linux-kernel - Re: Bug#584846: Detects only 64MB and fails to boot on Intel Green City board if e820 hooked by GRUB2

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Message-ID: <20100613000742.GA3469@feather>
Date:	Sat, 12 Jun 2010 17:07:43 -0700
From:	Josh Triplett <josh@...htriplett.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Ben Hutchings <ben@...adent.org.uk>, x86@...nel.org,
	584846@...s.debian.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: Bug#584846: Detects only 64MB and fails to boot on Intel Green
 City board if e820 hooked by GRUB2

On Sat, Jun 12, 2010 at 04:02:44PM -0700, H. Peter Anvin wrote:
> On 06/12/2010 03:26 PM, Josh Triplett wrote:
> > 
> > Everything looks identical except for the region GRUB hooked right below
> > the first reserved region; the unhooked version has available memory
> > from 0-0x9cbf0, and the hooked version has available memory from
> > 0-0x9cba0, then reserved from 0x9cba0-0x9cbec, then 4 bytes of available
> > memory, and then the same reserved region as before.
> 
> Actually... are both these done by chainloading Grub (with and without
> mapping), or is the unhooked done without chainloading Grub at all?
> 
> To me it looks like something is chaining INT 15h even in the
> "unchained" case...

The "unhooked" case still chainloaded from GRUB, just without calling
drivemap and thus without hooking anything.  I can test without
chainloading from GRUB, though to the best of my knowledge GRUB doesn't
hook int 15 unless it needs to intercept e820 (and e801 and 88).

- Josh Triplett
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