Re: [PATCH] firmware: efi: add a separate timeout for UpdateCapsule()

["Ard Biesheuvel" <ardb@kernel.org>]

On Thu, 3 Sep 2026, at 16:10, Yeoreum Yun wrote:
> Hi Ard,
>
>> Hello Yeoreum Yun,
>> 
>> On Thu, 3 Sep 2026, at 13:32, Yeoreum Yun wrote:
>> > On platforms that allows to update firmware in runtime, UpdateCapsule()
>> > may immediately write a firmware image to persistent storage.
>> > This operation can take longer than EFI_RTS_TIMEOUT.
>> >
>> > Use a separate timeout for the UpdateCapsule() runtime service. By
>> > default, wait indefinitely to avoid interrupting an ongoing firmware
>> > update. Administrators may configure an appropriate timeout, in seconds,
>> > through /sys/firmware/efi/capsule_update_timeout.
>> >
>> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
>> > ---
>> >  drivers/firmware/efi/efi.c              | 41 +++++++++++++++++++++++++
>> >  drivers/firmware/efi/runtime-wrappers.c | 14 +++------
>> >  include/linux/efi.h                     | 10 ++++++
>> >  3 files changed, 55 insertions(+), 10 deletions(-)
>> >
>> 
>> Given that UpdateCapsule() is rarely used these days at runtime, I
>> wonder if we should just call it synchronously instead of via the
>> EFI workqueue.
>> 
>> I assume that would also solve the timeout issue?
>
> Might be. But it would make *non-preemptible* for UpdateCapsule().
> AFAIK the purpose of running runtime service with efi_queue to
> run it in indepdent context and to be preemtible in case of arm64.
>

No.

> Since most of UpdateCapsule() will be called via capsule-loader's misc
> device, if UpdateCaspule() is called synchronously, It would be
> non-preemtible in arm64 platform.
>
> But, some platform could be preemptible while updating firmware so
> I think it would be better that it would be called via EFI workqueue.
>

EFI runtime service invocations are preemptible on arm64, so this is
not a problem.