Public bug reported:
== Comment: #0 - Satheesh Rajendran - 2019-08-20 07:42:03 ==
---Problem Description---
cap-ibs=workaround defaults to "full software flush sequence" though "hardware
assisted flush" is available (kvm)
---uname output---
4.15.0-58-generic #64-Ubuntu
---Additional Hardware Info---
# lscpu
Architecture: ppc64le
Byte Order: Little Endian
CPU(s): 160
On-line CPU(s) list: 0-159
Thread(s) per core: 4
Core(s) per socket: 20
Socket(s): 2
NUMA node(s): 2
Model: 2.3 (pvr 004e 1203)
Model name: POWER9, altivec supported
CPU max MHz: 3800.0000
CPU min MHz: 2300.0000
L1d cache: 32K
L1i cache: 32K
L2 cache: 512K
L3 cache: 10240K
NUMA node0 CPU(s): 0-79
NUMA node8 CPU(s): 80-159
# lsmcode
Version of System Firmware :
Product Name : OpenPOWER Firmware
Product Version : witherspoon-OP9-v2.3-9.52
Product Extra : skiboot-v6.3-231-g0bf01d93ee39
Product Extra : bmc-firmware-version-2.07
Product Extra : occ-e5a2afd
Product Extra : hostboot-2b061c6
Product Extra : buildroot-2019.05-6-g0d430a2
Product Extra : capp-ucode-p9-dd2-v4
Product Extra : machine-xml-a6f4df3
Product Extra : hostboot-binaries-hw062819a.940
Product Extra : sbe-b96edc8
Product Extra : hcode-hw070319a.940
Product Extra : petitboot-v1.10.4
Product Extra : linux-5.1.16-openpower1-pecd2af3
# grep -H . /sys/devices/system/cpu/vulnerabilities/spectre_v2
/sys/devices/system/cpu/vulnerabilities/spectre_v2:Mitigation: Software count
cache flush (hardware accelerated)
Machine Type = power9 DD2.3 ppc64le
---Debugger---
A debugger is not configured
---Steps to Reproduce---
1. boot the guest with in above HW DD2.3 with cap-ibs=workaround(same
bydefault)
# kvm -M pseries-bionic-sxxm,cap-ibs=workaround -monitor stdio -vga none
-nographic -serial /dev/pts/0 -smp 8 -m 8192
/home/sath/ubuntu-18.04-ppc64le.qcow2
QEMU 2.11.1 monitor - type 'help' for more information
(qemu)
2. Check guest dmesg
#dmesg | grep cache-flush
[ 0.000000] count-cache-flush: full software flush sequence enabled.
Expected:
#dmesg | grep cache-flush
[ 0.000000] count-cache-flush: hardware assisted flush sequence enabled
Note: Hardware assisted flush is getting enabled if we set `cap-ccf-
assist` explicitly, like below
#kvm -M pseries-bionic-sxxm,cap-ibs=workaround,cap-ccf-assist=on -monitor stdio
-vnc none -nographic -serial /dev/pts/0 -smp 8 -m 8192
/home/sath/ubuntu-18.04-ppc64le.qcow2
QEMU 2.11.1 monitor - type 'help' for more information
(qemu)
#dmesg | grep cache-flush
[ 0.000000] count-cache-flush: hardware assisted flush sequence enabled
When hardware assisted flush capability is available it is good to enable
bydefault?
Userspace tool common name: Userspace tool common name: ii qemu-system-ppc
1:2.11+dfsg-1ubuntu7.18~ppa1 ppc64el QEMU
full system emulation binaries (ppc)
Qemu is from Bug 176932 comment 24
External:
https://bugs.launchpad.net/ubuntu/+source/qemu/+bug/1832622/comments/13
== Comment: #3 - Satheesh Rajendran - 2019-08-21 02:29:39 ==
(In reply to comment #2)
> Machine defaults can only be controlled on a per cpu basis, for example
> power7, power8, power9, etc.
> Since the hardware assisted flush is only available on POWER9 DD2.3 it can't
> be enabled by default for the entire power9 processor class. Thus it MUST
> default to the software workaround with the hardware flush enabled
> explicitly on the command line. This is to ensure migration compatibility
> between all power9 cpu models.
then it demands some ways to enable it above layers like libvirt etc.
Today we do not have any provision to do so apart from custom qemu
command-line, any thoughts on that?
how we expect the user to exploit this feature in KVM guest?,
It was initially suggested in libvirt to implement and got dropped
saying ` drop all features except for HTM, at least for the time being;`
, details here, https://www.redhat.com/archives/libvir-
list/2018-June/msg01655.html
any updates on reviving it, I know it is a libvirt component question,
but if there is any reason we can document it here and move this bug to
libvirt to get it fixed.
Regards,
-Satheesh
== Comment: #12 - Daniel Henrique Barboza - 2019-10-10 16:09:28 ==
The patches were accepted upstream:
https://github.com/libvirt/libvirt/commit/86a8e5a84cb6251748925163345c688e0ea794fa
https://github.com/libvirt/libvirt/commit/cab3ea2303617583f31ffb1a9fc73780f796dc06
https://github.com/libvirt/libvirt/commit/8958b47fabe122a8c1dac14198a07906158191c9
These patches will enable the ccf-assist to be used from Libvirt by using this
feature:
<features>
<ccf-assist state='on'/>
</features>
Remember: it is a feature Power 9 DD2.3+ only. Enabling it will break guest
migration if you migrate a guest with ccf-assist='on' it to a Power 9 DD2.2 or
older host.
Canonical: this feature will be rolled out in Libvirt version 5.9.0 at the end
of this month/start of November. I'll leave it at your own discretion how to
proceed here.
Thanks,
DHB
== Comment: #14 - Murilo Opsfelder Araujo - 2019-10-13 10:44:39 ==
Please mirror to Canonical to get patches from comment 12 back-ported to
Bionic, if that's Canonical's will.
** Affects: libvirt (Ubuntu)
Importance: Undecided
Assignee: Ubuntu on IBM Power Systems Bug Triage (ubuntu-power-triage)
Status: New
** Tags: architecture-ppc64le bugnameltc-180735 severity-medium
targetmilestone-inin---
** Tags added: architecture-ppc64le bugnameltc-180735 severity-medium
targetmilestone-inin---
** Changed in: ubuntu
Assignee: (unassigned) => Ubuntu on IBM Power Systems Bug Triage
(ubuntu-power-triage)
** Package changed: ubuntu => libvirt (Ubuntu)
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https://bugs.launchpad.net/bugs/1848229
Title:
[Power9][WSP][DD2.3] cap-ibs=workaround defaults to "full software
flush sequence" though "hardware assisted flush" is available
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