kern/55406: NVMM panic on qemu start on intel

[nia%pkgsrc.org@localhost]

>Number:         55406
>Category:       kern
>Synopsis:       NVMM panic on qemu start on intel
>Confidential:   no
>Severity:       critical
>Priority:       high
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jun 22 12:40:00 +0000 2020
>Originator:     nia
>Release:        -current (and 9.0)
>Organization:
>Environment:
NetBSD r 9.99.64 NetBSD 9.99.64 (R) #12: Sun May 31 09:31:31 IST 2020  nia@r:/home/nia/src/sys/arch/amd64/compile/obj/R amd64
>Description:
After starting a QEMU VM with -accel nvmm, I get this (apparently) nondeterministic panic. This is an intel CPU.

fatal privileged instruction fault in supervisor mode                                                                                                                         
trap type 0 code 0 rip 0xffffffff813ed454 cs 0x8 rflags 0x10246 cr2 0x77e2d8c1d000 ilevel 0 rsp 0xffffcb80c21e2d90                                                            
curlwp 0xffffec096c4584c0 pid 24690.13443 lowest kstack 0xffffcb80c21df2c0

db> crash> callout
    ticks  wheel               arg  func
crash: _kvm_kvatop(0)
crash: kvm_read(0x0, 16592): invalid translation (invalid level 4 PDE)
db> crash> bt
_KERNEL_OPT_NARCNET() at 0
_KERNEL_OPT_NARCNET() at 0
sys_reboot() at sys_reboot
db_reboot_cmd() at db_reboot_cmd
db_command() at db_command+0x127
db_command_loop() at db_command_loop+0xa6
db_trap() at db_trap+0xe6
kdb_trap() at kdb_trap+0xe1
trap() at trap+0x2b7
--- trap (number 0) ---
vmx_vmcs_enter() at vmx_vmcs_enter+0xe3
vmx_vcpu_create() at vmx_vcpu_create+0x144
nvmm_ioctl() at nvmm_ioctl+0x292
sys_ioctl() at sys_ioctl+0x550
syscall() at syscall+0x26e
--- syscall (number 54) ---
77e2d27681ba:
>How-To-Repeat:

>Fix: