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

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Message-ID: <CAMj1kXGLwyk9ibSDXBfeu06HV4x4VtbWbKv20KNzkXpbTxBSXg@mail.gmail.com>
Date:   Tue, 16 Jun 2020 00:47:14 +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 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?

> +       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
>