kvm_pr can't load on power9

[Christian Ehrhardt ]

Hi,
I have run into this and I'm not entirely sure if it is an error or just not supported.
I'll file the bug and would ask for a check and answer by the kernel Team and IBM about it.

On power you can never load the usual kvm_hv module in a guest.
 $ sudo modprobe kvm_hv
 modprobe: ERROR: could not insert 'kvm_hv': No such device

That is normal and expected.
But on a Power9 system I can neither load kvm_pr which was usually the way to go for nested KVM.

$ sudo modprobe kvm_pr
modprobe: ERROR: could not insert 'kvm_pr': Input/output error

There is no error whatsoever in dmesg when triggering this.
From libvirt the guest is defined with all defaults - see http://paste.ubuntu.com/p/2r34SG6pq6/

That gives the guest CPU this guest view:
cat /proc/cpuinfo
processor : 0
cpu : POWER9 (architected), altivec supported
clock : 2134.000000MHz
revision : 2.2 (pvr 004e 1202)

timebase : 512000000
platform : pSeries
model : IBM pSeries (emulated by qemu)
machine : CHRP IBM pSeries (emulated by qemu)
MMU : Radix

Nothing obvious here, also the module exists and seems normal to me:
$ modinfo kvm_pr
filename: /lib/modules/4.17.0-6-generic/kernel/arch/powerpc/kvm/kvm-pr.ko
alias: devname:kvm
alias: char-major-10-232
license: GPL
srcversion: 2472883ADEEBC51508B6BF4
depends: kvm
intree: Y
name: kvm_pr
vermagic: 4.17.0-6-generic SMP mod_unload mprofile-kernel relocatable
sig_id: PKCS#7
signer:
sig_key:
sig_hashalgo: md4
signature: 30:82...

Current kernel is From Cosmic (as that is what I test for atm): 4.17.0-6-generic

If I start the guest with the "least virtual" cpu via
  <cpu mode='host-passthrough' check='none'/>

I get no difference in /proc/cpuinfo from the guest nor does the problem change.

So is there a special constraint to Power9, is it the cosmic kernel, something else - would be great if there would be some advice on this.

[Christian Ehrhardt  (paelzer)]

This reminds me of a bug I filed actually - rereading history on the old one ...

[Christian Ehrhardt  (paelzer)]

Yeah, dup'ing