Two Linux Kernels Revert Performance-Killing Spectre Patches

[steven36]

Linux 4.19.4 & 4.14.83 Released With STIBP Code Dropped

 

 

On Friday marked the release of the Linux 4.19.4 kernel as well as 4.14.83 and 4.9.139.

Greg Kroah-Hartman issued this latest round of stable point releases as basic maintenance updates. While these point releases don't tend to be too notable and generally go unmentioned on Phoronix, this round is worth pointing out since 4.19.4 and 4.14.83 are the releases that end up reverting the STIBP behavior that applied Single Thread Indirect Branch Predictors to all processes on supported systems. That is what was introduced in Linux 4.20 and then back-ported to the 4.19/4.14 LTS branches, which in turn hurt the performance a lot. So for now the code is removed.

As covered yesterday, there is improved STIBP code on the way for Linux 4.20 that by default just apply 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.

 

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