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: <7917fde2-a381-5404-c5ae-6ffd433f85ec@igalia.com>
Date:   Thu, 29 Sep 2022 12:30:09 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Dave Hansen <dave.hansen@...el.com>, tony.luck@...el.com,
        tglx@...utronix.de, linux-kernel@...r.kernel.org, x86@...nel.org
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, luto@...nel.org, kernel-dev@...lia.com,
        kernel@...ccoli.net, Fenghua Yu <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 29/09/2022 12:17, Dave Hansen wrote:
> [...]
>> Hi Dave, thanks for your response. I really appreciated your reasoning,
>> and I think it's a good argument. In the end, adding misery would harm
>> the users that are unlikely to be able to fix (or at least, fix quickly)
>> the split lock situation, like games or legacy/proprietary code.
>>
>> I have a revert removing the misery ready and tested, let me know if I
>> should submit it.
> 
> I'm a bit of a late arrival to the split lock party, so I'm a bit
> hesitant to merge any changes immediately.
> 

OK, agree that we could indeed gather more opinions, like Thomas' and
other interested parties. But...


> How about we give it a few weeks and see if the current behavior impacts
> anyone else?  Maybe the best route will be more clear then.

...I disagree in just letting it fly for weeks with all players of God
of War 2 running modern Intel chips unable to play in 5.19+ because of
this change.

Certainly we have more games/applications that are impacted, I just
don't think we should wait on having 3 userspace breakages reported, for
example, to take an action - why should gamers live with this for an
arbitrary amount of time, until others report more issues?

Cheers,


Guilherme