Messages in this thread | | | Date | Sat, 05 Nov 2022 14:16:30 +0000 | From | ns@tfwno ... | Subject | Re: Bug: kexec on Lenovo ThinkPad T480 disables EFI mode |
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On 2022-11-05 05:49, Dave Young wrote: > Baoquan, thanks for cc me. > > On Sat, 5 Nov 2022 at 11:10, Baoquan He <bhe@redhat.com> wrote: >> >> Add Dave to CC >> >> On 10/28/22 at 01:02pm, ns@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. > > Can you check the efi runtime in sysfs: > ls /sys/firmware/efi/runtime-map/ > > If nothing then maybe you did not enable CONFIG_EFI_RUNTIME_MAP=y, it > is needed for kexec UEFI boot on x86_64.
Oh my, it really is that simple.
Indeed, enabling this in the pre-kexec kernel fixes it all up. I had blindly disabled it in my quest to downsize the pre-kexec kernel to reduce boot time (it only runs a bootloader). In hindsight, the firmware drivers section is not really a good section to tweak on a whim.
I'm terribly sorry to have taken your time to "fix" this "bug". But I must ask, is there any reason why this is a visible config option, or at least not gated behind CONFIG_EXPERT? drivers/firmware/efi/runtime-map.c is pretty tiny, & considering it depends on CONFIG_KEXEC_CORE, one probably wants to have kexec work properly if they can even enable it. I admit the help text for it is arguably pretty good, but I feel like the config option is only really useful for embedded, the same enviroments where people would disable stuff like CONFIG_DMI -- a config option that I would argue is pretty justifiably gated behind CONFIG_EXPERT, because far too many systems break without it & it's pretty small code, so really not worth it unless you absolutely know what you're doing. Similarly, I don't really think there's much value in disabling the ability to kexec without the firmware except if you're heavily informed & must have the size reduction, especially since in EFI land that's where your DMI info comes from, if I were to argue for it on the basis of CONFIG_DMI being gated. In summary, it can cause quite a bit of unnecessary confusion despite only being useful to a very small minority of users.
Thank you!
> > Otherwise you can add debug printf in kexec-tools efi error path to > see what is wrong. > kexec/arch/i386/x86-linux-setup.c : function setup_efi_data > > And if it still not work please post your kernel config, I can have a > try although I do not have the t480 now. > > >> > >> > Regards, >> > >> > _______________________________________________ >> > kexec mailing list >> > kexec@lists.infradead.org >> > http://lists.infradead.org/mailman/listinfo/kexec >> > >>
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