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@xxxxxxxxxx> wrote:
Add Dave to CC
On 10/28/22 at 01:02pm, ns@xxxxxxxx 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,
>
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