port-xen/51526: NetBSD-7 panic on lenovo x42 and x200 with hypervisor_mmu_update failed

[mk%steepath.eu@localhost]

>Number:         51526
>Category:       port-xen
>Synopsis:       NetBSD-7 panic on lenovo x42 and x200 with hypervisor_mmu_update failed
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Oct 03 16:45:00 +0000 2016
>Originator:     Mathieu Kerjouan
>Release:        NetBSD-7.0
>Organization:
steepath
>Environment:
NetBSD 7.0 NetBSD 7.0 (XEN3_DOM0.201509250726Z) amd64
>Description:
NetBSD XEN3_DOM0 kernel crash during boot on Xen (xen41, xen42, xen45 and xen46) with some hardware. This was discovered during installing test server on some old computer. 

Lenovo x42 (dual-core, 4GB RAM):

 - crash: netbsd7 + xenkernel42 
 - crash: netbsd7 + xenkernel45 
 - crash: netbsd7 + xenkernel46 

Lenovo x200t (dual-core i7, 8GB RAM)

 - ok: netbsd6.1.5 + xen42
 - ok: netbsd6.1.5 + xen45
 - crash: netbsd7 + xen41
 - crash: netbsd7 + xen42
 - crash: netbsd7 + xen46

QEMU 2.7.0 (1CPU, 1024MB RAM, on voidlinux)

 - ok: netbsd7 + xen41
 - ok: netbsd7 + xen42
 - ok: netbsd7 + xen46
 - ok: netbsd6.1.5 + xen41
 - ok: netbsd6.1.5 + xen42

My configuration is simple:

  root (/) = 10GB
  swap = 128MB
  no extra package (only xenkernel)
  installed from binaries

I don't have any output to give you (laptops doesn't have serial ports). I will try to use usb serial port to give you more information concerning this bug. Here the last message from dmesg with db:

  cpu0(0):
    0x0000000008e09ce0: 0x0000000001000017
    kpm_pdir[0]! 0x1376f7027
  panic: HYPERVISOR_mmu_update failed, ret -16

  fatal breakpoint trap in supervisor mode
  trap type 1 code 0 rip fffffff80207475 cs e030 rflags 246 cr2 0
    ilevel 8 rsp ffffffff816f1700
  curlwp 0xffffffff80c606a0 pid 0.1 lowest kstack 0xffffffff816ef2c0

>How-To-Repeat:
All error are reproducible with manual build or with binary from officials NetBSD repositories. Just do a standard Xen minimal installation based on tutorial from NetBSD website or in the web. My installation steps:

 1. installing NetBSD-7.0 amd64 from scratch
 2. installing NetBSD-7.0 XEN3_DOM0 kernel
 3. configuring /boot.cfg
 4. reboot
 5. switch to Xen kernel during boot
 6. crash on Lenovo x42 and Lenovo x200t

After doing my first install on lenovo x200t, I installed NetBSD on qemu (work well), and copied this setup on usb flash drive. 
>Fix:
Switch to NetBSD-6.1.5 (work well on it).