linux-kernel - Re: [RFC PATCH 00/15] Prepare for new Intel family models

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Message-ID: <f97c1228-7fca-4487-814c-6dd6ba581721@citrix.com>
Date: Sat, 21 Dec 2024 00:29:10 +0000
From: Andrew Cooper <andrew.cooper3@...rix.com>
To: sohil.mehta@...el.com
Cc: acme@...nel.org, adrian.hunter@...el.com,
 alexander.shishkin@...ux.intel.com, bp@...en8.de,
 dave.hansen@...ux.intel.com, fenghua.yu@...el.com, hpa@...or.com,
 irogers@...gle.com, jdelvare@...e.com, jolsa@...nel.org,
 kan.liang@...ux.intel.com, lenb@...nel.org, linux-acpi@...r.kernel.org,
 linux-hwmon@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-perf-users@...r.kernel.org, linux-pm@...r.kernel.org,
 linux@...ck-us.net, luto@...nel.org, mark.rutland@....com, mingo@...hat.com,
 namhyung@...nel.org, peterz@...radead.org, rafael@...nel.org,
 rui.zhang@...el.com, tglx@...utronix.de, tony.luck@...el.com,
 viresh.kumar@...aro.org, x86@...nel.org
Subject: Re: [RFC PATCH 00/15] Prepare for new Intel family models

> ---Noteworthy quirks---
> Pentium II Overdrive - A unique family number:
>   Wikipedia says[2], In Intel's "Family/Model/Stepping" scheme, the Pentium II
>   OverDrive CPU identifies itself as family 6, model 3, though this is 
>   misleading, as it is not based on the family 6/model 3 Klamath core. As 
>   mentioned in the Pentium II Processor update documentation from Intel, 
>   "although this processor has a CPUID of 163xh, it uses a Pentium II processor 
>   CPUID 065xh processor core."
>
>   A dump of the microcode file 06-03-02 shows:
>     001/001: sig 0x00001632, pf_mask 0x00, 1998-06-10, rev 0x0002, size 2048
>   An archived CPUID dump [3] also says:
>     CPUID 00000001: 00001632-00000000-00000000-0183FBFF
>
>   That would translate to a family number of 22 (0x16). This aberration is 
>   not explicitly handled anywhere in the kernel so the platform might already 
>   be broken. This series might make it worse for the platform if the latest 
>   kernel works on it by chance.

Are you sure?  Bits 13:12 are the type field, and the 0x1 you've got is
for an OverDrive processor.

x86_family() will consider this to be family 6 as far as I can see.

~Andrew