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

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Message-ID: <Z8_mDOpoB5FloreP@gmail.com>
Date: Tue, 11 Mar 2025 08:28:12 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Balbir Singh <balbirs@...dia.com>
Cc: Bert Karwatzki <spasswolf@....de>, 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


* Balbir Singh <balbirs@...dia.com> wrote:

> 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

[ Just a side note: disabling CONFIG_PCI_P2PDMA will have the same 
  effect *on KASRL* memory layout as reverting 7ffb791423c, but 
  disabling support for the P2P DMA PCI feature may have other side 
  effects. ]

Thanks,

	Ingo