Further Cleaned-Up AMD Inception/SRSO Mitigation Code Ready Ahead Of Linux 6.6

It looks like the further-tuned AMD Inception / SRSO (Speculative Return Stack Overflow) mitigation code will be submitted for the upcoming Linux 6.6 merge window.

Beyond the recent AMD SRSO/Inception mitigation clean-ups, there has been a larger patch series with more fixes and clean-ups in the works and being iterated on the kernel mailing list. Among the fixes are also adjusting the behavior when mitigations=off or spec_rstack_overflow=off as the two means of run-time disabling the mitigation on affected processors. It's not expected that these new patches will impact the current mitigation overhead of the SRSO path, which can vary based on the AMD Zen CPU generation and presence of patched CPU microcode.

The news today is that these improved AMD SRSO Linux kernel patches have been picked up by TIP.git's x86/bugs branch. With it working its way into the tip.git area is effectively an indication it's now ready for mainlining to the Linux kernel.

With the patches though going into "x86/bugs" rather than "x86/urgent", it's an indication it is being staged for the imminent Linux 6.6 merge window rather than being treated as fixes for immediately pushing into the Linux 6.5 Git kernel this weekend. With Linux 6.5 stable due for release on Sunday, it makes sense to first push this code into Linux 6.6 Git and then potentially back-port to the Linux 6.5 stable series given that it would be limited time for testing prior to tagging v6.5.

In any event look for these AMD Inception/SRSO mitigation fixes to hit the mainline kernel soon now that they have been picked up by TIP.git. If you're not up to speed on the AMD Inception security vulnerability made public earlier this month, see my prior articles and benchmarks on AMD Inception.