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

  • To: Juergen Gross <jgross@xxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Tue, 13 Jul 2021 16:28:15 +0200
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  • Cc: Julien Grall <jgrall@xxxxxxxxxx>, Ian Jackson <iwj@xxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Costin Lupu <costin.lupu@xxxxxxxxx>, Julien Grall <julien@xxxxxxx>
  • Delivery-date: Tue, 13 Jul 2021 14:28:27 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

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.)




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