Re: QEMU-KVM offers OPAL firmware interface? OpenBSD guest support?

[Greg Kurz]

On Fri, 27 Aug 2021 18:48:04 +0200
Mark Kettenis <mark.kettenis@xs4all.nl> wrote:

> > Date: Fri, 27 Aug 2021 18:02:59 +0200
> > From: Greg Kurz <groug@kaod.org>
> > 
> > On Fri, 27 Aug 2021 15:12:31 +0000
> > Joseph <joseph.mayer@protonmail.com> wrote:
> > 
> > > On Friday, August 27th, 2021 at 11:01 PM, Greg Kurz <groug@kaod.org> 
> > > wrote:
> > > > Linux knows how to drive both powernv and pseries platforms.
> > > ..
> > > > OpenBSD might have to implement proper guest-side pseries
> > > > support to run as a guest under an hypervisor on POWER. I don't
> > > > know OpenBSD but this likely a huge effort.
> > > >
> > > > More details in the "Linux on POWER Architecture Reference":
> > > > https://openpowerfoundation.org/wp-content/uploads/2020/07/LoPAR-20200611.pdf
> > > > and under the arch/powerpc/platforms/pseries/ directory in the linux
> > > > kernel sources.
> > > 
> > > Hi Greg,
> > > 
> > > Thanks for following up.
> > > 
> > > (Meanwhile I posted this Q to KVM-PPC and QEMU-PPC too. On the latter 
> > > it's https://lists.nongnu.org/archive/html/qemu-ppc/2021-08/msg00416.html 
> > > and on the further it didn't register yet.)
> > > 
> > > First I believe KVM-QEMU and "PowerKVM" are different - the latter was
> > > a KVM fork maintained by IBM. The further is just the KVM and QEMU
> > > repo. Did IBM their contributions so PowerKVM was upstreamed, you tell
> > > me.
> > > 
> > 
> > Yes you're right that PowerKVM was an IBM internal fork of KVM and
> > QEMU, but it was discontinued ages ago. All the relevant bits have
> > been merged upstream and all development since then happens upstream.
> > So it doesn't make a big difference now to use PowerKVM instead of
> > QEMU-KVM on POWER.
> > 
> > > Are you saying that KVM-QEMU has all relevant Power9 support
> > > already, for a Linux host OpenBSD as a guest on bare metal
> > > ("powernv" mode)?
> > > 
> > 
> > There's some confusion here. In bare metal, you just have a single
> > instance of the OS running unvirtualized directly on the host.
> > KVM-QEMU isn't involved at all in this case. According to the OpenBSD
> > statement, you can already install and run it in this mode on an
> > OpenPOWER system.
> 
> Correct.
> 
> > > In this case why would there be any relevance in OpenBSD implementing
> > > pseries.
> > > 
> > 
> > If you want to also run OpenBSD inside a VM, then OpenBSD must
> > implement proper support to be able to run in the paravirtualized
> > PAPR environment provided by KVM-QEMU on POWER. The OpenBSD statement
> > seem to indicate this is missing. Nothing special "should" be needed
> > on the KVM-QEMU side.
> 
> Indeed.  OpenBSD/powerpc64 currently does not implement PAPR
> environment support.  I've looked at it at some point and I don't
> think adding support for it would be impossible.  But I only have
> powernv hardware.  I suppose I could run KVM-QEMU on Linux on that but
> my time is limited.
> 

Yeah, KVM-QEMU can run on powernv hardware. So you could use it
as a development environment to implement PAPR support in OpenBSD.
This is clearly not something achievable if you only have limited
time though.

> It is possible to use QEMU to emulate a powernv machine and in
> principle you can run OpenBSD in that environment on a Linux host.
> But that's emulation and not virtualization.

Yeah, no KVM in this case and it will be extremely slow.

>  It doesn't seem to work
> though and the installer hangs after printing its first message.  I
> suspect QEMU's emulation of the XIVE interrupt controller isn't 100%
> faithful.  It's also really slow when running on an amd64 machine, so
> I didn't investigate further.

A lot of things can go wrong when it comes to boot a powernv platform :)

Cc'ing Cedric who is the maintainer of XIVE and POWERNV in QEMU.

Cheers,

--
Greg