Re: [Qemu-ppc] pseries on qemu-system-ppc64le crashes in doorbell_core_ipi()

[Suraj Jitindar Singh]

On Wed, 2019-03-27 at 17:51 +0100, Cédric Le Goater wrote:
> On 3/27/19 5:37 PM, Cédric Le Goater wrote:
> > On 3/27/19 1:36 PM, Sebastian Andrzej Siewior wrote:
> > > With qemu-system-ppc64le -machine pseries -smp 4 I get:
> > > 
> > > > #  chrt 1 hackbench
> > > > Running in process mode with 10 groups using 40 file
> > > > descriptors each (== 400 tasks)
> > > > Each sender will pass 100 messages of 100 bytes
> > > > Oops: Exception in kernel mode, sig: 4 [#1]
> > > > LE PAGE_SIZE=64K MMU=Hash PREEMPT SMP NR_CPUS=2048 NUMA pSeries
> > > > Modules linked in:
> > > > CPU: 0 PID: 629 Comm: hackbench Not tainted 5.1.0-rc2 #71
> > > > NIP:  c000000000046978 LR: c000000000046a38 CTR:
> > > > c0000000000b0150
> > > > REGS: c0000001fffeb8e0 TRAP: 0700   Not tainted  (5.1.0-rc2)
> > > > MSR:  8000000000089033 <SF,EE,ME,IR,DR,RI,LE>  CR:
> > > > 42000874  XER: 00000000
> > > > CFAR: c000000000046a34 IRQMASK: 1
> > > > GPR00: c0000000000b0170 c0000001fffebb70 c000000000a6ba00
> > > > 0000000028000000
> > > 
> > > …
> > > > NIP [c000000000046978] doorbell_core_ipi+0x28/0x30
> > > > LR [c000000000046a38] doorbell_try_core_ipi+0xb8/0xf0
> > > > Call Trace:
> > > > [c0000001fffebb70] [c0000001fffebba0] 0xc0000001fffebba0
> > > > (unreliable)
> > > > [c0000001fffebba0] [c0000000000b0170]
> > > > smp_pseries_cause_ipi+0x20/0x70
> > > > [c0000001fffebbd0] [c00000000004b02c]
> > > > arch_send_call_function_single_ipi+0x8c/0xa0
> > > > [c0000001fffebbf0] [c0000000001de600]
> > > > irq_work_queue_on+0xe0/0x130
> > > > [c0000001fffebc30] [c0000000001340c8]
> > > > rto_push_irq_work_func+0xc8/0x120
> > > 
> > > …
> > > > Instruction dump:
> > > > 60000000 60000000 3c4c00a2 384250b0 3d220009 392949c8 81290000
> > > > 3929ffff
> > > > 7d231838 7c0004ac 5463017e 64632800 <7c00191c> 4e800020
> > > > 3c4c00a2 38425080
> > > > ---[ end trace eb842b544538cbdf ]---
> > > 
> > > and I was wondering whether this is a qemu bug or the kernel is
> > > using an
> > > opcode it should rather not. If I skip doorbell_try_core_ipi() in
> > > smp_pseries_cause_ipi() then there is no crash. The comment says
> > > "POWER9
> > > should not use this handler" so…
> > 
> > I would say Linux is using a msgsndp instruction which is not
> > implemented
> > in QEMU TCG. But why have we started using dbells in Linux ? 

Yeah the kernel must have used msgsndp which isn't implemented for TCG
yet. We use doorbells in linux but only for threads which are on the
same core.
And when I try to construct a situation with more than 1 thread per
core (e.g. -smp 4,threads=4), I get "TCG cannot support more than 1
thread/core on a pseries machine".

So I wonder why the guest thinks it can use msgsndp...

> 
> ah. It seems arch_local_irq_restore() / replay_interrupt() generated
> some interrupt.
> 
> C.
>