kern/53487: xen dom0 crash when reboot of domU

[kiers%xs4all.nl@localhost]

>Number:         53487
>Category:       kern
>Synopsis:       xen dom0 crash when reboot of domU
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Tue Jul 31 14:25:00 +0000 2018
>Originator:     Bert Kiers
>Release:        NetBSD 8.0, Xen 4.11.0nb0
>Organization:
>Environment:
NetBSD esmeralda.quipama.co 8.0 NetBSD 8.0 (XEN3_DOM0) #0: Thu Jul 26 01:09:53 CEST 2018  kiers%yvresse.boppelans.net@localhost:/tmp/obj330/sys/arch/amd64/compile/XEN3_DOM0 amd64
>Description:
When I reboot a Linux domU, dom0 crashes:

fatal page fault in supervisor mode
trap type 6 code 0 rip 0xffffffff80239626 cs 0xe030 rflags 0x10206 cr2 0xffffa0012f71f000 ilevel 0x6 rsp 0xffffa0012f0bf
b88
curlwp 0xffffa0000e7326a0 pid 388.1 lowest kstack 0xffffa0012f0bc2c0
panic: trap
cpu0: Begin traceback...
vpanic() at netbsd:vpanic+0x140
snprintf() at netbsd:snprintf
trap() at netbsd:trap+0x953
--- trap (number 6) ---
xennetback_evthandler() at netbsd:xennetback_evthandler+0x4e
Xresume_xenev6() at netbsd:Xresume_xenev6+0x47
--- interrupt ---
Xspllower() at netbsd:Xspllower+0xe
sys_ioctl() at netbsd:sys_ioctl+0x101
syscall() at netbsd:syscall+0x9c
--- syscall (number 54) ---
753aff0fedfa:
cpu0: End traceback...

dumping to dev 0,1 (offset=67110591, size=0): not possible
rebooting...
(XEN) Hardware Dom0 shutdown: rebooting machine
(XEN) Resetting with ACPI MEMORY or I/O RESET_REG.

This is 100% repeatable.  

This is not new in NetBSD8.0 or in Xen 4.11.  ISTR that I did not see the 'fatal page fault' in older Xen or NetBSD - just poof reboot.

No difference if I type 'reboot' in the domU or 'xl shutdown' in dom0

This happens with Debian 9.5 and Ubuntu 17.10 as domU, not with NetBSD as domU, nor with FreeBSD as domU.

See http://netbsd.itsx.net/xenshutdown/ for 'dmesg', 'xl dmesg', /boot.cfg, domU config.

Otherise the system is stable with FreeBSD, NetBSD, Linux domUs for weeks.
>How-To-Repeat:
reboot Linux domU
>Fix: