linux-kernel - efivarfs fails with `No such device` when EFI runtime is missing

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Date:   Tue, 11 May 2021 22:55:03 +0200
From:   Paul Menzel <pmenzel@...gen.mpg.de>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     linux-efi@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: efivarfs fails with `No such device` when EFI runtime is missing

Dear Linux folks,

I migrated a 32-bit GNU/Linux installation from BIOS to EFI. Trying to 
edit the entries in UEFI’s Boot Manager with `efibootmgr`, I got the error:

     EFI variables are not supported on this system

`sudo modprobe efivarfs` fails with

     No such device

After several tries, I found

     [    0.000000] efi: No EFI runtime due to 32/64-bit mismatch with 
kernel

logged by Linux, and then I found the Stack Overflow thread *How could 
32bit kernel read efivars from 64bit UEFI?* [1].

I would have thought, setting EFI variables is just directly writing to 
some storage. But probably not.

Could the error message for the efivarfs load failure be improved, that 
*device* means the runtime service (if I am not mistaken)?

Kind regards,

Paul

[1]: 
https://stackoverflow.com/questions/46610442/how-could-32bit-kernel-read-efivars-from-64bit-uefi