linux-kernel - Re: [PATCH] x86 boot: Pass E820 memory map entries more than 128 via linked list of setup data

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Date:	Tue, 24 Jun 2008 09:09:34 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Paul Jackson <pj@....com>
Cc:	mingo@...e.hu, hpa@...or.com, andi@...stfloor.org,
	mingo@...hat.com, tglx@...utronix.de, linux-kernel@...r.kernel.org,
	yhlu.kernel@...il.com
Subject: Re: [PATCH] x86 boot: Pass E820 memory map entries more than 128
	via linked list of setup data

On Mon, 2008-06-23 at 04:48 -0500, Paul Jackson wrote:
> Huang wrote:
> > 4. Current EFI memmap based code does not work properly in all
> > situation, for example it can not works with kernel parameter:
> > "memmap=exactmap, memmap=<xxx>, ...", "mem=<xxx>" or "noefi".
> 
> With "noefi" parameter, my EFI memmap based code is not supposed
> to do anything.  The "noefi" parameter asks the kernel to ignore
> any EFI support in the firmware it is booting from.

"noefi" is used to specify that the EFI runtime services should be
disabled in kernel. But the memmap should be complete.

> Could you tell me more what you mean by "does not work properly?"

OK. It is OK for your code with "noefi". The remaining issues:

If "memmap=exactmap memmap=<xxx>" is specified in kernel command line.
The user defined memmap should override that from firmware. But your
code is executed after the user defined memmap is parsed, so the memmap
from firmware will override that from user. This does not conform the
semantics of "memmap=exactmap ...". Same issue for "mem=<xxx>".

Another issue is that the size of E820 memmap required on EFI system
must be two times bigger than that really needed. Because at first the
E820 memmap is filled with the entries from E820 and E820_EXT, then that
from EFI memmap is appended.

Best Regards,
Huang Ying

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