linux-kernel - Re: [PATCH -mm] 1/2: MMCONFIG: validate against ACPI motherboard resources

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Message-id: <4664231A.2040703@shaw.ca>
Date:	Mon, 04 Jun 2007 08:35:06 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Olivier Galibert <galibert@...ox.com>,
	Robert Hancock <hancockr@...w.ca>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH -mm] 1/2: MMCONFIG: validate against ACPI motherboard
 resources

Olivier Galibert wrote:
> On Tue, May 29, 2007 at 10:03:32PM -0600, Robert Hancock wrote:
>> -Validate that the area is reserved even if we read it from the
>> chipset directly and not from the MCFG table. This catches the case
>> where the BIOS didn't set the location properly in the chipset and
>> has mapped it over other things it shouldn't have.
> 
> Just for the record, I still fundamentally disagree with that part.
> You're not catching what you think you're catching, since the chipset
> tells you what it is going to decode as mmconfig, no matter what is
> connected to it.

But we don't - not in the case where it's overlapped some other area 
with the MMCONFIG region. We saw a case of this on some of the Intel 
boards, where the MMCONFIG is a 128MB area at 0xf0000000, and when 
sizing the BARs on a PCI Express video device with a 256MB region, it 
ended up being located momentarily at f0000000-ffffffff, which 
overlapped the MMCONFIG area. That caused MMCONFIG to stop working, so 
apparently on that chipset, PCI Express devices connected to the 
northbridge have a higher decode priority than the MMCONFIG area.

If the BIOS is so screwed up that this becomes an issue, I don't think 
we can sanely try to use the table, since we can't anticipate all the 
potential problems that might result.

-- 
Robert Hancock      Saskatoon, SK, Canada
To email, remove "nospam" from hancockr@...pamshaw.ca
Home Page: http://www.roberthancock.com/

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