linux-kernel - Re: [PATCH] efi/efivars: create efivars mount point when get variable services are available

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Date:   Thu, 20 Aug 2020 11:30:27 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     "Lee, Chun-Yi" <joeyli.kernel@...il.com>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Lee, Chun-Yi" <jlee@...e.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>
Subject: Re: [PATCH] efi/efivars: create efivars mount point when get variable
 services are available

On Wed, 19 Aug 2020 at 11:28, Lee, Chun-Yi <joeyli.kernel@...il.com> wrote:
>
> The efivars filesystem depends on GetVariable or GetNextVariable EFI
> runtime services. So the /sys/firmware/efi/efivars does not need to be
> created when GetVariable and GetNextVariable are not available.
>
> It is useful for userland to determine the availability of efivars
> filesystem.
>
> Cc: Ilias Apalodimas <ilias.apalodimas@...aro.org>
> Cc: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: "Lee, Chun-Yi" <jlee@...e.com>

Hello Joey,

This is not the right check to perform here: the efivarfs code could
be instantiated using a different efivars abstraction, so whether the
RT services are implemented is not entirely relevant.

Please look at commit f88814cc2578c121e6edef686365036db72af0ed
("efi/efivars: Expose RT service availability via efivars
abstraction") for an explanation of the underlying issue, and update
your patch accordingly.


> ---
>  drivers/firmware/efi/efi.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index fdd1db025dbf..929fbf4dfd5d 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -404,11 +404,14 @@ static int __init efisubsys_init(void)
>         if (error)
>                 goto err_remove_group;
>
> -       /* and the standard mountpoint for efivarfs */
> -       error = sysfs_create_mount_point(efi_kobj, "efivars");
> -       if (error) {
> -               pr_err("efivars: Subsystem registration failed.\n");
> -               goto err_remove_group;
> +       if (efi_rt_services_supported(EFI_RT_SUPPORTED_GET_VARIABLE |
> +                                     EFI_RT_SUPPORTED_GET_NEXT_VARIABLE_NAME)) {
> +               /* and the standard mountpoint for efivarfs */
> +               error = sysfs_create_mount_point(efi_kobj, "efivars");
> +               if (error) {
> +                       pr_err("efivars: Subsystem registration failed.\n");
> +                       goto err_remove_group;
> +               }
>         }
>
>         if (efi_enabled(EFI_DBG) && efi_enabled(EFI_PRESERVE_BS_REGIONS))
> --
> 2.16.4
>