linux-kernel - Re: [PATCH 4/8] x86 boot: allow overlapping ebda and efi memmap memory ranges

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Message-Id: <1213606435.12968.14.camel@caritas-dev.intel.com>
Date:	Mon, 16 Jun 2008 16:53:55 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Paul Jackson <pj@....com>
Cc:	mingo@...e.hu, tglx@...utronix.de, yhlu.kernel@...il.com,
	steiner@....com, travis@....com, hpa@...or.com,
	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 4/8] x86 boot: allow overlapping ebda and efi memmap
	memory ranges

On Mon, 2008-06-16 at 03:24 -0500, Paul Jackson wrote:
> Huang wrote:
> >  I think it is better to change boot loader to avoid memory area of EBDA.
> 
> Would this require the bootloader to know the kernels rather arbitrary
> heuristics for inventing and placing an EBDA area, in reserve_ebda_region()?

I think it is sufficient for boot loader to avoid memory area from
0x9f000 to 0x100000. This can be seen as compatible code for legacy
BIOS.

> In general, I would think it better not to have to code into the EFI
> firmware or bootloader such knowledge.  But perhaps I am wrong here.
> 
> If the kernel is going to reserve an EBDA region even if no EBDA is
> requested by the BIOS, then I would think that the kernel should be
> more tolerant of BIOS's that put something else in that place.
> 
> > Or do not reserve EBDA on EFI system.
> 
> I suppose.  This would have been a bigger change than I could
> suggest.  For all I know, there are existing systems using EBDA
> and EFI together.  Would this change break them?
> 
> If you have good reason to know that's essentially impossible then
> I have no objections, so far as my needs go, to not reserving EBDA
> on EFI systems.

I think if EBDA area is used in EFI system, it should be reserved in EFI
memory map.

Best Regards,
Huang Ying

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