linux-kernel - Re: [PATCH 3/6] ksm: change the KSM_REMOVE_MEMORY

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Message-ID: <20090506170917.GE15712@x200.localdomain>
Date:	Wed, 6 May 2009 10:09:17 -0700
From:	Chris Wright <chrisw@...hat.com>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Chris Wright <chrisw@...hat.com>, Izik Eidus <ieidus@...hat.com>,
	Rik van Riel <riel@...hat.com>, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, aarcange@...hat.com,
	alan@...rguk.ukuu.org.uk, device@...ana.org, linux-mm@...ck.org,
	nickpiggin@...oo.com.au
Subject: Re: [PATCH 3/6] ksm: change the KSM_REMOVE_MEMORY_REGION ioctl.

* Hugh Dickins (hugh@...itas.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
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