amd64 pmap panic

[Patrick Welche <prlw1%cam.ac.uk@localhost>]

A amd64 kernel built from today's source just panicked with:

panic: kernel diagnostic assertion "(opte & (PG_V | PG_W)) != PG_W" failed: 
file "../../../../arch/x86/x86/pmap.c", line 636
fatal breakpoint trap in supervisor mode
trap type 1 code 0 rip ffffffff804c0e95 cs 8 rflags 246 cr2 7f7ffdc00158 cpl 0 
rsp ffff800054fb2790
Stopped in pid 21947.1 (sh) at  netbsd:breakpoint+0x5:  leave
db{0}>

pmap_enter()
uvm_fault_internal()
trap()
uvm_fault()

(cpu 1 doesn't give a trace)

Thoughts?

Cheers,

Patrick