port-xen/46057: NetBSD/Xen DOM-U crash

[dieter.NetBSD%pandora.be@localhost]

>Number:         46057
>Category:       port-xen
>Synopsis:       NetBSD/Xen DOM-U crash
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    port-xen-maintainer
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Feb 20 07:55:00 +0000 2012
>Originator:     dieter roelants
>Release:        6.0_BETA
>Organization:
>Environment:
NetBSD netbsd-u2.inflamm 6.0_BETA NetBSD 6.0_BETA (SIMULT.domu) #15: Sat Feb 18 
19:16:16 CET 2012  
dieter@netbsd-u2.inflamm:/build/obj/sys/arch/amd64/compile/SIMULT.domu amd64
>Description:

I had a Xen guest crash like this:

uvm_fault(0xffffa000034dea50, 0x0, 1) -> e
fatal page fault in supervisor mode
trap type 6 code 0 rip ffffffff801d0c8e cs e030 rflags 10246 cr2  0 cpl 0 rsp 
ffffa00044d078f0
kernel: page fault trap, code=0
Stopped in pid 383.1 (tmux) at  netbsd:sysctl_doeproc+0xd63:    movq    0(%rax),
%rdx
sysctl_doeproc() at netbsd:sysctl_doeproc+0xd63
sysctl_dispatch() at netbsd:sysctl_dispatch+0xb2
sys___sysctl() at netbsd:sys___sysctl+0xeb
syscall() at netbsd:syscall+0xc4
ds          1298
es          c2f0
fs          1000
gs          d7c0
rdi         0
rsi         ffffffff8033950d    copyright+0x422d
rbp         ffffa00044d07ad0
rbx         ffffa0000375d7c0
rdx         0
rcx         ffffa000095a1298
rax         0
r8          2
r9          ffffa000095a10ac
r10         1f00000014
r11         0
r12         ffffa000095a1000
r13         2a8
r14         ffffa00009725900
r15         ffffa000037645a0
rip         ffffffff801d0c8e    sysctl_doeproc+0xd63
cs          e030
rflags      10246
rsp         ffffa00044d078f0
ss          e02b
netbsd:sysctl_doeproc+0xd63:    movq    0(%rax),%rdx

The kernel config is XEN3_DOMU, with some compat options, file systems, pseudo 
devices disabled, and (unfortunately) also without DIAGNOSTIC, DEBUG. 
MULTIPROCESSOR is enabled, but the machine has but one vcpu.
>How-To-Repeat:
It only happened once, so far. The machine was building pkgsrc stuff in a tmux. 
There's a good chance the crash happened when I detached the tmux.
>Fix: