linux-kernel - Re: [PATCH 0/3] x86_64 EFI runtime service support

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Date:	Mon, 20 Aug 2007 13:14:47 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <ak@...e.de>,
	Chandramouli Narayanan <mouli@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] x86_64 EFI runtime service support

On Sun, 2007-08-19 at 16:25 -0600, Eric W. Biederman wrote:
> "Huang, Ying" <ying.huang@...el.com> writes:
> >> > +#define EFI_LOADER_SIG ((unsigned char *)(PARAM+0x1c0))
> >> > +#define EFI_MEMDESC_SIZE (*((unsigned int *) (PARAM+0x1c4)))
> >> > +#define EFI_MEMDESC_VERSION (*((unsigned int *) (PARAM+0x1c8)))
> >> > +#define EFI_MEMMAP_SIZE (*((unsigned int *) (PARAM+0x1cc)))
> >> > +#define EFI_MEMMAP (*((unsigned long *)(PARAM+0x1d0)))
> >> > +#define EFI_SYSTAB (*((unsigned long *)(PARAM+0x1d8)))
> >> >  #define MOUNT_ROOT_RDONLY (*(unsigned short *) (PARAM+0x1F2))
> Be very very very  careful how you talk about this.
> 
> I have seen machines in the wild a 64bit processor and a 32bit EFI.
> So this is not a linux architecture issue, or a cpu architecture
> issue.  This is an EFI architecture issue.
> 
> This is an issue of do you have a 32bit or a 64bit EFI implementation
> on your machine.  Which is very different.
> 
> We should be able to boot a 32bit kernel with a 64bit EFI.
> We should be able to boot a 64bit kernel with a 32bit EFI.
> 
> Maybe our response is to ignore the information from elilo so
> we don't attempt EFI runtime calls but the boot information should
> be unambiguous.
> 
> So we need to be able to look at the data and answer these questions.
> - Is EFI present?
> - Is EFI 32bit?
> - Is EFI 64bit?

Yes, it is necessary to distinguish these situations. I think the
EFI_LOADER_SIG defined above can be used for that. For example the
following signature can be defined:

32-bit EFI	EL32
64-bit EFI	EL64

All other values will be treated as no EFI present.

If struct setup_data proposed by H. Peter Anvin is used for EFI
information passed from bootloader, two "type" can be defined for 32-bit
EFI and 64-bit EFI, such as SETUP_DATA_TYPE_EFI_32 and
SETUP_DATA_TYPE_EFI64. If either type is not presented in "linked list
of struct setup_data", it is considered that EFI is not present.

Best Regards,
Huang Ying
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