port-xen/55291: panic: HYPERVISOR_mmu_update failed, ret: -16

[prlw1%cam.ac.uk@localhost]

>Number:         55291
>Category:       port-xen
>Synopsis:       panic: HYPERVISOR_mmu_update failed, ret: -16
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sat May 23 15:25:00 +0000 2020
>Originator:     Patrick Welche
>Release:        NetBSD-9.99.63/amd64 of 22 May 2020 + jdolecek's patch for PR 55285
>Organization:
>Environment:
Xen 4.11.3nb2
>Description:
With jdolecek's patch for PR 55285, the XEN3_DOM0 kernel boots to multiuser, and then panics:

Starting cupsd.
Starting cron.
The following components reported failures:
    /etc/rc.d/sysctl
See /var/run/rc.log for more information.
Sat May 23 16:11:29 BST 2020
[ 239.1600116] xpq_flush_queue: 1 entries (0 successful) on cpu0 (0)
[ 239.1600116] panic: HYPERVISOR_mmu_update failed, ret: -16

[ 239.1600116] cpu0: Begin traceback...
[ 239.1600116] vpanic() at netbsd:vpanic+0x146
[ 239.1600116] snprintf() at netbsd:snprintf
[ 239.1600116] xpq_queue_machphys_update() at netbsd:xpq_queue_machphys_update
[ 239.1600116] pmap_enter_ma() at netbsd:pmap_enter_ma+0x69d
[ 239.1600116] pmap_enter() at netbsd:pmap_enter+0x58
[ 239.1600116] udv_fault() at netbsd:udv_fault+0x100
[ 239.1600116] uvm_fault_internal() at netbsd:uvm_fault_internal+0x518
[ 239.1600116] trap() at netbsd:trap+0x66c
[ 239.1600116] --- trap (number 6) ---
[ 239.1600116] 7237b698b62f:
[ 239.1600116] cpu0: End traceback...

[ 239.1600116] dumping to dev 168,1 (offset=33554431, size=0): not possible
[ 239.1600116] rebooting...
(XEN) Hardware Dom0 shutdown: rebooting machine
(XEN) Resetting with ACPI MEMORY or I/O RESET_REG.

>How-To-Repeat:
Boot XEN3_DOM0
>Fix: