.
> > This define is used for accessing data of other domains. See the define
> > for XEN_PAGE_SIZE in xen/include/public/io/ring.h
> >
> > So it should be a constant (minimal) page size for all hypervisors and
> > guests of an architecture.
> But that's only because of limitations baked into ring.h. For example,
> a grant shouldn't be (address,attributes), but (address,order,attributes).
> A frontend running in an OS with 16k page size could then still announce
> a single ring "page", and a backend running in an OS with 4k page size
> would still have no trouble mapping that ring. (The other way around
> would of course get more interesting.)
Right. The current interfaces don't provide this ability. For those the
minimal size is "the right thing" IMO.


Juergen

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