linux-kernel - Re: [PATCH v1 10/12] tools/x86/kcpuid: Update bitfields to x86-cpuid-db v2.0

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Message-ID: <B5E71AD5-3AA3-4B2D-A832-D95F72454E0F@zytor.com>
Date: Fri, 07 Mar 2025 07:27:46 -0800
From: "H. Peter Anvin" <hpa@...or.com>
To: "Ahmed S. Darwish" <darwi@...utronix.de>
CC: Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Cooper <andrew.cooper3@...rix.com>, x86@...nel.org,
        John Ogness <john.ogness@...utronix.de>, x86-cpuid@...ts.linux.dev,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 10/12] tools/x86/kcpuid: Update bitfields to x86-cpuid-db v2.0

On March 7, 2025 7:07:04 AM PST, "Ahmed S. Darwish" <darwi@...utronix.de> wrote:
>On Thu, 06 Mar 2025, H. Peter Anvin wrote:
>>
>> Leaf 3h was not unique to Transmeta.
>>
>
>Thanks, I missed that Pentium III can provide leaf 0x3 as well.
>
>It seems that leaf 0x3's format differs between Intel and Transmeta.  On
>Intel, PSN is at ECX:EDX, while on Transmeta, the PSN is at EAX:EBX, and
>ECX:EDX on non-evaluation models provide the rest. [*]
>
>Unfortunately, so far, x86-cpuid-db does not support having a CPUID
>bitfield with different interpretations across vendors.
>
>Given that Linux force disables PSN at early boot, I'll just remove that
>leaf from the database — for now.  (Time wise, finishing the new
>linux/arch/x86/ CPUID data model for mainline submission is a much higher
>priority.)
>
>All the best,
>Ahmed
>
>[*] "Processor Recognition", Transmeta Corporation, 2002/05/07.

You can simply output the 128 bits as is. Some vendors will have zeroes in some of the fields, but it doesn't matter.