On 14/10/2022 15:05, Guilherme G. Piccoli wrote: > Commit b041b525dab9 ("x86/split_lock: Make life miserable for split lockers") > changed the way the split lock detector works when in "warn" mode; > basically, not only it shows the warn message, but also intentionally > introduces a slowdown (through sleeping plus serialization mechanism) > on such task. Based on discussions in [0], seems the warning alone > wasn't enough motivation for userspace developers to fix their > applications. > > Happens that originally the proposal in [0] was to add a new mode > which would warns + slowdown the "split locking" task, keeping the > old warn mode untouched. In the end, that idea was discarded and > the regular/default "warn" mode now slowdowns the applications. This > is quite aggressive with regards proprietary/legacy programs that > basically are unable to properly run in kernel with this change. > While is understandable that a malicious application could try a DoS > by split locking, it seems unacceptable to regress old/proprietary > userspace programs through a default configuration that previously > worked. An example of such breakage was reported in [1]. > > So let's add a sysctl to allow controlling the "misery mode" behavior, > as per Thomas suggestion on [2]. This way, users running legacy and/or > proprietary software are allowed to still execute them with a decent > performance while still observe the warning messages on kernel log. > > [0] https://lore.kernel.org/lkml/20220217012721.9694-1-tony.luck@xxxxxxxxx/ > > [1] https://github.com/doitsujin/dxvk/issues/2938 > > [2] https://lore.kernel.org/lkml/87pmf4bter.ffs@tglx/ > > Fixes: b041b525dab9 ("x86/split_lock: Make life miserable for split lockers") > Cc: Andre Almeida <andrealmeid@xxxxxxxxxx> > Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx> > Cc: Joshua Ashton <joshua@xxxxxxxxx> > Cc: Melissa Wen <mwen@xxxxxxxxxx> > Cc: Paul Gofman <pgofman@xxxxxxxxxxxxxxx> > Cc: Pavel Machek <pavel@xxxxxxx> > Cc: Pierre-Loup Griffais <pgriffais@xxxxxxxxxxxxxxxxx> > Cc: Tony Luck <tony.luck@xxxxxxxxx> > Cc: Zebediah Figura <zfigura@xxxxxxxxxxxxxxx> > Suggested-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Signed-off-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> > --- Hi Dave / Thomas, do you think this version is good enough? If so, would be possible to pick it still in the v6.1-rc cycle, since it is a fix? What about the documentation improvements from Bagas, should I re-send (V3) with that, or would you pick them when merging? Thanks in advance, Guilherme