On 2019-03-29 16:20:51 [+1100], Suraj Jitindar Singh wrote:

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.

It is msgsndp as per instruction decode.

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...

I see
|# cat /sys/devices/system/cpu/cpu*/topology/thread_siblings_list
|0
|1
|2
|3

so this works all well. The problem is when a CPU sends an IPI to itself
then linux's doorbell_try_core_ipi() considers this as a valid sibling
and here we have the msgsndp.

Sebastian