The Linux Kernel Prepares For Larger AMD CPU Microcode Updates

Future AMD CPUs (more than likely, Zen 3) will be bearing larger CPU microcode sizes, resulting in the Linux kernel needing a change to load them.

Currently the AMD Linux CPU microcode handler has a static upper limit of the page size, which is generally 4K. But in preparation for "future AMD CPUs" that will exceed that size, that upper limit is being bumped.

With a change now pending as part of the x86/urgent work, that upper limit is being bumped to a factor of three times the page size. In other words, up to 12K microcode update size.

It will be interesting to see if they are tripling the limit for future-proofing and Zen 3 just crossing the existing threshold slightly or if some fundamental change/addition in Zen 3 is leading to much larger microcode updates for AMD CPUs moving forward.

That patch is also being called for back-porting back through to the Linux 4.14 LTS days with CPU microcode updating being important particularly these days, though generally for other aspects of AMD Zen 3 support it's like with all new hardware: the newer the Linux kernel, likely the better the support experience and performance. In recent months AMD has begun sending out a lot more patches for AMD Family 19h / Zen 3 plumbing to the Linux kernel ahead of the first of those CPUs expected later this calendar year.