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

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Message-ID: <388fecd4-9b99-f405-fed4-1f6c3b53bc8b@redhat.com>
Date:   Wed, 27 Feb 2019 18:48:11 -0500
From:   Prarit Bhargava <prarit@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 2/21/19 8:48 AM, Peter Zijlstra wrote:
> 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 ?
> 

It looks like Fenghua has implemented this here:

https://marc.info/?l=linux-kernel&m=154908490105208&w=2

so please drop this patch.

Thanks,

P.