OpenBSD in qemu freezes randomly

[Leo Unglaub]

Hi,
i have searched the list archive and found some similar reports but none 
of them found a solution for the problem. (at least not the threads i 
have found)

I run some OpenBSD 6.3 instances in a virtual environment. The host is 
some unknown Linux distribution with qemu on it. After the data center 
updated there kernels and also qemu my virtual OpenBSD instances startet 
to freeze randomly but almost always during login. They freeze up so 
hard that i cannot drop into a debugger or get any output whatsoever. 
There is not even a core dump, nothing. Just for testing purposes i 
installed a 6.2 as well and did syspatch on it just to see if the error 
happens there as well and it does. I have added a dmesg on the bottom of 
the email.

I talked to the people at the datacenter and they confirmed that they 
did a Linux kernel update at the same time as the problems started. They 
send me a link to this bug report here from Arch. They say they don't 
use Arch, but the problem described here is exactly what i experienced 
as well: https://bugs.archlinux.org/task/55231

In this ticket someone commented the following:

It looks like linux-4.12.8-1 is built with GCC: (GNU) 7.1.1 20170630, whereas 
linux-4.12.8-2 with GCC: (GNU) 7.2.0 (which apparently is still in testing)

Could there be some sort of new optimization in GCC 7.2.0 that causes my 
OpenBSD instance to crash?

I have looked around the misc@, tech@ archives and also on reddit. A lot 
of people seam to have this problem with there OpenBSD crashing after 
this quemu update. Is there something i could try in order to stabilize 
the servers?

All servers are updated via syspatch and there is only one package 
installed on them: vim. The rest is as shipped in the sets.

