Re: [PATCH] efi: don't iterate over EFI vars pointlessly if no SSDT override was specified

[Scott Talbert <swt@techie.net>]

On Thu, 12 Sep 2019, Ard Biesheuvel wrote:

> The kernel command line option efivar_ssdt= allows a EFI variable name
> to be specified which contains an ACPI SSDT table that will be loaded
> into memory by the OS.
>
> Currently, that code will always iterate over the EFI variables and
> compare each name with the provided name, even if the command line
> option wasn't set to begin with.
>
> So bail early when no variable name was provided.
>
> Cc: Scott Talbert <swt@techie.net>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> drivers/firmware/efi/efi.c | 3 +++
> 1 file changed, 3 insertions(+)
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index ad3b1f4866b3..8f020827cdd3 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -282,6 +282,9 @@ static __init int efivar_ssdt_load(void)
> 	void *data;
> 	int ret;
>
> +	if (!efivar_ssdt[0])
> +		return 0;
> +
> 	ret = efivar_init(efivar_ssdt_iter, &entries, true, &entries);
>
> 	list_for_each_entry_safe(entry, aux, &entries, list) {

Thanks for the quick fix!

I can confirm this fixes booting on my Mac Pro 2012 system when applied to 
5.3-rc7.

Whenever this makes it in, if it could be targeted for the stable kernels 
as well, that would be appreciated.

Thanks,
Scott