Re: [Xen-devel] [PATCH V4] xen/arm: domain_build: allocate lowmem for dom0 as much as possible

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

Hello Julien,

Please see my comments below:

> From my understanding of what you say, the problem is not because domU is 
> using memory above 4GB but the fact that >the backend driver does not take 
> the right decision

Yep, the problem could be treated in such a way.

> (e.g using bounce buffer when required).
I suppose unacceptable performance drop for such kind of solution.

An alternative here could be reverting of the FE-BE interaction scheme
in a following way: BE side domain provides buffers and maps them to
the FE side domain. Some time ago we estimated this approach as huge
architecture change and enormous implementation efforts. Also it does
answer to the next question:

> The guest should be IPA agnostic and not care how the physical device is 
> working when using PV drivers. So for me,
> this should be fixed in the DOM0 OS.
Do you consider driver domain guests?

Sincerely,
Andrii Anisov.

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