Re: [PATCH 0/2] efi: Expose the runtime-services workqueue via sysfs

[Sebastian Andrzej Siewior]

On 2026-02-09 18:10:52 [+0100], Ard Biesheuvel wrote:
> Hello Sebastian,
> 
> On Thu, 5 Feb 2026, at 12:55, Sebastian Andrzej Siewior wrote:
> > EFI runtime services are disabled on PREEMPT_RT by default which can be
> > overwritten on the boot command line. For native EFI, an invocation
> > requires to disable preemption while a call is made into EFI.
> 
> This is no longer true on arm64 since
> 
> commit a5baf582f4c026c25a206ac121bceade926aec74
> Author: Ard Biesheuvel <ardb@xxxxxxxxxx>
> Date:   Wed Oct 15 22:56:42 2025 +0200
> 
>     arm64/efi: Call EFI runtime services without disabling preemption
> 
> except for some corner cases (reboot, pstore crash dump).

Hmm. While this sounds familiar (and I think you told me that FPU usage
no longer disables preemption here, too) there is x86 for instance. Here
arch_efi_call_virt_setup() disables preemption twice (efi_fpu_begin() +
(firmware_restrict_branch_speculation_start()) followed by
efi_call_virt_save_flags() where interrupts are off. 

Also I don't know if the EFI implementation itself is allowed to disable
interrupts.

> > There are two EFI invocations which are not covered by this
> > - mixed EFI
> >   Used on x86 with 64bit kernel but 32bit EFI. Would it work to use here
> >   the same workqueue mechanism?
> >
> 
> That stuff is beyond obsolete, so I don't think it is relevant for RT.

agreed.

> Acked-by: Ard Biesheuvel <ardb@xxxxxxxxxx>

Oh. Thank you.

Sebastian