linux-kernel - Re: [RFC PATCH] Use feature bit names in clearcpuid=

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Message-ID: <87mu1ib5mw.fsf@nanos.tec.linutronix.de>
Date:   Tue, 22 Sep 2020 10:03:03 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Borislav Petkov <bp@...en8.de>, x86-ml <x86@...nel.org>
Cc:     lkml <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] Use feature bit names in clearcpuid=

On Sun, Sep 20 2020 at 17:42, Borislav Petkov wrote:
> Hi,
>
> so tglx hates this clearcpuid= interface where you have to give the
> X86_FEATURE array indices in order to disable a feature bit for testing.
> Below is a first attempt (lightly tested in a VM only) to accept the bit
> names from /proc/cpuinfo too.
>
> I say "too" because not all feature bits have names and we would still
> have to support the numbers. Yeah, yuck.
>
> An exemplary cmdline would then be something like:
>
> clearcpuid=de,440,smca,succory,bmi1,3dnow ("succory" is wrong on
> purpose).
>
> and it says:
>
> [    0.000000] Clearing CPUID bits: de 13:24 smca bmi1 3dnow
>
> Also, I'm thinking we should taint the kernel when this option is used.
>
> Thoughts?

Yes, instead of making it differently horrible, can we finally remove that
nonsense which should have never been there in the first place?

Thanks,

        tglx