Re: [Xen-devel] problem with netfront.c

[Mark Williamson <mark.williamson@xxxxxxxxxxxx>]

> This looks quite interesting. Is there anything written up about the
> motivations for this design, and how it compares to other similar
> mechanisms, say, L4's grant-via-IPC system?

I don't know of much writeup beyond the details in the README and the original 
description in the 2004 OASIS paper 
(http://www.cl.cam.ac.uk/netos/papers/2004-oasis-ngio.pdf).

> Are the grant references capabilities, or how do you prevent domains
> from inventing their own?

I think they behave like capabilities.  Given a grant ref. ID, the mapping 
domain asks Xen for a mapping.  Xen uses the ID to index into the mappee's 
grant table and checks that reference gives the appropriate permissions.

> Who takes care of garbage-collecting them when 
> a domain exists or dies?

I guess a domains memory won't be deallocated until all mappings to it are 
relinquished (due to ref counting).  At this point it will be safe to throw 
away all the grant references.

> Can a domain DoS a Xen-system by allocating all 
> the grant refs in the system?

Each domain has its own grant table, so this shouldn't be a problem.

Cheers,
Mark

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