kern/56721: nvmm fails on older linux kernels

[schaecsn%gmx.net@localhost]

>Number:         56721
>Category:       kern
>Synopsis:       nvmm fails on older linux kernels
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Thu Feb 17 17:25:00 +0000 2022
>Originator:     Stefan Schaeckeler
>Release:        2021Q4
>Organization:
>Environment:
NetBSD xxx 9.2 NetBSD 9.2 (GENERIC) #0: Wed May 12 13:15:55 UTC 2021  mkrepro%mkrepro.NetBSD.org@localhost:/usr/src/sys/arch/amd64/compile/GENERIC amd64

>Description:
nvmm crashes on Linux kernels 1.2.13 and 2.0.36, but not on 2.2.18.

>How-To-Repeat:
Download a Linux distribution with said kernel version, say suse 6.0 (kernel 2.0.36) and boot it with nvmm enabled:

$ wget https://archive.org/download/suse-6.0_release_i386/SU6001.001.ISO

$ qemu-system-i386 -accel nvmm -cdrom  SU6001.001.ISO  -m 64M
NetBSD Virtual Machine Monitor accelerator is operational
qemu-system-i386: NVMM: Unexpected VM exit code 0xffffffffffffffff [hw=0x9]
qemu-system-i386: NVMM: Failed to execute a VCPU.
Abort trap (core dumped)

Qemu crashes while the Linux kernel boots up.

Booting the same iso without nvmm enabled does not crash qemu

$ qemu-system-i386 -cdrom  SU6001.001.ISO  -m 64M 


>Fix: