linux-kernel - Re: [patch 7/7 v2] x86: add xloadflags bit for efi runtime support on kexec

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Date:	Wed, 13 Nov 2013 08:20:45 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	dyoung@...hat.com, linux-kernel@...r.kernel.org
CC:	linux-efi@...r.kernel.org, x86@...nel.org, mjg59@...f.ucam.org,
	James.Bottomley@...senPartnership.com, vgoyal@...hat.com,
	ebiederm@...ssion.com, horms@...ge.net.au,
	kexec@...ts.infradead.org, bp@...en8.de
Subject: Re: [patch 7/7 v2] x86: add xloadflags bit for efi runtime support
 on kexec

On 11/05/2013 12:20 AM, dyoung@...hat.com wrote:
> Old kexec-tools can not load new kernel. The reason is previously kexec-tools
> do not fill efi_info in x86 setup header thus efi init fail and switch
> to noefi boot. In new kexec-tools it will by default fill efi_info and
> pass other efi required infomation to 2nd kernel so kexec kernel efi
> initialization will success finally.
> 
> To prevent from breaking userspace, add a new xloadflags bit so kexec-tools
> will check the flag and switch to old logic.
> 
> Signed-off-by: Dave Young <dyoung@...hat.com>
> ---
>  arch/x86/boot/header.S                |    9 ++++++++-
>  arch/x86/include/uapi/asm/bootparam.h |    1 +
>  2 files changed, 9 insertions(+), 1 deletion(-)
> 
> --- linux-2.6.orig/arch/x86/boot/header.S
> +++ linux-2.6/arch/x86/boot/header.S
> @@ -391,7 +391,14 @@ xloadflags:
>  #else
>  # define XLF23 0
>  #endif
> -			.word XLF0 | XLF1 | XLF23
> +
> +#if defined(CONFIG_X86_64) && defined(CONFIG_EFI)
> +# define XLF4 XLF_EFI_KEXEC
> +#else
> +# define XLF4 0
> +#endif
> +
> +			.word XLF0 | XLF1 | XLF23 | XLF4
>  
>  cmdline_size:   .long   COMMAND_LINE_SIZE-1     #length of the command line,
>                                                  #added with boot protocol
> --- linux-2.6.orig/arch/x86/include/uapi/asm/bootparam.h
> +++ linux-2.6/arch/x86/include/uapi/asm/bootparam.h
> @@ -24,6 +24,7 @@
>  #define XLF_CAN_BE_LOADED_ABOVE_4G	(1<<1)
>  #define XLF_EFI_HANDOVER_32		(1<<2)
>  #define XLF_EFI_HANDOVER_64		(1<<3)
> +#define XLF_EFI_KEXEC			(1<<4)
>  
>  #ifndef __ASSEMBLY__
>  
> 

Also needs to be added to Documentation/x86/boot.txt with the exact
semantics being exposed.

	-hpa

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