Re: Another question about self-paging

[Bas Wijnen]

On Mon, Oct 31, 2005 at 06:10:51PM +0200, Paavo Parkkinen wrote:
> On Mon, 31.10.2005 at 09:31 -0500, Jonathan S. Shapiro wrote:
> > On Mon, 2005-10-31 at 13:29 +0200, Paavo Parkkinen wrote:
> > > On Sun, 30.10.2005 at 16:55 -0500, Jonathan S. Shapiro wrote:
> > > > There is a meta-level problem with self-paging. It is predicated on the
> > > > assumption that one application should be informed about pressures
> > > > resulting from the behavior of other applications.
> > > 
> > > Why is this a problem?
> > 
> > Because any story about security begins with the goal that for any two
> > process A and B, it should be possible to prevent communication from A
> > to B. If B is asked to reduce its working set in response to an action
> > by A, then communication has occurred.
> 
> I understand this completely. I just don't see how a demand to page
> out a page is communication from a process A to a process B. To me it
> seems like communicating about the state of the system to a process A.
> Is this also forbidden? Why?

Process B can influence the state of the system and thus ensure that A gets
notified.  If A and B cooperate, they can use this as a communication channel.
Appearantly it is even a high-bandwidth channel (I didn't expect this).

Thanks,
Bas

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