(In reply to comment #7)
> (In reply to comment #6)
> > (In reply to comment #5)
> > > (In reply to comment #3)
> > > > Does it still happen if you drop the PTE patches?
> > > 
> > > Is that stop poisoning the GART TLB?
> > 
> > Ok ignore that :-) I didn't spot the rs600
> 
> It applies to all asics from rs600 forward.

Ahh, in the meantime I've now built with 

optimize SI VM handling + use lower_32_bits where appropriate reverted - the
latter just so I could revert the former.

I'll see if I am stable over the next couple of days like this.