qemu-system-s390x fails when running without kvm: fatal: EXECUTE on instruction prefix 0x7f4 not implemented

[Liang Yan]

just wondering if TCG implements instruction prefix 0x7f4

server3:~ # zcat /boot/vmlinux-4.4.162-94.72-default.gz > /tmp/kernel

--> starting qemu with kvm enabled works fine
server3:~ # qemu-system-s390x -nographic -kernel /tmp/kernel -initrd /boot/initrd -enable-kvm
Initializing cgroup subsys cpuset
Initializing cgroup subsys cpu
Initializing cgroup subsys cpuacct
Linux version 4.4.162-94.72-default (geeko@buildhost) (gcc version 4.8.5 (SUSE Linux) ) #1 SMP Mon Nov 12 18:57:45 UTC 2018 (9de753f)
setup.289988: Linux is running under KVM in 64-bit mode
setup.b050d0: The maximum memory size is 128MB
numa.196305: NUMA mode: plain
Write protected kernel read-only data: 8692k
[...]

--> but starting qemu without kvm enabled works fails
server3:~ # qemu-system-s390x -nographic -kernel /tmp/kernel -initrd /boot/initrd
qemu: fatal: EXECUTE on instruction prefix 0x7f4 not implemented

PSW=mask 0000000180000000 addr 000000000067ed6e cc 00
R00=0000000080000000 R01=000000000067ed76 R02=0000000000000000 R03=0000000000000000
R04=0000000000111548 R05=0000000000000000 R06=0000000000000000 R07=0000000000000000
R08=00000000000100f6 R09=0000000000000000 R10=0000000000000000 R11=0000000000000000
R12=0000000000ae2000 R13=0000000000681978 R14=0000000000111548 R15=000000000000bef0
F00=0000000000000000 F01=0000000000000000 F02=0000000000000000 F03=0000000000000000
F04=0000000000000000 F05=0000000000000000 F06=0000000000000000 F07=0000000000000000
F08=0000000000000000 F09=0000000000000000 F10=0000000000000000 F11=0000000000000000
F12=0000000000000000 F13=0000000000000000 F14=0000000000000000 F15=0000000000000000
V00=00000000000000000000000000000000 V01=00000000000000000000000000000000
V02=00000000000000000000000000000000 V03=00000000000000000000000000000000
V04=00000000000000000000000000000000 V05=00000000000000000000000000000000
V06=00000000000000000000000000000000 V07=00000000000000000000000000000000
V08=00000000000000000000000000000000 V09=00000000000000000000000000000000
V10=00000000000000000000000000000000 V11=00000000000000000000000000000000
V12=00000000000000000000000000000000 V13=00000000000000000000000000000000
V14=00000000000000000000000000000000 V15=00000000000000000000000000000000
V16=00000000000000000000000000000000 V17=00000000000000000000000000000000
V18=00000000000000000000000000000000 V19=00000000000000000000000000000000
V20=00000000000000000000000000000000 V21=00000000000000000000000000000000
V22=00000000000000000000000000000000 V23=00000000000000000000000000000000
V24=00000000000000000000000000000000 V25=00000000000000000000000000000000
V26=00000000000000000000000000000000 V27=00000000000000000000000000000000
V28=00000000000000000000000000000000 V29=00000000000000000000000000000000
V30=00000000000000000000000000000000 V31=00000000000000000000000000000000
C00=0000000000000000 C01=0000000000000000 C02=0000000000000000 C03=0000000000000000
C04=0000000000000000 C05=0000000000000000 C06=0000000000000000 C07=0000000000000000
C08=0000000000000000 C09=0000000000000000 C10=0000000000000000 C11=0000000000000000
C12=0000000000000000 C13=0000000000000000 C14=0000000000000000 C15=0000000000000000

Aborted (core dumped)

server3:~ # lscpu
Architecture: s390x
CPU op-mode(s): 32-bit, 64-bit
Byte Order: Big Endian
CPU(s): 2
On-line CPU(s) list: 0,1
Thread(s) per core: 1
Core(s) per socket: 1
Socket(s) per book: 1
Book(s) per drawer: 1
Drawer(s): 2
NUMA node(s): 1
Vendor ID: IBM/S390
Machine type: 2964
BogoMIPS: 20325.00
Hypervisor: z/VM 6.4.0
Hypervisor vendor: IBM
Virtualization type: full
Dispatching mode: horizontal
L1d cache: 128K
L1i cache: 96K
L2d cache: 2048K
L2i cache: 2048K
L3 cache: 65536K
L4 cache: 491520K
NUMA node0 CPU(s): 0-63
Flags: esan3 zarch stfle msa ldisp eimm dfp edat etf3eh highgprs te vx sie
server3:~ # uname -a
Linux server3 4.4.126-94.22-default #1 SMP Wed Apr 11 07:45:03 UTC 2018 (9649989) s390x s390x s390x GNU/Linux
server3:~ #

[Thomas Huth (th-huth)]

Which version of QEMU are you using here? I think this should be working fine with the latest version of QEMU (>= v2.10).

[Liang Yan (lyanux)]

Hi, Thomas, you are right, I am using 2.9.1, and it does look OK in 2.10. do you mind to point me which part of code fixed it? Thanks.

[Liang Yan (lyanux)]

A little bit confused here, I tired to bisect it from 2.10, but it was always good from this branch. then I went back to 2.9.1, it was always crashed. Machine type related?

[Thomas Huth (th-huth)]

This should be the commit that fixed this issue:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=303c681a8f50eb88fbafc

[Liang Yan (lyanux)]

Confirmed the fix, thanks for the help.