Messages in this thread | | | Date | Fri, 29 Mar 2024 12:40:07 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH 01/74] x86/cpu/vfm: Add/initialize x86_vfm field to struct cpuinfo_x86 |
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On Thu, Mar 28, 2024 at 06:32:35PM +0000, Luck, Tony wrote: > I don't think the format is really that big an issue. Including stepping in the > format adds complexity to a thousand places these checks are made while > only being useful in a few dozen.
I've figured out what the problem is with steppings - ranges. If you have a range of steppings which all belong to the same model, then you have to complicate the checks by either masking out the stepping or use the X86_STEPPING_ANY thing which forces you to use x86_match_cpu() instead of a simple integer comparison.
And you should talk to your folks what their plan is for the new families because if they do a range of model numbers which all belong to the same CPU model like AMD does, then your simple comparison scheme goes out the window because it can't really deal with ranges.
Because from looking at your set, I don't see a slick way to check whether a concrete f/m/s tuple belongs to a range without involved checking.
For example, models:
case 0x30 ... 0x4f: case 0x60 ... 0x7f: case 0x90 ... 0x91: case 0xa0 ... 0xaf:
are all Zen2. I could do a X86_MATCH_VF_MODEL_RANGE and we even had a patch like that at some point but it didn't go in. But even if I did that, I'd still need to do x86_match_cpu() instead of the current X86_FEATURE_ZEN* checks we're doing.
So I don't think I can switch AMD to use that. It looks like the 'V' in "VFM" could just as well turn into "I".
:-)
I'd say.
-- Regards/Gruss, Boris.
https://people.kernel.org/tglx/notes-about-netiquette
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