The "What If" Performance Cost To Kernel Page Table Isolation On AMD CPUs

Various real-world programs were showing at least a few percent impact when KPTI was enabled on the Ryzen 9 5900X desktop.

Much of the slowdowns stem from context switching taking significantly longer in the presence of Kernel Page Table Isolation.

Web browser performance with KPTI enabled on AMD CPUs can be a few percent slower.

That is the very quick overview of the Linux kernel's current Kernel Page Table Isolation (KPTI) performance on an AMD Ryzen 9 5900X desktop for reference purposes. But to reiterate, while the TU Graz security researchers have suggested otherwise, AMD's official security bulletin says no further mitigations are required at this time. Hopefully it stays that way and the Linux kernel PTI implementation proves unnecessary for AMD CPUs. If things change there is also the possibility of some enhanced or alternative approach that could alter the impact, so for now we'll just sum it up as the Ryzen 9 5900X performance overhead of "pti=on" for Linux 5.15.