[PATCH] 8xx: fix user space TLB walk in dcbX fixup

[Joakim Tjernlund]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 12/01/2010 09:44:09:
>
> On Tue, 2010-01-12 at 08:07 +0100, Joakim Tjernlund wrote:
> > Benjamin Herrenschmidt <benh at 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 at 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 :-)

Yeah, but this is nothing new to 8xx users.
The TLB handlers (and possible other parts too) has always had this limitation.
I don't think anyone cares since this is a small embedded CPU.

       Jocke