port-hpcmips/54378: panic with TLB miss when attempting to reboot

[venture37%geeklan.co.uk@localhost]

>Number:         54378
>Category:       port-hpcmips
>Synopsis:       panic with TLB miss when attempting to reboot
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-hpcmips-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jul 16 09:45:00 +0000 2019
>Originator:     Sevan Janiyan
>Release:        HEAD
>Organization:
>Environment:
8.99.50
>Description:
Kernel is unable to mount mfsroot or a root fs on disk (because install is not complete), issuing reboot as the answer to root device question results in panic.

kloader: kernel file name: /mnt/netbsd
pid 0(system): trap: cpu0, TLB miss (load or instr. fetch) in kernel mode
status=0xff03, cause=0x8, epc=0x80316794, vaddr=0
tf=0x80dd1b98 ksp=0x80dd1c38 ra=0x8029a9e8 ppl=0x80dd1d20
kernel: TLB miss (load or instr. fetch) trap
Stopped in pid 0.1 (system) at netbsd:_atomic_inc_32+0x14:  lw s0,0(s1)

db> bt
0x80dd1c38: _atomic_inc_32+14 (14,0,10,0) ra 8029a0e8 sz 32
0x80dd1c58: namei_tryemulroot+1f8 (14,0,0,0) ra 8029b3d4 sz 184
0x80dd1d10: namei+4c (80dd1d58,0,0,0) ra 800060ac sz 56
0x80dd1d48: __kloader_reboot_setup+ec (80dd1d58,0,0,0) ra 8000506c sz 96
0x80dd1da8: cpu_reboot+fc (0,0,0,0) ra 8023f07c sz 24
0x80dd1dc0: parsedisk+a4 (0,0,0,0) ra 8023f950 sz 56
0x80dd1df8: setroot+2e8 (0,0,0,0)  ra 8031b320 sz 240
0x80dd1ee8: main+59c (0,0,0,0) ra 800010d8 sz 96
0x80dd1f48: kernel_text+d8 (0,0,0,0) ra 0 sz 0
User-level: pid 0.1
>How-To-Repeat:
boot generic kernel with a blank wd0 device or ramdisk kernel and issue reboot command when asked about root disk.
>Fix: