linux-kernel - Re: [PATCH v4 22/22] x86/fpu/xstate: Introduce boot-parameters to control state component support

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Date:   Fri, 26 Mar 2021 20:22:49 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Len Brown <lenb@...nel.org>, Dave Hansen <dave.hansen@...el.com>
Cc:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, X86 ML <x86@...nel.org>,
        "Brown\, Len" <len.brown@...el.com>,
        "Liu\, Jing2" <jing2.liu@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Documentation List <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v4 22/22] x86/fpu/xstate: Introduce boot-parameters to control state component support

Len,

On Fri, Mar 26 2021 at 11:27, Len Brown wrote:
> On Thu, Mar 25, 2021 at 7:10 PM Dave Hansen <dave.hansen@...el.com> wrote:
>> From some IRC chats with Thomaas and Andy, I think it's safe to say that
>> they're not comfortable blindly enabling even our "simple features".  I
>> think we're going to need at least some additional architecture to get
>> us to a point where everyone will be comfortable.
>
> There is no code in this patch series, including patch 22, that enables
> an unvalidated feature by default.
>
> Yes, I fully accept that patch 22 allows a user to enable something
> that a distro didn't validate.

That's not the point. And neither Andy nor myself asked for distros to
validate and approve anything.

> If there is a new requirement that the kernel cmdline not allow anything
> that a distro didn't explicitly validate, then about 99.9% of the kernel cmdline
> options that exist today would need to be removed.
>
> Does such a requirement exist, or does it not?

Nobody said that, but patches to remove command line options are always
welcome. Can we start with the most horrible of all we have today, i.e
"clearcpuid=", please?

Thanks,

        tglx