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Date:   Thu, 19 Nov 2020 21:02:26 -0800
From:   Andy Lutomirski <>
To:     "Chang S. Bae" <>
Cc:     Thomas Gleixner <>,
        Ingo Molnar <>, Borislav Petkov <>,
        Andrew Lutomirski <>, X86 ML <>,
        Len Brown <>,
        Dave Hansen <>,
        "Liu, Jing2" <>,
        "Ravi V. Shankar" <>,
        LKML <>,
        "open list:DOCUMENTATION" <>
Subject: Re: [PATCH v2 22/22] x86/fpu/xstate: Introduce boot-parameters for
 control some state component support

On Thu, Nov 19, 2020 at 3:37 PM Chang S. Bae <> wrote:
> literally align with new boot-parameters.
> "xstate.disable=0x60000" will disable AMX on a system that has AMX compiled
> "xstate.enable=0x60000" will enable AMX on a system that does NOT have AMX
> compiled into XFEATURE_MASK_USER_ENABLED (assuming the kernel is new enough
> to support this feature).

What's the purpose of xstate.enable?  I can't really imagine it's
useful for AMX.  I suppose it could be useful for hypothetical
post-AMX features, but that sounds extremely dangerous.  Intel has
changed its strategy so many times on XSTATE extensibility that I find
it quite hard to believe that supporting unknown states is wise.

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