linux-kernel - Re: [RFC PATCH] PCI MMCONFIG: add validation against ACPI motherboard resources

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Message-Id: <200705011956.30629.jbarnes@virtuousgeek.org>
Date:	Tue, 1 May 2007 19:56:29 -0700
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	Olivier Galibert <galibert@...ox.com>
Cc:	Robert Hancock <hancockr@...w.ca>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...e.de>, Chuck Ebbert <cebbert@...hat.com>,
	Len Brown <lenb@...nel.org>
Subject: Re: [RFC PATCH] PCI MMCONFIG: add validation against ACPI motherboard resources

On Tuesday, May 01, 2007, Jesse Barnes wrote:
> On Monday, April 30, 2007, Olivier Galibert wrote:
> > On Sun, Apr 29, 2007 at 08:14:37PM -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.  This might be
> > > overly pessimistic - we might be able to instead verify that no
> > > other reserved resources (like chipset registers) are inside this
> > > memory range.
> >
> > I have a fundamental problem with that: you don't validate a higher
> > reliability information against a lower one.  The chipset registers
> > are high reliability.  Modulo unknown hardware erratas and bugs in the
> > code (and accepting f0000000 is in practice a bug in the code, the
> > docs are starting to catch up with it too), the chipset *will* decode
> > mmconfig at the looked up address no matter what.  On the other side,
> > the ACPI data is bios generated, and that is well known to be horribly
> > unreliable.  Hell, if it was reliable we could just use the MFCG ACPI
> > table without questions.
>
> Now that I've read his patch closely I think you're right.
>
> Robert, it looks like you'll trust acpi_table_parse if
> pci_mmcfg_check_hostbridge returns a failure.  I think it should be
> treated with a higher priority.  If pci_mmcfg_check_hostbridge returns a
> failure, there's no way MCFG space can work, so we should disable it
> unconditionally in that case (even if ACPI says "trust me, when have I
> ever lied to you?").
>
> I'm testing it now on my 965...

Bah... nevermind Robert, I see you're doing this already in 
pci_mmcfg_reject_broken.  I'm about to reboot & test now.

Jesse
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