linux-kernel - Re: [rfc][patches] fix for munmap/truncate races

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Message-ID: <20120318220751.GD6589@ZenIV.linux.org.uk>
Date:	Sun, 18 Mar 2012 22:07:51 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [rfc][patches] fix for munmap/truncate races

On Sun, Mar 18, 2012 at 10:06:10PM +0000, Al Viro wrote:
> On Sun, Mar 18, 2012 at 03:01:08PM -0700, Linus Torvalds wrote:
> > On Sun, Mar 18, 2012 at 12:07 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> > > - ? ? ? tlb_finish_mmu(&tlb, 0, end);
> > > + ? ? ? tlb_finish_mmu(&tlb, 0, -1);
> > 
> > Hmm. The fact that you drop the end pointer means that some
> > architectures that optimize the TLB flushing for ranges now
> > effectively can't do it any more.
> > 
> > Now, I think it's only ia64 that really is affected, but it *might* matter.
> > 
> > In particular, ia64 has some logic for "if you only flush one single
> > region, you can optimize it", and the region sizes are in the
> > terabytes. And I'm pretty sure you broke that - I'm just not entirely
> > sure how much we care.
> 
> Nope - ia64 check explicitly for precisely that case:
[snip]
... and everything else doesn't look at start or end at all.
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