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

Benjamin Herrenschmidt [off-list ref] wrote on 07/10/2009 23:18:21:

On Wed, 2009-10-07 at 22:46 +0200, Joakim Tjernlund wrote:

quoted

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.