linux-kernel - Re: [PATCH v2 14/22] x86/fpu/xstate: Inherit dynamic user state when used in the parent

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Date:   Thu, 19 Nov 2020 21:08:03 -0800
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>,
        "Liu, Jing2" <jing2.liu@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 14/22] x86/fpu/xstate: Inherit dynamic user state when
 used in the parent

On Thu, Nov 19, 2020 at 3:37 PM Chang S. Bae <chang.seok.bae@...el.com> wrote:
>
> When a new task is created, the kernel copies all the states from the
> parent. If the parent already has any dynamic user state in use, the new
> task has to expand the XSAVE buffer to save them. Also, disable the
> associated first-use fault.

This seems like a mistake.  If init uses AMX for some misguided
reason, ever task on the whole system will end up with AMX state
allocated.