linux-kernel - Re: More E820 brokenness

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Message-ID: <20070927223336.GB4755@cosmic.amd.com>
Date:	Thu, 27 Sep 2007 16:33:36 -0600
From:	"Jordan Crouse" <jordan.crouse@....com>
To:	"H. Peter Anvin" <hpa@...or.com>
cc:	jkeating@...hat.com, "Joerg Pommnitz" <pommnitz@...oo.com>,
	"Chuck Ebbert" <cebbert@...hat.com>,
	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	"Andi Kleen" <ak@...e.de>
Subject: Re: More E820 brokenness

On 27/09/07 15:17 -0700, H. Peter Anvin wrote:
> As luck would have it, it's not just an obscure Geode system which has a
> broken E820 implementation.  Today I received a bug report about a Dell
> system (XPS M1330) with broken E820.
> 
> Unfortunately, the workaround for the Geode breaks this system, because
> x86-64 doesn't fall back to the e801/88 information like the i386 kernel
> does.
> 
> I wonder if the relevant people could test out this patch to see how it
> works on their respective system.  This patch reverts to 2.6.23-rc8
> behaviour of simply truncating the map, but still makes e801/88 info
> available to the kernel; this hopefully should match 2.6.22 behaviour.

Breaks on the Geode - original behavior.

I think that having boot_prams.e820_entries != 0 makes the kernel
assume the e820 data is correct.

> I want to emphasize that this is seriously broken.  Using a partial e820
> map could have disastrous results, since the kernel will have partial
> memory map information and not know about reserved areas, etc.  Part of
> me feels that the right thing to do is what the current git kernel does
> -- either fall back to e801, or stop and error.

I'm inclined to agree.  

Jordan


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