linux-kernel - Re: [PATCH] x86/fpu: Correct pkru/xstate inconsistency

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Date:   Tue, 15 Feb 2022 09:10:01 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Brian Geffon <bgeffon@...gle.com>,
        Guenter Roeck <groeck@...gle.com>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Willis Kung <williskung@...gle.com>,
        Borislav Petkov <bp@...e.de>,
        Andy Lutomirski <luto@...nel.org>,
        "# v4 . 10+" <stable@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] x86/fpu: Correct pkru/xstate inconsistency

On 2/15/22 08:19, Brian Geffon wrote:
> This only applies before 5.13, so 5.10.y and 5.4.y, the behavior
> decoupled PKRU from xstate in a long series from Thomas Gleixner, but
> the first commit where this would have been fixed in 5.13 would be:
> 
>   commit 954436989cc550dd91aab98363240c9c0a4b7e23
>   Author: Thomas Gleixner <tglx@...utronix.de>
>   Date:   Wed Jun 23 14:02:21 2021 +0200
> 
>     x86/fpu: Remove PKRU handling from switch_fpu_finish()

Could you also describe why the >=5.13 fix for this isn't suitable for
older kernels?