Here's an update.

The Xenial kernel doesn;t like the emulated POWER7 cpu that the command line being used generates by default.

processor       : 0
cpu             : POWER7 (raw), altivec supported
clock           : 1000.000000MHz
revision        : 2.3 (pvr 003f 0203)

timebase        : 512000000
platform        : pSeries
model           : IBM pSeries (emulated by qemu)
machine         : CHRP IBM pSeries (emulated by qemu)

We can boot a Wily image (kernel 4.2.0-35) just fine with the POWER7 cpu.


When booting Xenial's kernel with POWER7 cpu, it produces a stacktrace during module load:

[    9.885165] Loaded X.509 cert 'Build time autogenerated kernel key: 6687eed33bf99302166296c3e5cafe31ef38ad41'
[    9.886507] zswap: loaded using pool lzo/zbud
[    9.916000] modprobe[74]: unhandled signal 4 at 00003fffb5a4d03c nip 00003fffb5a4d03c lr 00003fffb5a25e24 code 30001
[    9.925819] modprobe[76]: unhandled signal 4 at 00003fff85b9d03c nip 00003fff85b9d03c lr 00003fff85b75e24 code 30001
[    9.928401] Key type trusted registered
[    9.930762] modprobe[79]: unhandled signal 4 at 00003fff7d05d03c nip 00003fff7d05d03c lr 00003fff7d035e24 code 30001
[    9.933360] modprobe[80]: unhandled signal 4 at 00003fff8820d03c nip 00003fff8820d03c lr 00003fff881e5e24 code 30001
[    9.936240] modprobe[83]: unhandled signal 4 at 00003fffb4fbd03c nip 00003fffb4fbd03c lr 00003fffb4f95e24 code 30001
[    9.938873] modprobe[84]: unhandled signal 4 at 00003fff92d4d03c nip 00003fff92d4d03c lr 00003fff92d25e24 code 30001
[    9.940335] Key type encrypted registered
[    9.940461] AppArmor: AppArmor sha1 policy hashing enabled
[    9.941005] ima: No TPM chip found, activating TPM-bypass!
[    9.942985] evm: HMAC attrs: 0x1
[    9.947081] hctosys: unable to open rtc device (rtc0)
[    9.987867] Freeing unused kernel memory: 6144K (c000000000ea0000 - c0000000014a0000)
[    9.991123] init[1]: unhandled signal 4 at 00003fff8edfd03c nip 00003fff8edfd03c lr 00003fff8edd5e24 code 30001
[    9.994581] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
[    9.994581] 
[    9.994889] CPU: 0 PID: 1 Comm: init Not tainted 4.4.0-18-generic #34-Ubuntu
[    9.995054] Call Trace:
[    9.995216] [c00000001e4c3a50] [c000000000aed6fc] dump_stack+0xb0/0xf0 (unreliable)
[    9.995336] [c00000001e4c3a90] [c000000000ae9930] panic+0x100/0x2c0
[    9.995398] [c00000001e4c3b20] [c0000000000bd554] do_exit+0xc24/0xc30
[    9.995443] [c00000001e4c3be0] [c0000000000bd644] do_group_exit+0x64/0x100
[    9.995490] [c00000001e4c3c20] [c0000000000ceaac] get_signal+0x55c/0x7b0
[    9.995534] [c00000001e4c3d10] [c000000000017424] do_signal+0x54/0x2b0
[    9.995578] [c00000001e4c3e00] [c00000000001787c] do_notify_resume+0xbc/0xd0
[    9.995677] [c00000001e4c3e30] [c000000000009838] ret_from_except_lite+0x64/0x68
[   10.011069] ---[ end Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000004
[   10.011069] 


When we use -enable-kvm, this bypasses the tcg POWER7 cpu, and uses the host cpu type (POWER8) which is why we can boot the Xenial kernel with KVM.

We need to open a linux task to help track down that issue; also if someone is testing Xenial on POWER7 hardware, that may help determine if there is a lurking qemu tcg issue, though given that Wily kernels boot fine in tcg mode; it's more likely there's something that changed/broke in the kernels since 4.2.0-35.

I'm marking the qemu task invalid, and will open the linux task.