linux-kernel - Re: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid

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Message-ID: <9fa7406b-113f-fe0a-9fc7-ef00b3a6b620@intel.com>
Date:   Mon, 4 Feb 2019 11:05:52 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Fenghua Yu <fenghua.yu@...el.com>
Cc:     Ingo Molnar <mingo@...hat.com>, H Peter Anvin <hpa@...or.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Michael Chan <michael.chan@...adcom.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v3 08/10] x86/setcpuid: Add kernel option setcpuid

On 2/4/19 9:49 AM, Thomas Gleixner wrote:
> On Fri, 1 Feb 2019, Fenghua Yu wrote:
>> This option behaves like existing kernel option clearcpuid.
> 
> No it does NOT. clearcpuid allows to disable things.
> 
> This allows to enable random CPUID bits without any sanity checking. Not
> going to happen. We made it clear in the past that functionality needs to
> be detectable by enumeration. We do quirks for broken crap, but this is
> just not how it works.

Hi Thomas,

I think we are trying persuade you like mentioned here:

> http://lkml.kernel.org/r/alpine.DEB.2.21.1807122153170.1597@nanos.tec.linutronix.de

But, we're not being very persuasive because we kinda forgot about the
"if and only if" condition that you mentioned.