Re: [PATCH 3/6] ksm: change the KSM_REMOVE_MEMORY_REGION ioctl.

Chris Wright
2009-05-06T17:13:42Z

* Hugh Dickins (hugh@veritas.com) wrote:
> On Wed, 6 May 2009, Chris Wright wrote:
> > Another
> > question of what to do w/ VM_LOCKED, should that exclude VM_MERGE or
> > let user get what asked for?
>
> What's the issue with VM_LOCKED? We wouldn't want to merge a page
> while it was under get_user_pages (unless KSM's own, but ignore that),
> but what's the deal with VM_LOCKED?
>
> Is the phrase "covert channel" going to come up somehow?

There's two (still hand wavy) conerns I see there. First is the security
implication: timing writes to see cow and guess the shared data for
another apps VM_LOCKED region, second is just plain old complaints of
those rt latency sensitive apps that somehow have VM_LOCKED|VM_MERGE
and complain of COW fault time, probably just "don't do that".

thanks,
-chris