23 Sep
2022
23 Sep
'22
7:57 a.m.
On Thu, Sep 22, 2022 at 02:21:31PM -0700, Dave Hansen wrote:
FWIW, I'd much rather do something like
if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD) && (boot_cpu_data.x86_model >= 0xF)) return;
inl(slow_whatever);
than a Zen check. AMD has, as far as I know, been a lot more sequential and sane about model numbers than Intel, and there are some AMD model number range checks in the codebase today.
Some might be broken; apparently their SoC/Entertainment divisions has a few out of order SKUs that were not listed in their regular documents. (yay interweb)
I ran into this when I tried doing a Zen2 range check for retbleed. In the end we ended up using the availablility of STIBP as a heuristic to indentify Zen2+ or something.