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

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Message-ID: <CALCETrVToTrLQEbmXugja_Aif8LcZ7kX8Shu0Gg-FOx6w0p48A@mail.gmail.com>
Date:   Fri, 2 Oct 2020 10:15:04 -0700
From:   Andy Lutomirski <luto@...nel.org>
To:     "Chang S. Bae" <chang.seok.bae@...el.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>, Borislav Petkov <bp@...e.de>,
        Andrew Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        Len Brown <len.brown@...el.com>,
        Dave Hansen <dave.hansen@...el.com>, jing2.liu@...el.com,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>
Subject: Re: [RFC PATCH 22/22] x86/fpu/xstate: Introduce boot-parameters for
 control some state component support

On Thu, Oct 1, 2020 at 1:43 PM Chang S. Bae <chang.seok.bae@...el.com> wrote:
>
> "xstate.disable=0x6000" will disable AMX on a system that has AMX compiled
> into XFEATURE_MASK_USER_SUPPORTED.

Can we please use words for this?  Perhaps:

xstate.disable=amx,zmm

and maybe add a list in /proc/cpuinfo or somewhere in /proc or /sys
that shows all the currently enabled xsave states.

>
> "xstate.enable=0x6000" will enable AMX on a system that does NOT have AMX
> compiled into XFEATURE_MASK_USER_SUPPORTED (assuming the kernel is new
> enough to support this feature).

This sounds like it will be quite confusing to anyone reading the
kernel code to discover that a feature that is not "SUPPORTED" is
nonetheless enabled.