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

[Juergen Gross <jgross@suse.com>]

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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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