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: <4C23C6F0.50206@zytor.com>
Date:	Thu, 24 Jun 2010 13:58:24 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Josh Triplett <josh@...htriplett.org>
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 06/24/2010 12:01 PM, Josh Triplett wrote:
> On Thu, Jun 24, 2010 at 07:18:34AM -0700, H. Peter Anvin wrote:
>> On 06/24/2010 12:27 AM, Josh Triplett wrote:
>>> The following patch fixes GRUB; with this patch, I can reserve memory
>>> (such as with drivemap), boot 2.6.35-rc3 successfully, and it detects
>>> all of my RAM.
>>
>> Congratulations!  You have just committed the single most common BIOS
>> implementation bug.  (Sorry for the sarcasm, but this seems to be a bug
>> that almost everyone who tries to implement BIOS makes at one point or
>> another... even the original IBM BIOS had it in at least one place.)
> 
> And a rather large number of sample interrupt code found on the web,
> including the e820 hook from the version of gPXE/Etherboot that I used
> as an example. :)  Given that I just tested against Linux, which very
> carefully works around that particular BIOS bug, I didn't run into any
> issue.
> 
> So, how high does GRUB's bug ("stc ; iret"/"clc ; iret") rank on the
> list of common BIOS implementation bugs?
> 

Less common, since that one is apparently more obvious to people (you
only have to think one step ahead instead of two steps ahead.)

There is a reason Linux works around this and similar bugs... it truly
is extremely common (and does cause real problems in real code.)

	-hpa

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