linux-kernel - Re: [PATCH 13/15] x86/cpu: Make CONFIG_X86

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Message-ID: <8D770F85-5417-4A9E-80DE-1B6A890DECEF@zytor.com>
Date: Fri, 25 Apr 2025 08:15:39 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Arnd Bergmann <arnd@...nel.org>, Ingo Molnar <mingo@...nel.org>,
        linux-kernel@...r.kernel.org
CC: "Ahmed S . Darwish" <darwi@...utronix.de>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Ard Biesheuvel <ardb@...nel.org>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        John Ogness <john.ogness@...utronix.de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 13/15] x86/cpu: Make CONFIG_X86_CX8 unconditional

On April 25, 2025 5:10:27 AM PDT, Arnd Bergmann <arnd@...nel.org> wrote:
>On Fri, Apr 25, 2025, at 10:42, Ingo Molnar wrote:
>> @@ -257,7 +256,7 @@ config X86_MINIMUM_CPU_FAMILY
>>  	int
>>  	default "64" if X86_64
>>  	default "6" if X86_32 && (MPENTIUM4 || MPENTIUMM || MPENTIUMIII || 
>> MPENTIUMII || M686 || MVIAC3_2 || MVIAC7 || MEFFICEON || MATOM || MK7)
>> -	default "5" if X86_32 && X86_CX8
>> +	default "5" if X86_32
>>  	default "4"
>> 
>
>I just noticed this one: the final 'default "4"' is no longer possible
>here and can be removed. All the remaining CPUs report family "5" or
>higher.
>
>There is an old issue for some rare CPUs (Geode LX and Crusoe) that
>support CMOV but report family=6. These to boot a kernel with X86_MINIMUM_CPU_FAMILY=6 because it triggers the boot time check.
>
>     Arnd

They report family=5 because family=6 implies fcomi and nopl support (in the case of Crusoe, they have fcomi but didn't support movl.)