linux-kernel - Re: WARNING: at drivers/iommu/dmar.c:484 warn_invalid

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Message-ID: <20130710000511.GC2676@sequoia2.sous-sol.org>
Date:	Tue, 9 Jul 2013 17:05:11 -0700
From:	Chris Wright <chrisw@...s-sol.org>
To:	Guenter Roeck <linux@...ck-us.net>
Cc:	Chris Wright <chrisw@...s-sol.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux-foundation.org>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: WARNING: at drivers/iommu/dmar.c:484 warn_invalid_dmar with
 Intel Motherboard

* Guenter Roeck (linux@...ck-us.net) wrote:
> On Tue, Jul 09, 2013 at 04:22:52PM -0700, Chris Wright wrote:
> > * Guenter Roeck (linux@...ck-us.net) wrote:
> > > On Tue, Jul 09, 2013 at 03:05:39PM -0600, Bjorn Helgaas wrote:
> > > > [+cc Joerg, David, iommu list]
> > > > 
> > > > On Tue, Jul 9, 2013 at 2:24 PM, Guenter Roeck <linux@...ck-us.net> wrote:
> > > > > I started seeing this problem after updating the BIOS trying fix another issue,
> > > > > though I may have missed it earlier.
> > > > >
> > > > > I understand this is a BIOS bug. Would be great if someone can pass this on
> > > > > to Intel BIOS engineers.
> > > > 
> > > > Maybe.  It'd be nice if Linux handled it better, though.
> > > > 
> > > If anyone has an idea how to do that, I'll be happy to write a patch.
> > 
> > I'm not sure there's much you can do.  The BIOS is saying there's a DMAR
> > unit, and then saying the registers are at addr 0x0.  The kernel is
> > simply warning you about the invalid DMAR table entry.
> > 
> > One thing I've seen is the BIOS zeroing the base register address when
> > VT-d is disabled in BIOS.  So, Guenter, a "fix" may be simply enabling
> > VT-d in the BIOS.
>
> Ah, yes, I think I may have that disabled. I'll check it tonight.
> 
> Does that really warrant a traceback, or would a warning message be more
> appropriate (possibly telling the user to enable VT-d) ?

Bottom line, the BIOS is providing what we're seeing as invalid tables.
If it's a BIOS attempt to disable VT-d is hard to glean from invalid
tables, and not all BIOS give interface to enable/disable VT-d.

It is a warning message, BTW.  Guess I'd be inclined to leave as it is.

thanks,
-chris
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