Re: [5.17 regression] "x86/PCI: Ignore E820 reservations for bridge windows on newer systems" breaks suspend/resume

[Thorsten Leemhuis]

[TLDR: I'm adding the regression report below to regzbot, the Linux
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CCing the regression mailing list, as it should be in the loop for all
regressions, as explained here:
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To be sure this issue doesn't fall through the cracks unnoticed, I'm
adding it to regzbot, my Linux kernel regression tracking bot:

#regzbot ^introduced 7f7b4236f204
#regzbot title x86/PCI: "x86/PCI: Ignore E820 reservations for bridge
windows on newer systems" breaks suspend/resume
#regzbot ignore-activity

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Ciao, Thorsten (wearing his 'the Linux kernel's regression tracker' hat)

P.S.: As the Linux kernel's regression tracker I'm getting a lot of
reports on my table. I can only look briefly into most of them and lack
knowledge about most of the areas they concern. I thus unfortunately
will sometimes get things wrong or miss something important. I hope
that's not the case here; if you think it is, don't hesitate to tell me
in a public reply, it's in everyone's interest to set the public record
straight.

On 08.02.22 16:25, Hans de Goede wrote:
> Hi All,
> 
> Unfortunately I've just learned that commit 7f7b4236f204 ("x86/PCI:
> Ignore E820 reservations for bridge windows on newer systems"):
> 
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7f7b4236f2040d19df1ddaf30047128b41e78de7
> 
> breaks suspend/resume on at least one laptop model, the Lenovo ThinkPad
> X1 gen 2, see:
> https://bugzilla.redhat.com/show_bug.cgi?id=2029207
> 
> This regression was actually caught be Fedora already carrying this
> patch for a while now and as such it has been reproduced with 5.15
> with an older version of the patch which still allowed turning the
> new behavior of by adding "pci=use_e820". Dmesg output with and
> without the option has just been attached to the bug, I've not
> analyzed this any further yet.
> 
> I guess that for now this means that we need to revert commit
> 7f7b4236f204. Rafael, I'll send you a revert with a commit msg
> explaining why this needs to be reverted tomorrow.
> 
> More interesting IMHO is finding out another solution. Both the touchpad
> problem which got me looking into this:
> https://bugzilla.redhat.com/show_bug.cgi?id=1868899
> 
> As well as the thunderbolt hotplug issue Mika was looking at:
> https://bugzilla.kernel.org/show_bug.cgi?id=206459
> 
> both are cases where we fail to find a memory-window for a
> BAR which has not been setup yet.
> 
> So I see a couple of options here:
> 
> 1. Detect that the e820 reservations fully cover (one of)
> the PCI bridge main 32 bit memory windows and if that happens
> ignore them. This actually was my first plan when I started
> working on this. In the end I choose the other option
> because Bjorn indicated that in hindsight honoring the e820
> reservations might have been a mistake and maybe we should
> get rid of honoring them all together.
> 
> 2. Have a flag which, when we fail to alloc a 32 bit
> (or 64 bit) memory PCI BAR, is set if not already set
> and then retry the alloc. And make the e820 reservation
> carve-out get skipped in this case.
> 
> 3. When booting with pci=nocrs as a workaround for
> the touchpad case a 64 but memory window ends up getting
> used. There already is some special handling for some
> AMD bridges where if there are no 64 bit memory Windows
> in the _CRS for the bridge, one gets added. Maybe we need
> to do the same for Intel bridges ?
> 
> Please let me know which of these options you think I should
> try to implement next; of course alternative ideas for fixing
> this are also welcome.
> 
> Regards,
> 
> Hans
> 

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