Naive question about grant/map

Marcus Völp voelp at
Fri Dec 5 11:20:45 CET 2003

Jonathan wrote:

>I am looking for a sequence in which A maps to B and B ??? to C and the
>result would look like:
>   A -> B
>   A -> C
>Is there such an operation?
One possibility would be for B to request A to map the page on behalf of 
B. This would result in the above graph. I think your question relates 
to is there a possibility for A to avoid B mapping the page directly to 
B, i.e. is there a way for A to enforce that the above graph can only be 
created as such and particularly not in the form A - B - C. Do I get 
this right?

We are currently thinking about ways to restrict communication such, 
that this particular restriction is possible. The relevant question 
thereby is:

1) Should B be allowed to send messages to C, but no mappings?
2) Should B be allowed to send messages to C, but C not back to B?

In the second case we need a way to restrict mapping such, that the 
result is to map pages read only. Otherwise a read-writable
page can be used as a back channel from C to B.


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