Fatal trap 9 in pmap_remove_pages

I updated an amd64 package machine to RELENG_5 yesterday, and it just died with:

Fatal trap 9: general protection fault while in kernel mode
instruction pointer     = 0x8:0xffffffff8033e0a0
stack pointer           = 0x10:0xffffffff966a2ab0
frame pointer           = 0x10:0xffffffff966a2af0
code segment            = base 0x0, limit 0xfffff, type 0x1b
                        = DPL 0, pres 1, long 1, def32 0, gran 1
processor eflags        = interrupt enabled, resume, IOPL = 0
current process         = 16123 (sh)
[thread 100214]
Stopped at      pmap_remove_pages+0x1a0:        decl    %esp
db> tr
pmap_remove_pages() at pmap_remove_pages+0x1a0
exit1() at exit1+0xeb3
sys_exit() at sys_exit+0xe
syscall() at syscall+0x4ab
Xfast_syscall() at Xfast_syscall+0xa8
--- syscall (1, FreeBSD ELF64, sys_exit), rip = 0x200915c68, rsp = 0x7fffffffd3b8, rbp = 0x1 ---

Kris