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Message-ID: <ecbc58bc-a250-cf39-dea6-9b0b1c3e6503@intel.com>
Date:   Thu, 29 Sep 2022 09:26:38 -0700
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Subject: Re: [PATCH] x86/split_lock: Restore warn mode (and add a new one) to
 avoid userspace regression
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To:     "Guilherme G. Piccoli" <gpiccoli@igalia.com>, tony.luck@intel.com,
        tglx@linutronix.de, linux-kernel@vger.kernel.org, x86@kernel.org
Cc:     mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, luto@kernel.org, kernel-dev@igalia.com,
        kernel@gpiccoli.net, Fenghua Yu <fenghua.yu@intel.com>,
        Joshua Ashton <joshua@froggi.es>,
        Paul Gofman <pgofman@codeweavers.com>,
        Pavel Machek <pavel@denx.de>,
        Pierre-Loup Griffais <pgriffais@valvesoftware.com>,
        Melissa Wen <mwen@igalia.com>
References: <20220928142109.150263-1-gpiccoli@igalia.com>
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From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <7917fde2-a381-5404-c5ae-6ffd433f85ec@igalia.com>
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On 9/29/22 08:30, Guilherme G. Piccoli wrote:
>> 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.

Let's be precise here, though.  It isn't that folks can't play.  It's
that we *intentionally* put something in place that kept them from
playing.  They can play just fine after disabling split lock detection.

> 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?
They don't have to live with it.  They can turn it off.  That's why the
command-line disable is there.

The real question in my head is whether the misery is intentional or
not.  Is breaking games what folks _intended_ with
split_lock_detect=warn?  Or, is this a more severe penalty than we
expected and maybe we should back off for the default?