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Re: Xen Rust VirtIO demos work breakdown for Project Stratos

On Fri, Sep 24, 2021 at 05:02:46PM +0100, Alex Bennée wrote:
> Hi,


> 2.1 Stable ABI for foreignmemory mapping to non-dom0 ([STR-57])
> ───────────────────────────────────────────────────────────────
>   Currently the foreign memory mapping support only works for dom0 due
>   to reference counting issues. If we are to support backends running in
>   their own domains this will need to get fixed.
>   Estimate: 8w
> [STR-57] <https://linaro.atlassian.net/browse/STR-57>

I'm pretty sure it was discussed before, but I can't find relevant
(part of) thread right now: does your model assumes the backend (running
outside of dom0) will gain ability to map (or access in other way)
_arbitrary_ memory page of a frontend domain? Or worse: any domain?
That is a significant regression in terms of security model Xen
provides. It would give the backend domain _a lot more_ control over the
system that it normally has with Xen PV drivers - negating significant
part of security benefits of using driver domains.

So, does the above require frontend agreeing (explicitly or implicitly)
for accessing specific pages by the backend? There were several
approaches to that discussed, including using grant tables (as PV
drivers do), vIOMMU(?), or even drastically different model with no
shared memory at all (Argo). Can you clarify which (if any) approach
your attempt of VirtIO on Xen will use?

A more general idea: can we collect info on various VirtIO on Xen
approaches (since there is more than one) in a single place, including:
 - key characteristics, differences
 - who is involved
 - status
 - links to relevant threads, maybe

I'd propose to revive https://wiki.xenproject.org/wiki/Virtio_On_Xen

Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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