Thanks so much
Leo

OpenBSD 6.3 (GENERIC) #4: Sun Jun 17 11:09:51 CEST 2018
    r...@syspatch-63-amd64.openbsd.org:/usr/src/sys/arch/amd64/compile/GENERIC
real mem = 2080227328 (1983MB)
avail mem = 2010259456 (1917MB)
mpath0 at root
scsibus0 at mpath0: 256 targets
mainbus0 at root
bios0 at mainbus0: SMBIOS rev. 2.8 @ 0xf68c0 (9 entries)
bios0: vendor Hetzner version "20171111" date 11/11/2017
bios0: Hetzner vServer
acpi0 at bios0: rev 0
acpi0: sleep states S5
acpi0: tables DSDT FACP APIC HPET
acpi0: wakeup devices
acpitimer0 at acpi0: 3579545 Hz, 24 bits
acpimadt0 at acpi0 addr 0xfee00000: PC-AT compat
cpu0 at mainbus0: apid 0 (boot processor)
cpu0: Intel Xeon Processor (Skylake, IBRS), 2100.29 MHz
cpu0: 
FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,CFLUSH,MMX,FXSR,SSE,SSE2,SSE3,PCLMUL,SSSE3,FMA3,CX16,PCID,SSE4.1,SSE4.2,x2APIC,MOVBE,POPCNT,DEADLINE,AES,XSAVE,AVX,F16C,RDRAND,HV,NXE,PAGE1GB,RDTSCP,LONG,LAHF,ABM,3DNOWP,FSGSBASE,BMI1,HLE,AVX2,SMEP,BMI2,ERMS,INVPCID,RTM,MPX,AVX512F,AVX512DQ,RDSEED,ADX,SMAP,CLWB,AVX512CD,AVX512BW,AVX512VL,IBRS,IBPB,ARAT,XSAVEOPT,XSAVEC,XGETBV1,MELTDOWN
cpu0: 64KB 64b/line 2-way I-cache, 64KB 64b/line 2-way D-cache, 512KB 64b/line 
16-way L2 cache
cpu0: ITLB 255 4KB entries direct-mapped, 255 4MB entries direct-mapped
cpu0: DTLB 255 4KB entries direct-mapped, 255 4MB entries direct-mapped
cpu0: smt 0, core 0, package 0
mtrr: Pentium Pro MTRR support, 8 var ranges, 88 fixed ranges
cpu0: apic clock running at 1000MHz
ioapic0 at mainbus0: apid 0 pa 0xfec00000, version 11, 24 pins
acpihpet0 at acpi0: 100000000 Hz
acpiprt0 at acpi0: bus 0 (PCI0)
acpicpu0 at acpi0: C1(@1 halt!)
"ACPI0006" at acpi0 not configured
"PNP0A06" at acpi0 not configured
"PNP0A06" at acpi0 not configured
"PNP0A06" at acpi0 not configured
"QEMU0002" at acpi0 not configured
"ACPI0010" at acpi0 not configured
pvbus0 at mainbus0: KVM
pci0 at mainbus0 bus 0
pchb0 at pci0 dev 0 function 0 "Intel 82441FX" rev 0x02
pcib0 at pci0 dev 1 function 0 "Intel 82371SB ISA" rev 0x00
pciide0 at pci0 dev 1 function 1 "Intel 82371SB IDE" rev 0x00: DMA, channel 0 
wired to compatibility, channel 1 wired to compatibility
pciide0: channel 0 disabled (no drives)
atapiscsi0 at pciide0 channel 1 drive 0
scsibus1 at atapiscsi0: 2 targets
cd0 at scsibus1 targ 0 lun 0: <QEMU, QEMU DVD-ROM, 2.5+> ATAPI 5/cdrom removable
cd0(pciide0:1:0): using PIO mode 4, DMA mode 2
uhci0 at pci0 dev 1 function 2 "Intel 82371SB USB" rev 0x01: apic 0 int 11
piixpm0 at pci0 dev 1 function 3 "Intel 82371AB Power" rev 0x03: apic 0 int 9
iic0 at piixpm0
vga1 at pci0 dev 2 function 0 "Bochs VGA" rev 0x02
wsdisplay0 at vga1 mux 1: console (80x25, vt100 emulation)
wsdisplay0: screen 1-5 added (80x25, vt100 emulation)
virtio0 at pci0 dev 3 function 0 "Qumranet Virtio Network" rev 0x00
vio0 at virtio0: address 96:00:00:07:a0:53
virtio0: msix shared
virtio1 at pci0 dev 4 function 0 "Qumranet Virtio SCSI" rev 0x00
vioscsi0 at virtio1: qsize 128
scsibus2 at vioscsi0: 255 targets
sd0 at scsibus2 targ 0 lun 0: <QEMU, QEMU HARDDISK, 2.5+> SCSI3 0/direct fixed
sd0: 19532MB, 512 bytes/sector, 40001536 sectors, thin
virtio1: msix shared
virtio2 at pci0 dev 5 function 0 "Qumranet Virtio Memory" rev 0x00
viomb0 at virtio2
virtio2: apic 0 int 10
virtio3 at pci0 dev 6 function 0 "Qumranet Virtio Console" rev 0x00
virtio3: no matching child driver; not configured
isa0 at pcib0
isadma0 at isa0
fdc0 at isa0 port 0x3f0/6 irq 6 drq 2
com0 at isa0 port 0x3f8/8 irq 4: ns16550a, 16 byte fifo
pckbc0 at isa0 port 0x60/5 irq 1 irq 12
pckbd0 at pckbc0 (kbd slot)
wskbd0 at pckbd0: console keyboard, using wsdisplay0
pms0 at pckbc0 (aux slot)
wsmouse0 at pms0 mux 0
pcppi0 at isa0 port 0x61
spkr0 at pcppi0
usb0 at uhci0: USB revision 1.0
uhub0 at usb0 configuration 1 interface 0 "Intel UHCI root hub" rev 1.00/1.00 
addr 1
uhidev0 at uhub0 port 1 configuration 1 interface 0 "QEMU QEMU USB Tablet" rev 
2.00/0.00 addr 2
uhidev0: iclass 3/0
ums0 at uhidev0: 3 buttons, Z dir
wsmouse1 at ums0 mux 0
vscsi0 at root
scsibus3 at vscsi0: 256 targets
softraid0 at root
scsibus4 at softraid0: 256 targets
root on sd0a (cd6d9e34d180fed3.a) swap on sd0b dump on sd0b
fd0 at fdc0 drive 1: density unknown