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

[Ard Biesheuvel]

On Tue, 15 Sep 2026, at 10:49, Yeoreum Yun wrote:
>> > On Thu, 3 Sep 2026, at 16:29, Ard Biesheuvel wrote:
>> > > 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@xxxxxxx>
>> > >>> > ---
>> > >>> >  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.
>> > 
>> > Ah wait - you're right, they are only preemptible when invoked from the
>> > work queue.
>> 
>> Yes. That's why I think it would be better to call via EFI workqueue
>> when I see arch_efi_call_virt_setup().
>
> Hi Ard,
>
> Could there be any issues with doing it this way, or would there be
> a better approach?
>

Would it make sense to simply have different limits for UpdateCapsule() and
for everything else? How much longer than 2 minutes do you need in the
typical case?