Re: [RFC PATCH] efivarfs: Introduce efivarfs refresh remount

[Ard Biesheuvel]

On Wed, 15 Jan 2025 at 15:58, James Bottomley
<James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
>
> On Wed, 2025-01-15 at 22:49 +0800, Weizhao Ouyang wrote:
> > On Wed, Jan 15, 2025 at 10:34 PM James Bottomley
> > <James.Bottomley@xxxxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > On Wed, 2025-01-15 at 22:14 +0800, Weizhao Ouyang wrote:
> > > > Currently, when setting efi variables through the runtime
> > > > service, efivarfs cannot sync variable updates properly.
> > > > Introduce efivarfs refresh remount to support efivarfs
> > > > information updates from other sources.
> > >
> > > What other sources could there possibly be?  While the Linux kernel
> > > has sole possession of the EFI RT interface after ExitBootServices
> > > has been called, nothing else should be able to update the
> > > variables except efivarfs.  This is a guarantee from UEFI so why do
> > > you think we can't rely on it?
> >
> > One route that may exist is: drivers/firmware/efi/test/efi_test.c
> > holds some ioctls to call runtime service.
>
> That's not supposed to be used for anything other than direct testing
> using the firmware test suite, which shouldn't impact production use of
> efivarfs because it's defined to be N in Kconfig.   However, if we
> suddenly decided there was a use case for production systems running
> the test suite, the way forwards would be a notifier that tells
> efivarfs about successful updates to variables as they occur without
> having to remount.
>

I'd argue that running efi_test while efivarfs is mounted renders your
test results useless, and so there is no need to make them play nicely
together.