Comment 84 for bug 1690085

The microcode updates AMD had announced https://www.amd.com/en/corporate/security-updates are going to be availble to AMD customers "by downloading BIOS updates provided by PC and server manufacturers and motherboard providers" are now actually available as separate microcode packages which can be loaded by the OS during early boot.

For now, the microcode has not undergone sufficient testing on Ubuntu's end so it is only made available on the ubuntu-security-proposed PPA (so far, this will change if it looks fine).

A changelog for the upstream (Debian) package is available at https://launchpad.net/debian/+source/amd64-microcode/+changelog - according to a member of the Ubuntu security team it primarily (not sure if exclusively?) targets family 17h (Zen, so Ryzen, Epyc, Threadripper) processors.

Note that Ubuntu 14.04 systems running Linux 3.13 require a kernel patch for this microcode to work properly.

I do not know whether or not this microcode update provides mitigations for the bug discussed here (it might have helped for AMD to state so), but it is probably worth a try if your mainboard vendor has not provided a recent enough BIOS upgrade (and your system remains unstable) or the latest BIOS update you have just doesn't mitigate Spectre v2 in hardware, yet.