AMD CPU Microcode Fix For Linux To Patch Every Logical Thread Nears Mainline

[phoronix]

Phoronix: AMD CPU Microcode Fix For Linux To Patch Every Logical Thread Nears Mainline

Back in August I wrote about a patch to change AMD's CPU microcode loading on Linux to now patch every logical CPU thread rather than just per physical core. It turned out that at least some CPU microcode updates do make per-threasd modifications while the Linux kernel microcode handling for AMD was just applying microcode updates at run-time on a per-core basis. That patch was seemingly forgotten about but has now been queued up as part of x86 "urgent" changes for the mainline kernel...

https://www.phoronix.com/news/AMD-CPU-Microcode-Per-Thread

[tildearrow]

Typo:

It turned out that at least some CPU microcode updates do make per-threasd modifications

[linuxgeex]

This is particularly interesting to me from Zen4 perspective. Do Zen4 CPUs run faster with kernel mitigations disabled or enabled when microcode mitigations are/are not loaded?

[quaz0r]

does hyperthreading even make sense any more? seems like a hacky kludge someone came up with before processors had much more than one or a couple cores, and now we are seemingly stuck carrying it forward forever because why again?

[smitty3268]

does hyperthreading even make sense any more? seems like a hacky kludge someone came up with before processors had much more than one or a couple cores, and now we are seemingly stuck carrying it forward forever because why again?

It's incredibly cost-efficient for certain server applications which get big boosts for a very minor increase in silicon. I think for a desktop design I'd agree it's not worth it, but AMD and Intel are attempting to share the same architecture across epyc/xeon down to laptops.