linux-kernel - Re: [PATCH] Make it possible to disable efivar

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Date:   Wed, 17 Jun 2020 11:01:54 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Peter Jones <pjones@...hat.com>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Make it possible to disable efivar_ssdt entirely

On Tue, 16 Jun 2020 at 00:47, Ard Biesheuvel <ardb@...nel.org> wrote:
>
> On Mon, 15 Jun 2020 at 22:24, Peter Jones <pjones@...hat.com> wrote:
> >
> > In most cases, such as CONFIG_ACPI_CUSTOM_DSDT and
> > CONFIG_ACPI_TABLE_UPGRADE, boot-time modifications to firmware tables
> > are tied to specific Kconfig options.  Currently this is not the case
> > for modifying the ACPI SSDT via the efivar_ssdt kernel command line
> > option and associated EFI variable.
> >
> > This patch adds CONFIG_EFI_CUSTOM_SSDT_OVERLAYS, which defaults
> > disabled, in order to allow enabling or disabling that feature during
> > the build.
> >
> > Signed-off-by: Peter Jones <pjones@...hat.com>
>
> Thanks Peter.
>
> > ---
> >  drivers/firmware/efi/efi.c   |  2 +-
> >  drivers/firmware/efi/Kconfig | 11 +++++++++++
> >  2 files changed, 12 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> > index 48d0188936c..4b12a598ccf 100644
> > --- a/drivers/firmware/efi/efi.c
> > +++ b/drivers/firmware/efi/efi.c
> > @@ -192,7 +192,7 @@ static void generic_ops_unregister(void)
> >         efivars_unregister(&generic_efivars);
> >  }
> >
> > -#if IS_ENABLED(CONFIG_ACPI)
> > +#if IS_ENABLED(CONFIG_EFI_CUSTOM_SSDT_OVERLAYS)
> >  #define EFIVAR_SSDT_NAME_MAX   16
> >  static char efivar_ssdt[EFIVAR_SSDT_NAME_MAX] __initdata;
> >  static int __init efivar_ssdt_setup(char *str)
> > diff --git a/drivers/firmware/efi/Kconfig b/drivers/firmware/efi/Kconfig
> > index 6b38f9e5d20..fe433f76b03 100644
> > --- a/drivers/firmware/efi/Kconfig
> > +++ b/drivers/firmware/efi/Kconfig
> > @@ -278,3 +278,14 @@ config EFI_EARLYCON
> >         depends on SERIAL_EARLYCON && !ARM && !IA64
> >         select FONT_SUPPORT
> >         select ARCH_USE_MEMREMAP_PROT
> > +
> > +config EFI_CUSTOM_SSDT_OVERLAYS
> > +       bool "Load custom ACPI SSDT overlay from an EFI variable"
> > +       depends on EFI_VARS
>
> Shouldn't this depend on ACPI too?
>

I'll pick this up as a fix (with the ACPI dependency added)

> > +       default ACPI_TABLE_UPGRADE
> > +       help
> > +         Allow loading of an ACPI SSDT overlay from an EFI variable specified
> > +         by a kernel command line option.
> > +
> > +         See Documentation/admin-guide/acpi/ssdt-overlays.rst for more
> > +         information.
> > --
> > 2.26.2
> >