linux-kernel - Re: [PATCH 1/1] x86/fpu: Allow clearcpuid= to clear several bits

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Date:   Wed, 22 Apr 2020 18:41:37 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     John Haxby <john.haxby@...cle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
        x86@...nel.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH 1/1] x86/fpu: Allow clearcpuid= to clear several bits

> 
> I did wonder about that.   However, cmdline_find_option() is specifically documented as 
> 
>  * Find a non-boolean option (i.e. option=argument). In accordance with
>  * standard Linux practice, if this option is repeated, this returns the
>  * last instance on the command line.

Okay so would need a special version that uses the first and an option
to pass the cmdline string.

> 
> And since that appeared in 2017 I decided to stick with the new-fangled interface :)   This is a little-used feature; I'm not sure it's worth the effort of parsing the command line for the old style.  What do you think?

I'm not sure it's that little used.  We use it quite a bit for testing
and workarounds, and it might be that some of those are deployed.

-Andi