Subject: a3b2cb30 broken panic reporting for qemu guests

From: David Gibson <[email-masked]>
Date: Wed, 29 Nov 2017 15:06:52 +1100

a3b2cb30 "powerpc: Do not call ppc_md.panic in fadump panic notifier"
purports to fix a problem when the kernel panics with fadump not
registered, but it breaks something else instead.  I _think_ it was
working on the incorrect assumption that ppc_md.panic was (or should
be) only used with fadump, but I'm not really sure.

Panic works with kdump enabled, and (I think) with fadump enabled).
However, with neither of these enabled, we always go to the generic
panic logic.

That's incorrect for PAPR guests - they should call ibm,os-term via
RTAS.  Under qemu this leads to a "GUEST_PANICKED" event notification
which higher-level management pays attention to.  Since a3b2cb30 we
now reboot instead of reporting that.

I believe it will also break panic for PS3 machines, but since that
platform basically no longer exists, we probably don't care.

I'm not entirely sure how to fix this.  I _think_ what we want is to
call ppc_md.panic from a late panic notifier, the way this patch does
for fadump_panic_event() if fadump is registered.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson