'Friday Greg Kroah-Hartman released stable point releases of Linux
kernel 4.19.4, as well as 4.14.83 and 4.9.139. While they were basic
maintenance updates, the 4.19.4 and 4.14.83 releases are significant
because they also reverted the performance-killing Spectre patches
(involving "Single Thread Indirect Branch Predictors", or STIBP) that
had been back-ported from Linux 4.20, according to Phoronix:
There is improved STIBP code on the way for Linux 4.20 that by default
just applies STIBP to SECCOMP threads and processes requesting it via
prctl() but otherwise is off by default (that behavior can also be
changed via kernel parameters). Once that code is ready to go for
Linux 4.20, we may see it then back-ported to these stable trees.
Aside from reverting STIBP, these point releases just have various
fixes in them as noted for 4.19.4, 4.14.83, and 4.9.139.
Last Sunday Linus Torvalds complained that the performance impact of
the STIPB code "was clearly way more expensive than people were told,"
according to ZDNet:
"When performance goes down by 50 percent on some loads, people need
to start asking themselves whether it was worth it. It's apparently
better to just disable SMT entirely, which is what security-conscious
people do anyway," wrote Torvalds. "So why do that STIBP slow-down by
default when the people who *really* care already disabled SMT?"'
-- source: https://linux.slashdot.org/story/18/11/24/2320228
Dept. of Computer Science
University of Waikato, NZ
+64 (7) 858-5174