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

[Dave Hansen <dave.hansen@intel.com>]

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?