[PATCH 4/6] 8xx: Tag DAR with 0x00f0 to catch buggy instructions.

[Joakim Tjernlund]

Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 08/10/2009 00:21:24:
>
> On Thu, 2009-10-08 at 00:13 +0200, Joakim Tjernlund wrote:
> > Benjamin Herrenschmidt <benh at kernel.crashing.org> wrote on 07/10/2009 23:18:21:
> > >
> > > On Wed, 2009-10-07 at 22:46 +0200, Joakim Tjernlund wrote:
> > > > dcbz, dcbf, dcbi, dcbst and icbi do not set DAR when they
> > > > cause a DTLB Error. Dectect this by tagging DAR with 0x00f0
> > > > at every exception exit that modifies DAR.
> > > > Test for DAR=0x00f0 in DataTLBError and bail
> > > > to handle_page_fault().
> > >
> > > Why not -1 ? :-)
> >
> > Because 0x00f0 is already in use in the TLB fast path, saves one insn.
>
> But will cause weird things if the user really uses 0xf0 (though granted
> that's unlikely :-)

Yeah, you will most likely end up with a segv anyway.