linux-kernel - Re: [PATCH] fix/improve generic page table walker

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Message-ID: <20090312122441.46782f9b@skybase>
Date:	Thu, 12 Mar 2009 12:24:41 +0100
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Martin Schwidefsky <schwidefsky@...ibm.com>
Cc:	Matt Mackall <mpm@...enic.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Gerald Schaefer <gerald.schaefer@...ibm.com>,
	akpm@...ux-foundation.org
Subject: Re: [PATCH] fix/improve generic page table walker

On Thu, 12 Mar 2009 11:19:16 +0100
Martin Schwidefsky <schwidefsky@...ibm.com> wrote:

> On Thu, 12 Mar 2009 09:33:35 +0100
> Martin Schwidefsky <schwidefsky@...ibm.com> wrote:
> 
> > > I've gone to lengths to keep VMAs out of the equation, so I can't say
> > > I'm excited about this solution.  
> > 
> > The minimum fix is to add the mmap_sem. If a vma is unmapped while you
> > walk the page tables, they can get freed. You do have a dependency on
> > the vma list. All the other page table walkers in mm/ start with the
> > vma, then do the four loops. It would be consistent if the generic page
> > table walker would do the same.
> > 
> > Having thought about the problem again, I think I found a way how to
> > deal with the problem in the s390 page table primitives. The fix is not
> > exactly nice but it will work. With it s390 will be able to walk
> > addresses outside of the vma address range.
> 
> Ok, the patch below fixes the problem without vma operations in the
> generic page table walker. We still need the mmap_sem part though.

Hmm, thinko on my part. If would need the address of the pgd entry to do
what I'm trying to achieve but I only have the pgd entry itself. Back
to the vma operation in walk_page_range I'm afraid.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.

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