linux-kernel - Re: [PATCH v2 08/20] x86, ACPI: Find acpi tables in initrd early from head

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Date:	Thu, 04 Apr 2013 13:25:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Pekka Enberg <penberg@...nel.org>
CC:	Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, Thomas Renninger <trenn@...e.de>,
	Tang Chen <tangchen@...fujitsu.com>,
	linux-kernel@...r.kernel.org, Jacob Shin <jacob.shin@....com>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 08/20] x86, ACPI: Find acpi tables in initrd early
 from head_32.S/head64.c

On 03/10/2013 03:25 AM, Pekka Enberg wrote:
> 
> What is preventing us from making the 64-bit variant also work in flat
> mode to make the code consistent and not hiding the differences under
> the rug? What am I missing here?
> 

There is no such thing as "flat mode" in 64-bit mode.  We use a #PF
handler to emulate it, but we add the normal kernel offset when doing so.

In the 32-bit case the problem is that the kernel offset is not
available while in linear mode.  It *could* be created using segment
bases, but that would break Xen, I'm pretty sure, and possibly some
other too-clever environments.

	-hpa


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