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

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Message-ID: <20130709234331.GA10833@roeck-us.net>
Date:	Tue, 9 Jul 2013 16:43:31 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Chris Wright <chrisw@...s-sol.org>
Cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	David Woodhouse <dwmw2@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"open list:INTEL IOMMU (VT-d)" <iommu@...ts.linux-foundation.org>
Subject: Re: WARNING: at drivers/iommu/dmar.c:484 warn_invalid_dmar with
 Intel Motherboard

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) ?

Thanks,
Guenter
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