Bug: kexec on Lenovo ThinkPad T480 disables EFI mode

[Baoquan He]

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On 10/28/22 at 01:02pm, ns at tfwno.gf wrote:
> Greetings,
> 
> I've been hitting a bug on my Lenovo ThinkPad T480 where kexecing will
> cause EFI mode (if that's the right term for it) to be unconditionally
> disabled, even when not using the --noefi option to kexec.
> 
> What I mean by "EFI mode" being disabled, more than just EFI runtime
> services, is that basically nothing about the system's EFI is visible
> post-kexec. Normally you have a message like this in dmesg when the
> system is booted in EFI mode:
> 
> [    0.000000] efi: EFI v2.70 by EDK II
> [    0.000000] efi: SMBIOS=0x7f98a000 ACPI=0x7fb7e000 ACPI 2.0=0x7fb7e014
> MEMATTR=0x7ec63018
> (obviously not the real firmware of the machine I'm talking about, but I
> can also send that if it would be of any help)
> 
> No such message pops up in my dmesg as a result of this bug, & this
> causes some fallout like being unable to find the system's DMI
> information:
> 
> <6>[    0.000000] DMI not present or invalid.
> 
> The efivarfs module also fails to load with -ENODEV.
> 
> I've tried also booting with efi=runtime explicitly but it doesn't
> change anything. The kernel still does not print the name of the EFI
> firmware, DMI is still missing, & efivarfs still fails to load.
> 
> I've been using the kexec_load syscall for all these tests, if it's
> important.
> 
> Also, to make it very clear, all this only ever happens post-kexec. When
> booting straight from UEFI (with the EFI stub), all the aforementioned
> stuff that fails works perfectly fine (i.e. name of firmware is printed,
> DMI is properly found, & efivarfs loads & mounts just fine).
> 
> This is reproducible with a vanilla 6.1-rc2 kernel. I've been trying to
> bisect it, but it seems like it goes pretty far back. I've got vanilla
> mainline kernel builds dating back to 5.17 that have the exact same
> issue. It might be worth noting that during this testing, I made sure
> the version of the kernel being kexeced & the kernel kexecing were the
> same version. It may not have been a problem in older kernels, but that
> would be difficult to test for me (a pretty important driver for this
> machine was only merged during v5.17-rc4). So it may not have been a
> regression & just a hidden problem since time immemorial.
> 
> I am willing to test any patches I may get to further debug or fix
> this issue, preferably based on the current state of torvalds/linux.git.
> I can build & test kernels quite a few times per day.
> 
> I can also send any important materials (kernel config, dmesg, firmware
> information, so on & so forth) on request. I'll also just mention I'm
> using kexec-tools 2.0.24 upfront, if it matters.
> 
> Regards,
> 
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