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

[Yeoreum Yun <yeoreum.yun@arm.com>]

> 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@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.
> 
> 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().

-- 
Sincerely,
Yeoreum Yun