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

From: Benjamin Herrenschmidt <[email-masked]>
Date: Thu, 08 Oct 2009 09:21:24 +1100

On Thu, 2009-10-08 at 00:13 +0200, Joakim Tjernlund wrote:
> Benjamin Herrenschmidt <[email-masked]> 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 :-)

Cheers,
Ben.