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

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
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.


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