linux-kernel - Re: [PATCH] Don't mlock guardpage if the stack is growing up

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Message-ID: <4DCBA2FB.3040907@redhat.com>
Date:	Thu, 12 May 2011 11:06:03 +0200
From:	Zdenek Kabelac <zkabelac@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	Milan Broz <mbroz@...hat.com>, Alasdair G Kergon <agk@...hat.com>,
	Matthew Wilcox <matthew@....cx>,
	Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz>,
	linux-kernel@...r.kernel.org, linux-parisc@...r.kernel.org,
	Hugh Dickins <hughd@...gle.com>,
	Oleg Nesterov <oleg@...hat.com>
Subject: Re: [PATCH] Don't mlock guardpage if the stack is growing up

Dne 12.5.2011 04:12, Linus Torvalds napsal(a):
> On Wed, May 11, 2011 at 1:42 AM, Milan Broz <mbroz@...hat.com> wrote:
>>
>> Another one is cryptsetup [..]
> 
> Quite frankly, all security-related uses should always be happy about
> a "MCL_SPARSE" model, since there is no point in ever bringing in
> pages that haven't been used. The whole (and only) point of
> mlock[all]() for them is the "avoid to push to disk" issue.
> 
> I do wonder if we really should ever do the page-in at all. We might
> simply be better off always just saying "we'll lock pages you've
> touched, that's it".
> 

For LVM we need to ensure the code which might ever be executed during  disk
suspend state must be paged and locked in - thus we would need MCL_SPARSE only
on several selected 'unneeded' libraries - as we are obviously not really able
to select which part of glibc might be needed during all code path (though I
guess we may find some limits).  But if we are sure that some libraries and
locale files will never be used during suspend state - we do not care about
those pages at all.

So it's not like we would always need only MCL_SPARSE all the time - we would
probably need to have some control to switch i.e.  glibc into MCL_ALL.

Zdenek
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