linux-kernel - Re: [PATCH] efi: Clarify Kconfig help for EFI

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Message-ID: <53482E61.8050606@zytor.com>
Date:	Fri, 11 Apr 2014 11:03:13 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Thomas Bächler <thomas@...hlinux.org>,
	Matt Fleming <matt.fleming@...el.com>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] efi: Clarify Kconfig help for EFI_MIXED

On 04/11/2014 10:59 AM, Thomas Bächler wrote:
> EFI stub support is only missing for a 64 bit kernel on 32-bit firmware,
> on 64-bit kernels, EFI stub works as usual.
> ---
> 
> Matt, I don't know if this help was intentionally discouraging,
> however, out of curiosity, I tested this with ovmf, and the
> kernel boots fine on 64-bit firmware bit with EFI stub, and on
> 32-bit firmware using efilinux.
> 
> Documenting this properly is important for distribution kernels.
> We would want to support this on Arch, but not if it means
> introducing a regression for EFI stub users.
> 
>  arch/x86/Kconfig | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index 5b8ec0f..2bbbbb9 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1529,8 +1529,8 @@ config EFI_MIXED
>  	   mode.
>  
>  	   Note that it is not possible to boot a mixed-mode enabled
> -	   kernel via the EFI boot stub - a bootloader that supports
> -	   the EFI handover protocol must be used.
> +	   kernel via the EFI boot stub on 32-bit firmware - a bootloader
> +	   that supports the EFI handover protocol must be used.
>  
>  	   If unsure, say N.
>  

Right, it is really that it is not possible to boot a mixed-mode kernel
on its non-native firmware using the stub, since the stub itself can
only be one way or the other.

	-hpa


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