change within last day broke nvmm

[Tobias Nygren]

Hi,

This is consistently reproducable while trying to boot Linux on nvmm.

panic: LIST_INSERT_HEAD 0xffff880000713368 x86/pmap.c:2135
vpanic()
panic()
pmap_enter_pv()
pmap_ept_enter()
uvm_fault_lower_enter()
uvm_fault_internal()
nvmm_ioctl()
sys_ioctl()
syscall()

-Tobias