linux-kernel - Re: [RFC PATCH v2] x86/arch_prctl: Add ARCH_SET

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Date:   Tue, 7 Apr 2020 14:21:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Keno Fischer <keno@...iacomputing.com>
Cc:     linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andi Kleen <andi@...stfloor.org>,
        Kyle Huey <khuey@...ehuey.com>,
        Robert O'Callahan <robert@...llahan.org>
Subject: Re: [RFC PATCH v2] x86/arch_prctl: Add ARCH_SET_XCR0 to set XCR0
 per-thread

On Mon, Apr 06, 2020 at 09:12:59PM -0400, Keno Fischer wrote:
> This is a follow-up to my from two-years ago [1]. I've been using
> rebased versions of that patch locally for my needs, but I've had
> more people ask me about this patch recently, so I figured, I'd
> have another go at this. Even if this doesn't make it into mainline,
> I figure I can at least improve the quality of the patch for others
> who want to use it. That's said, here's how this version is
> different from v1:

Aside of having an inconsistent comment style and whitespace damage, it
adds exports without a module user.

But my main reason for replying is asking: 'What the heck for?'

You had a fairly long changelog detailing what the patchd does; but I've
failed to find a single word on _WHY_ we want to do any of that.