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Subject: Re: [PATCH] 8xx: fix user space TLB walk in dcbX fixup
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Joakim Tjernlund <joakim.tjernlund@transmode.se>
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Date: Tue, 12 Jan 2010 19:44:09 +1100
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Cc: Scott Wood <scottwood@freescale.com>,
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On Tue, 2010-01-12 at 08:07 +0100, Joakim Tjernlund wrote:
> Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote on 12/01/2010 03:40:45:
> >
> > On Fri, 2010-01-08 at 17:46 +0100, Joakim Tjernlund wrote:
> > > The newly added fixup for buggy dcbX insn's has
> > > a bug that always trigger a kernel TLB walk so a user space
> > > dcbX insn will cause a Kernel Machine Check if it hits DTLB error.
> > >
> > > Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>
> > > ---
> > >
> > > I found this problem in 2.4 and forward ported it to 2.6. I
> > > cannot test it so I cannot be 100% sure I got it right.
> > >
> > >  arch/powerpc/kernel/head_8xx.S |    4 ++--
> > >  1 files changed, 2 insertions(+), 2 deletions(-)
> >
> > Do you have something to make sure that TASK_SIZE is never bigger than
> > 2G ? Else userspace could be all the way to 0xbfffffff ...
> 
> No, but this is 8xx :) The TLB handlers has the same "limitation" and has always
> been so.

You should send a patch to express that limitation in KConfig :-)

Cheers,
Ben.