On Sun, Aug 29, 2021 at 04:09:54AM +0000, Joseph wrote:
Hi Mark, Cédric, Greg at the openbsd-ppc ML,
It is great to talk to you. Thank you for taking on the conversation.
Right, OpenBSD implements powernv meaning it runs on bare metal on
Power9, that is great.
What I wanted to ask about with this thread is:
To have the same utility of Power9 as of AMD64, it would be great to
have a high speed virtualizer, like what OpenBSD's VMM or Linux' KVM-
QEMU accomplish on AMD64.
Linux KVM-QEMU supports Power9 already so that's a great start: One
runs Linux powernv bare metal on Power9 hardware. Each VM is a
KVM-QEMU instance.
Is there any way today to make Linux-KVM-QEMU as VM host run
OpenBSD as a high speed (say >90% of bare metal performance, here
presume KVM uses PCIe passthrough) VM guest -
I'm afraid this is more or less impossible, without adding
PAPR/pseries support to OpenBSD. The fundamental problem is that the
virtualization facilities on the POWER chip don't really allow
efficient full hardware virtualization, only para-virtualization and
PAPR is that para-virtualized environment.
That's why the "powernv" machine type doesn't utilize KVM and is fully
emulated and therefore slow. It might be possible to use the
"powernv" machine type with the "PR" implementation of KVM - that's a
KVM implementation which works by running the entire guest in
userspace and emulating all privileged instructions. But:
* KVM PR doesn't currently work properly on POWER9, and getting it
working would be a significant amount of work
* The way KVM PR works means it's very fiddly to get right, so it's
unlikely to ever be suitable for production work
* Depending on host and guest cpu models there might be a few corner
cases it can never get exactly right