Workarounds To Get AMD Zen/Ryzen CPUs Running Solid On FreeBSD

While the Linux support for AMD Ryzen/EPYC processors has been solid on Linux now largely the past number of months with just some exceptions like Raven Ridge display issues, the FreeBSD support has been a bit more choppy.

The number of AMD Zen + FreeBSD issues has gone down in recent months when using the latest FreeBSD code, but some have still talked of stability issues that can creep up over time.

AMD though recently made public their errata and workarounds for Zen CPUs. FreeBSD contributor Konstantin Belousov posted earlier this month a small script making use of FreeBSD's cpucontrol utility for changing some MSRs based upon the errata documentation. That script can be found here and there is also the public AMD Revision Guide for AMD Family 17h.

It's looking good that those latest tweaks are causing FreeBSD to run stable on previously problematic Ryzen hardware. Ultimately they will be incorporating these changes into the FreeBSD kernel once receiving sufficient feedback to verify correct behavior.