linux-kernel - Re: [PATCH] [RFC] x86/cpu: rework instruction set selection

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Message-ID: <49675319-D30C-417C-9BE6-20D2AB8E259A@zytor.com>
Date: Fri, 25 Apr 2025 13:15:24 -0700
From: "H. Peter Anvin" <hpa@...or.com>
To: Arnd Bergmann <arnd@...db.de>, Arnd Bergmann <arnd@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
CC: Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Alexander Usyskin <alexander.usyskin@...el.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mateusz Jończyk <mat.jonczyk@...pl>,
        Mike Rapoport <rppt@...nel.org>, Ard Biesheuvel <ardb@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] [RFC] x86/cpu: rework instruction set selection

On April 25, 2025 9:13:31 AM PDT, Arnd Bergmann <arnd@...db.de> wrote:
>On Fri, Apr 25, 2025, at 17:34, H. Peter Anvin wrote:
>> On April 25, 2025 7:15:15 AM PDT, Arnd Bergmann <arnd@...nel.org> wrote:
>>
>> I really don't like testing an unrelated feature (CMOV for PAE); 
>
>How about a new symbol with the opposite polarity, e.g. CONFIG_CPU_586?
>In that case, X86_HAVE_PAE and X86_CMOV could both depend on that
>not being set.
>
>I only picked the X86_CMOV symbol because it already exists in .config
>files, but that is not the important bit here.
>
>> furthermore, at least some old hypervisors were known to have
>> broken PAE.
>
>I'm not following. What does that have to do with my patch?
>
>     Arnd

This seems overly complex to me.