Re: [patch 4/6] mm: merge populate and nopage into fault (fixes nonlinear)

Nick Piggin
2007-03-07T12:37:13Z

On Wed, Mar 07, 2007 at 04:22:24AM -0800, Bill Irwin wrote:
> On Wed, Mar 07, 2007 at 11:47:42AM +0100, Peter Zijlstra wrote:
> >> Well, now they don't, but it could be done or even exploited as a DoS.
>
> On Wed, Mar 07, 2007 at 12:00:36PM +0100, Nick Piggin wrote:
> > But so could nonlinear page reclaim. I think we need to restrict nonlinear
> > mappings to root if we're worried about that.
>
> Please not root. The users really don't want to be privileged. UML
> itself is at least partly for use as privilege isolation of the guest
> workload. Oracle has some of the same concerns itself, which is part of
> why it uses separate processes heavily, even: to isolate instances from
> each other.

Well non-root users could be allowed to work on mlocked regions on
tmpfs/shm. That way they avoid the pathological nonlinear problems,
and can work within the mlock ulimit.

That is, if we are worried about such a DoS.