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Date: Tue, 18 Aug 2009 10:14:09 +1000
From: Paul Mackerras <paulus@samba.org>
To: Kumar Gala <galak@kernel.crashing.org>
Subject: Re: [PATCH 1/3 v3] powerpc/32: Always order writes to halves of
	64-bit PTEs
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Kumar Gala writes:

> On Aug 17, 2009, at 6:00 PM, Paul Mackerras wrote:
> 
> > On 32-bit systems with 64-bit PTEs, the PTEs have to be written in two
> > 32-bit halves.  On SMP we write the higher-order half and then the
> > lower-order half, with a write barrier between the two halves, but on
> > UP there was no particular ordering of the writes to the two halves.
> >
> > This extends the ordering that we already do on SMP to the UP case as
> > well.  The reason is that with the perf_counter subsystem potentially
> > accessing user memory at interrupt time to get stack traces, we have
> > to be careful not to create an incorrect but apparently valid PTE even
> > on UP.
> >
> > Signed-off-by: Paul Mackerras <paulus@samba.org>
> > ---
> > arch/powerpc/include/asm/pgtable.h |    6 +++---
> > 1 files changed, 3 insertions(+), 3 deletions(-)
> 
> Just out of interest did you end up hitting this in testing?

No.  Ben told me he wanted this change, so I did what I was told. :)

Paul.