Question regarding the DTLB Miss exceptions

[Bruce_Leonard at selinc.com]

I'm tracking a problem that's leading me through DSI and DTLB miss 
exceptions on an MPC8347 (e300c1 core), and I've come across an oddity 
that I'm hoping someone can explain.

When a DTLB Miss exception can't find a PTE for the virtual address being 
written/read, it dummies up the SPRs for a DSI exception and then calls 
directly into the DSI exception code.  Just before the DTLB miss code 
stores a value into DSISR it sets bit 2, which for a DSI exception is a 
reserved bit and should be cleared.  There's no comment on the code 
(.../arch/powerpc/kernel/head_32.S line 619 of the 2.6.33-rc1 kernel). Can 
anyone tell me why this bit is getting set?

Thanks.

Bruce