Hello.
Yes, Mr. Kamal Mostafa is right. Linux kernel v4.4.0-123.147 will
contain a fix for all of these issues with, for example,
'/var/log/syslog' flooding with 'ibrs_dump', 'use_ibrs/ibpb' and
'sysctl_ibrs{,ibpb}_enabled' entries. Now, a "proposed" kernel is
v4.4.0-122.146 with a fix for "Redpine: WiFi scan stopping issue
observed with BLE (LP: #1757435)".
Anyway, next kernel version, mentioned above will be updated, at last,
to the v4.4.128 stable release (current version, available e.g. in 16.04
LTS is v4.4.117) and will contain this patch, of course:
* ibrs/ibpb fixes result in excessive kernel logging (LP: #1755627)
- SAUCE: remove ibrs_dump sysctl interface
So, we have to wait a little more, because so-called "master-next"
branch (with all needed patches for already mentioned v4.4.128 Stable
release) was updated only 24 hours ago. Additionally, there will be also
a couple of 'x86/spectre' and 'x86/retpoline' patches (mainly in
v4.4.118).
Thanks, best regards.
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https://bugs.launchpad.net/bugs/1755627
Title:
ibrs/ibpb fixes result in excessive kernel logging
Status in linux package in Ubuntu:
Fix Committed
Status in linux source package in Trusty:
Fix Committed
Status in linux source package in Xenial:
Fix Committed
Status in linux source package in Artful:
Fix Committed
Bug description:
Since at least kernel 4.4.0-116, every invocation of `sysctl -a`
results in kernel logs similar to the following:
% sysctl -a &>/dev/null; dmesg -T | tail -8
[Wed Mar 14 00:06:36 2018] sysctl_ibrs_enabled = 0, sysctl_ibpb_enabled = 0
[Wed Mar 14 00:06:36 2018] use_ibrs = 4, use_ibpb = 4
[Wed Mar 14 00:06:36 2018] read cpu 0 ibrs val 0
[Wed Mar 14 00:06:36 2018] read cpu 1 ibrs val 0
[Wed Mar 14 00:06:36 2018] sysctl_ibrs_enabled = 0, sysctl_ibpb_enabled = 0
[Wed Mar 14 00:06:36 2018] use_ibrs = 4, use_ibpb = 4
[Wed Mar 14 00:06:36 2018] read cpu 0 ibrs val 0
[Wed Mar 14 00:06:36 2018] read cpu 1 ibrs val 0
The output varies with the number of CPUs.
After digging a bit, it turns out this is triggered upon every read of
`kernel.ibrs_dump`:
% for i in {1..3}; do sysctl kernel.ibrs_dump; dmesg -T | tail -8; echo;
sleep 1; done
kernel.ibrs_dump = 0
[Wed Mar 14 00:08:48 2018] sysctl_ibrs_enabled = 0, sysctl_ibpb_enabled = 0
[Wed Mar 14 00:08:48 2018] use_ibrs = 4, use_ibpb = 4
[Wed Mar 14 00:08:48 2018] read cpu 0 ibrs val 0
[Wed Mar 14 00:08:48 2018] read cpu 1 ibrs val 0
[Wed Mar 14 00:08:48 2018] sysctl_ibrs_enabled = 0, sysctl_ibpb_enabled = 0
[Wed Mar 14 00:08:48 2018] use_ibrs = 4, use_ibpb = 4
[Wed Mar 14 00:08:48 2018] read cpu 0 ibrs val 0
[Wed Mar 14 00:08:48 2018] read cpu 1 ibrs val 0
kernel.ibrs_dump = 0
[Wed Mar 14 00:08:49 2018] sysctl_ibrs_enabled = 0, sysctl_ibpb_enabled = 0
[Wed Mar 14 00:08:49 2018] use_ibrs = 4, use_ibpb = 4
[Wed Mar 14 00:08:49 2018] read cpu 0 ibrs val 0
[Wed Mar 14 00:08:49 2018] read cpu 1 ibrs val 0
[Wed Mar 14 00:08:49 2018] sysctl_ibrs_enabled = 0, sysctl_ibpb_enabled = 0
[Wed Mar 14 00:08:49 2018] use_ibrs = 4, use_ibpb = 4
[Wed Mar 14 00:08:49 2018] read cpu 0 ibrs val 0
[Wed Mar 14 00:08:49 2018] read cpu 1 ibrs val 0
kernel.ibrs_dump = 0
[Wed Mar 14 00:08:50 2018] sysctl_ibrs_enabled = 0, sysctl_ibpb_enabled = 0
[Wed Mar 14 00:08:50 2018] use_ibrs = 4, use_ibpb = 4
[Wed Mar 14 00:08:50 2018] read cpu 0 ibrs val 0
[Wed Mar 14 00:08:50 2018] read cpu 1 ibrs val 0
[Wed Mar 14 00:08:50 2018] sysctl_ibrs_enabled = 0, sysctl_ibpb_enabled = 0
[Wed Mar 14 00:08:50 2018] use_ibrs = 4, use_ibpb = 4
[Wed Mar 14 00:08:50 2018] read cpu 0 ibrs val 0
[Wed Mar 14 00:08:50 2018] read cpu 1 ibrs val 0
Those tests were against an EC2 instance running Ubuntu 4.4.0-116.140-generic
4.4.98 per /proc/version_signature
Normally this would not be the biggest concern but we have tooling
that gathers instance info on a schedule, including sysctl output,
thus resulting in the kernel ring buffer being full of nothing but
said output in most cases and hindering live troubleshooting as a
result.
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