linux-kernel - Re: commit 7ffb791423c7 breaks steam game

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Message-ID: <9a5df5627d3d72b2a97f501dfb7d944cc1e9920f.camel@web.de>
Date: Tue, 11 Mar 2025 19:24:29 +0100
From: Bert Karwatzki <spasswolf@....de>
To: Balbir Singh <balbirs@...dia.com>
Cc: Ingo Molnar <mingo@...nel.org>, Kees Cook <kees@...nel.org>, Bjorn
 Helgaas	 <bhelgaas@...gle.com>, Linus Torvalds
 <torvalds@...ux-foundation.org>, Peter Zijlstra <peterz@...radead.org>,
 Andy Lutomirski <luto@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: commit 7ffb791423c7 breaks steam game

Am Dienstag, dem 11.03.2025 um 12:15 +0100 schrieb Bert Karwatzki:
> Am Dienstag, dem 11.03.2025 um 18:19 +1100 schrieb Balbir Singh:
> > On 3/11/25 08:48, Balbir Singh wrote:
> > > On 3/10/25 22:22, Bert Karwatzki wrote:
> > > > Using linux next-20250307 to play the game stellaris via steam I noticed that
> > > > loading the game gets sluggish with the progress bar getting stuck at 100%.
> > > > In this situation mouse and keyboard inputs don't work properly anymore.
> > > > Switching to a VT and killing stellaris somewhat fixes the situation though in
> > > > one instance the touchpad did not work after that. I bisected this between
> > > > v6.14-rc5 and next-20250307 and got this as the first bad commit:
> > > >
> > > > 7ffb791423c7c518269a9aad35039ef824a40adb is the first bad commit
> > > > commit 7ffb791423c7c518269a9aad35039ef824a40adb (HEAD)
> > > > Author: Balbir Singh <balbirs@...dia.com>
> > > > Date:   Fri Feb 7 10:42:34 2025 +1100
> > > >
> > > >     x86/kaslr: Reduce KASLR entropy on most x86 systems
> > > >
> > > > Reverting commit 7ffb791423c7 in next-20250307 fixes the issue for me.
> > > >
> > >
> > > Thanks for the report! Could you also share the dmesg? Do you have any proprietary
> > > modules loaded? Could you also share the output of /proc/iomem (captured as sudo)?
> > > The lspci output is useful, lspci -vvv (captured with sudo) would help see where
> > > the BAR regions are, specifically before and after the patch. Could you also share
> > > the kernel config?
> > >
> > > I assume your config has CONFIG_PCI_P2PDMA enabled. Did the system ever work with
> > > nokaslr for you?
> > >
> > > I am a little surprised that reducing the entropy causes these issues and having
> > > a larger direct map causes these issues.
> >
> > Hi, Bert
> >
> > I tried to reproduce the issue at my end, but could not. I am new to Steam and my
> > hardware/games are also different. From what I could gather, Steam is a 32 bit
> > application that uses SDL. For my testing I used Xorg, not wayland
> >
> > In addition to the above?
> >
> > 1. Could you confirm if the mouse/keyboard work outside of Steam?
> > 2. Does evtest /dev/input/<mouse device> show anything?
> > 3. We could run the kernel with nokaslr and see if the issue reproduces?
> > 4. As a test, we could try disabling CONFIG_PCI_P2PDMA in the kernel config,
> > build boot and test, this has the same effect has not having the patch
> >
> > Balbir
> >
>
> 1. The problem is not with steam but specifically with the game stellaris (which
> can be started without steam). As long as stellaris is running there is a ~2s
> delay in keyboard and mouse input (for everything), killing stellaris restores
> input to normal.
> 2 evtest /dev/input/event{1,3,4} (keyboard, touchpad, mouse) seems to show the
> same output whether stellaris is running or not, only if it's running there's
> the mentioned delay.
> 3. For some weird reason my kernel does not recongnize the nokaslr cmdline
> parameter, so I build a kernel without CONFIG_RANDOMIZE_BASE and this does NOT
> fix the issue.
> 4. Most surprisingly removing CONFIG_PCI_P2PDMA also does NOT fix the issue.
>
> Bert Karwatzki

I've done more experimenting regarding 4.:
next-20250307 with "CONFIG_RANDOMIZE_BASE=y" AND "CONFIG_PCI_P2PDMA is not set"
works as expected (i.e. no input lag when stellaris is running)

next-20250307 with "CONFIG_RANDOMIZE_BASE is not set" AND "CONFIG_PCI_P2PDMA is
not set" also shows the buggy behaviour (i.e. input lag when stellaris is
running) (this was the configuration I tested before)

As a sidenote, I've tested several kernel with nokaslr as command line parameter
(6.1.128, 6.8.12, 6.12.17 (the debian sid distributional kernel)) and nokaslr is
not recognized as a command line parameter in any of them


Bert Karwatzki