"While the Kernel Page Table Isolation (KPTI) patches were
quick to land in the mainline Linux kernel for addressing the Meltdown
CPU vulnerability, the "Retpoline" patches are still being worked on as
the leading approach on the Linux side for dealing with the Spectre CPU
vulnerability. The Retpoline patches are said to have little impact on
performance, but here are our benchmarks of these kernel patches for
seeing how they affect a variety of AMD and Intel systems."