DragonFlyBSD Gets Fix To Be Able To Boot AMD Zen 2 Processors

Separate from the Linux boot issue affecting AMD Ryzen 3000 (Zen 2) processors that has been attributed to RdRand, DragonFlyBSD is the first BSD at least we've seen getting a separate fix to be able to boot these new AMD processors.

DragonFlyBSD lead developer Matthew Dillon who has been mesmerized by the AMD Threadripper performance for the past year now has his hands on new Zen 2 hardware. But it turns out the current DragonFlyBSD releases can't boot with these processors due to a separate problem from what we've seen on the Linux side.

He explained when landing the fix, "Issue load_fs() in the AP bootstrap. It appears that Zen 2 handles %fs in a weird way when the selector isn't loaded, causing the first wrmsr(MSR_FSBASE) to quietly fail, and possibly others too. For good measure, also issue load_ds() and load_es()."

The three-line patch is now present in DragonFlyBSD Git and thus allowing their latest daily images to hopefully boot fine on all new AMD Zen 2 systems. I'll have some Zen 2 + BSD benchmarks in due course.