Comment 50 for bug 1832622

Here is test #9 (#8 is the same as #4 from my previous tests. And not of much help since Disco-updates QEMU (v=1:3.1+dfsg-2ubuntu3.3) does not have cap-ibs=workaround):

*** 9- Bionic-proposed kernel + Disco-proposed QEMU
 $ uname -r; qemu-system-ppc64 --version | head -n 1
 4.15.0-60-generic
 QEMU emulator version 3.1.0 (Debian 1:3.1+dfsg-2ubuntu3.4)

 $ dmesg | grep count-cache
 [ 0.000000] count-cache-flush: hardware assisted flush sequence enabled

 $ qemu-system-ppc64 -machine pseries,? 2>&1 | grep "\|ibs\|ccf"
 cap-ibs=string (Indirect Branch Speculation (broken, workaround, fixed-ibs,fixed-ccd, fixed-na))
 cap-ccf-assist=bool (Count Cache Flush Assist via HW Instruction)

 - cap-ibs=broken
 $ dmesg | grep count-cache
 [ 0.000000] count-cache-flush: software flush disabled.

 - cap-ibs=workaround
 $ dmesg | grep count-cache
 [ 0.000000] count-cache-flush: full software flush sequence enabled.

 - cap-ibs=fixed-ccd
 qemu-system-ppc64: Requested safe indirect branch capability level not supported by kvm, try cap-ibs=workaround

 - cap-ibs=fixed-ibs
 qemu-system-ppc64: Requested safe indirect branch capability level not supported by kvm, try cap-ibs=workaround

 - cap-ccf-assist=off
 $ dmesg | grep count-cache
 [ 0.000000] count-cache-flush: software flush disabled.

 - cap-ccf-assist=on
 $ dmesg | grep count-cache
 [ 0.000000] count-cache-flush: software flush disabled.

 - cap-ibs=workaround,cap-ccf-assist=on
 $ dmesg | grep count-cache
 [ 0.000000] count-cache-flush: hardware assisted flush sequence enabled

 - cap-ibs=workaround,cap-ccf-assist=off
 $ dmesg | grep count-cache
 [ 0.000000] count-cache-flush: full software flush sequence enabled.

So my interpretation of the results is that the Disco kernel is indeed to blame for cap-ibs=workaround not working with QEMU 1:3.1+dfsg-2ubuntu3.4 and a DD 2.3 machine.