Re: [Qemu-devel] [Qemu-ppc] ppc64 TCG emulation broken

[Alexander Graf <agraf@suse.de>]

On 09/29/2016 09:47 AM, David Gibson wrote:
> On Thu, Sep 29, 2016 at 12:41:04PM +0530, Bharata B Rao wrote:
>> Hi,
>>
>> I am observing a kernel crash with ppc64 TCG guest on x86 and git
>> bisect points to this commit:
>>
>> e7b1e06fbcb81ac66e2586214a6c42fdf15fadf3
>> [target-ppc: add vector insert instructions]
>>
>> I hit the following guest kernel panic during boot:
>>
>>           Starting Switch Root...
>> [   76.632260] systemd-journald[113]: Received SIGTERM from PID 1 (systemd).
>> [   77.082688] systemd-cgroups[1143]: unhandled signal 4 at
>> 00003fff85d3d718 nip 00003fff85d3d718 lr 00003fff85c8c274 code 30001
>> [   77.479368] systemd-coredum[1144]: unhandled signal 4 at
>> 00003fff948bd718 nip 00003fff948bd718 lr 00003fff9480c274 code 30001
>> [   77.479860] audit_printk_skb: 39 callbacks suppressed
>> [   77.479988] audit: type=1701 audit(1475132719.390:35):
>> auid=4294967295 uid=0 gid=0 ses=4294967295 subj=kernel pid=1144
>> comm="systemd-coredum" exe="/usr/lib/systemd/systemd-coredump" sig=4
>> [   77.485034] Process 1144(systemd-coredum) has RLIMIT_CORE set to 1
>> [   77.485156] Aborting core
>> [   77.858307] systemd[1]: unhandled signal 4 at 00003fff9a48d718 nip
>> 00003fff9a48d718 lr 00003fff9a3dc274 code 30001
>> [   77.858868] audit: type=1701 audit(1475132719.770:36):
>> auid=4294967295 uid=0 gid=0 ses=4294967295 subj=kernel pid=1
>> comm="systemd" exe="/usr/lib/systemd/systemd" sig=4
>> [   78.004191] systemd-coredum[1145]: unhandled signal 4 at
>> 00003fffa475d718 nip 00003fffa475d718 lr 00003fffa46ac274 code 30001
>> [   78.004648] audit: type=1701 audit(1475132719.910:37):
>> auid=4294967295 uid=0 gid=0 ses=4294967295 subj=kernel pid=1145
>> comm="systemd-coredum" exe="/usr/lib/systemd/systemd-coredump" sig=4
>> [   78.004971] Process 1145(systemd-coredum) has RLIMIT_CORE set to 1
>> [   78.005066] Aborting core
>> [   78.015142] Kernel panic - not syncing: Attempted to kill init!
>> exitcode=0x00000084
>> [   78.015142]
>> [   78.016926] CPU: 0 PID: 1 Comm: systemd Not tainted 4.6.4-301.fc24.ppc64 #1
>> [   78.017726] Call Trace:
>> [   78.019154] [c00000007e6638d0] [c0000000009df0f0]
>> .dump_stack+0xa8/0xe8 (unreliable)
>> [   78.022485] [c00000007e663960] [c0000000009dd6bc] .panic+0x12c/0x2fc
>> [   78.022631] [c00000007e663a00] [c0000000000cd6a8] .do_exit+0xca8/0xcb0
>> [   78.022735] [c00000007e663ae0] [c0000000000cd77c] .do_group_exit+0x5c/0xf0
>> [   78.022815] [c00000007e663b70] [c0000000000dd4ec] .get_signal+0x3bc/0x770
>> [   78.022918] [c00000007e663c70] [c00000000001761c] .do_signal+0x4c/0x2a0
>> [   78.023021] [c00000007e663db0] [c000000000017a4c] .do_notify_resume+0xac/0xc0
>> [   78.023411] [c00000007e663e30] [c000000000009944]
>> .ret_from_except_lite+0x70/0x74
>> [   78.077889] ---[ end Kernel panic - not syncing: Attempted to kill
>> init! exitcode=0x00000084
> Huh.  Well, that's unfortunate.  I don't imagine the guest is trying
> to use any of those new POWER9 instructions, so I guess we must have
> broken decode of one of the existing vector instructions with which it
> shares some part of the opcode.
>
> Any chance you could trace this and work out what instruction is
> giving the first illegal instruction exception?

... and whenever someone has some spare time, I would strongly advise 
for implementing RISU on PowerPC to catch these things before they happen ;)

   https://wiki.linaro.org/PeterMaydell/Risu


Alex