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().

Hi Ard,

Could there be any issues with doing it this way, or would there be
a better approach?

-- 
Sincerely,
Yeoreum Yun