linux-kernel - Re: [PATCH] x86/fpu: Parse comma separated list passed in clearcpuid

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Message-ID: <20190221134847.GQ32494@hirez.programming.kicks-ass.net>
Date:   Thu, 21 Feb 2019 14:48:47 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Prarit Bhargava <prarit@...hat.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Andi Kleen <ak@...ux.intel.com>,
        x86@...nel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] x86/fpu: Parse comma separated list passed in clearcpuid

On Thu, Feb 21, 2019 at 08:12:25AM -0500, Prarit Bhargava wrote:
> Users cannot disable multiple CPU features with the kernel parameter
> clearcpuid=.  For example, "clearcpuid=154 clearcpuid=227" only disables
> CPUID bit 154.
> 
> Previous to commit 0c2a3913d6f5 ("x86/fpu: Parse clearcpuid= as early XSAVE
> argument") it was possible to pass multiple clearcpuid options as kernel
> parameters using individual entries.  With the new code it isn't easy to
> replicate exactly that behaviour but a comma separated list can be easily
> implemented, eg) "clearcpuid=154,227"
> 
> Make the clearcpuid parse a comma-separated list of values instead of only
> a single value.

Can we also please kill the value thing entirely and only accept
strings. Having to reverse engineer the numbers is madness.

Also, wth would you want to disable XSAVE and EPB ?