Re: [Qemu-devel] pseries-2.6 migration from QEMU-2.6 to QEMU-2.7 broken

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2016-09-22 at 12:32 +0200, Paolo Bonzini wrote:
> *However* a better fix would be to preserve the old flags for
> pseries-2.6, and only set the newer flags for pseries-2.7.  I'm not
> saying you have to do this, but if it's not hard (no idea) why not learn
> how to do it right.
> 
> The design is not stupid, it's just that compatibility is harder than
> you think and you are going through the same learning experiences that
> x86 went though.

Yeah well, the design is stupid inside target-ppc is what I meant in
the sense that it should have been clearer that those flags should not
have affected KVM, especially knowing that TCG still needed a lot of
work to add all the proper HV stuff.

Also most/all those flags concern instructions that are not relevant to
the "PAPR" mode which is running the guest with HV disabled, so
additionally, we might want to consider being smarter in the compare as
well to make sure that only the flags relevant to guest mode are
compared when the vCPU is in PAPR mode.

Cheers,
Ben.