linux-kernel - Re: [PATCH] x86/split_lock: Restore warn mode (and add a new one) to avoid userspace regression

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Message-ID: <20221006090418.GA14960@amd>
Date:   Thu, 6 Oct 2022 11:04:18 +0200
From:   Pavel Machek <pavel@...x.de>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "kernel-dev@...lia.com" <kernel-dev@...lia.com>,
        "kernel@...ccoli.net" <kernel@...ccoli.net>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        Joshua Ashton <joshua@...ggi.es>,
        Paul Gofman <pgofman@...eweavers.com>,
        Pavel Machek <pavel@...x.de>,
        Pierre-Loup Griffais <pgriffais@...vesoftware.com>,
        Melissa Wen <mwen@...lia.com>
Subject: Re: [PATCH] x86/split_lock: Restore warn mode (and add a new one) to
 avoid userspace regression

On Wed 2022-09-28 20:24:23, Luck, Tony wrote:
> > So let's revamp the idea of having another option/mode for the split
> > lock detector, which is hereby called "seq" (based on the original
> > "sequential" naming in [0]). Also introduces a Kconfig option to give
> > the option of Linux vendors have a choice what mode should be their
> > default. While at it, fix/improve the documentation about bus locking.
> >
> > [1] https://github.com/doitsujin/dxvk/issues/2938
> 
> Why not just use the workaround suggested in that bug report:
> 
>    "so manual switching from default setting to split_lock_detect=off helps as workaround here"
> 
> If you add this extra mode, I'm going to argue that the kernel default
> should be "seq" rather than "warn". So these game players will need
> to add a split_lock_detect=off (or warn) option.

Kernel should not cause userland regressions, and this is one. That
should make it pretty clear what the solution is.

And no, I don't like CONFIG option, either.

Best regards,
								Pavel
-- 
DENX Software Engineering GmbH,      Managing Director: Wolfgang Denk
HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany

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