linux-kernel - Re: git-latest: kernel oops in IOMMU setup

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Date:	Fri, 9 Jan 2009 08:34:35 -0800
From:	Dirk Hohndel <hohndel@...radead.org>
To:	"Zhao, Yu" <yu.zhao@...el.com>
Cc:	"Han, Weidong" <weidong.han@...el.com>,
	'Grant Grundler' <grundler@...isc-linux.org>,
	"'linux-pci@...r.kernel.org'" <linux-pci@...r.kernel.org>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>,
	'Jesse Barnes' <jbarnes@...tuousgeek.org>,
	"'iommu@...ts.linux-foundation.org'" 
	<iommu@...ts.linux-foundation.org>, 'Ingo Molnar' <mingo@...e.hu>,
	'Arjan van de Ven' <arjan@...radead.org>
Subject: Re: git-latest: kernel oops in IOMMU setup

On Sat, 10 Jan 2009 00:16:22 +0800
"Zhao, Yu" <yu.zhao@...el.com> wrote:

> Dirk Hohndel wrote:
> > On Fri, 9 Jan 2009 14:53:14 +0800
> > "Han, Weidong" <weidong.han@...el.com> wrote:
> > 
> >> Dirk Hohndel wrote:
> >>> On Thu, 8 Jan 2009 18:05:15 -0800
> >>> Dirk Hohndel <hohndel@...radead.org> wrote:
> >>>
> >>>> On Fri, 9 Jan 2009 08:58:46 +0800 "Han, Weidong"
> >>>>
> >>>> I updated to Linus' latest git (as your description made me
> >>>> wonder if the async stuff might play a role here). I still get
> >>>> an oops - but at a different spot and the system no longer hangs
> >>>> - it partly recovers (but things aren't too well - for example
> >>>> my USB keyboard / mouse don't work anymore).
> >>> Spoke too soon. Rebooted and had the same hard lockup again. This
> >>> time I had my camera within reach, so here's the trace:
> >>>
> >>> device_to_iommu+0x33/0x73
> >>> domain_context_mapping_one+0x37/0x335
> >>> domain_context_mapping+0x25/0xa7
> >>> iommu_prepare_identity+0xd7/0xf3
> >>> intel_iommu_init+0x4e4/0x8f3
> >>> ? mutex_lock
> >>> ? sysctl_net_init
> >>> ? pci_iommu_init
> >>> pci_iommu_init
> >>>
> >>> I also have stack, code and register values. Let me know if you
> >>> need them. Or I can just post the picture :-)
> >>>
> >>> Again, very latest git tree, VT-d enabled.
> >>>
> >>> /D
> >> I tried latest git tree, it works for me. Above call trace looks
> >> right. 
> > 
> > Spent some more time reading the code. Can't quite claim to
> > understand all of it, yet, but I notice that most everywhere else
> > drhd->devices[i] is checked to be != NULL before it is accessed.
> > Why is it safe not to do that in device_to_iommu()?
> > 
> > Would the patch below be a valid fix? It stops my system from
> > hanging at boot. But I wonder if there is an assertion that if
> > drhd->ignored is 0 then drhd->devices[0..drhd->device_cnt] is known
> > to be != NULL and therefore this test is just hiding a bug
> > somewhere else...
> > 
> > /D
> > 
> > Signed-off-by: Dirk Hohndel <hohndel@...ux.intel.com>
> > ---
> >  drivers/pci/intel-iommu.c |    3 ++-
> >  1 files changed, 2 insertions(+), 1 deletions(-)
> > 
> > diff --git a/drivers/pci/intel-iommu.c b/drivers/pci/intel-iommu.c
> > index 235fb7a..3dfecb2 100644
> > --- a/drivers/pci/intel-iommu.c
> > +++ b/drivers/pci/intel-iommu.c
> > @@ -438,7 +438,8 @@ static struct intel_iommu *device_to_iommu(u8
> > bus, u8 devfn) continue;
> >  
> >  		for (i = 0; i < drhd->devices_cnt; i++)
> > -			if (drhd->devices[i]->bus->number == bus &&
> > +			if (drhd->devices[i] &&
> > +			    drhd->devices[i]->bus->number == bus &&
> >  			    drhd->devices[i]->devfn == devfn)
> >  				return drhd->iommu;
> >  
> 
> Did you see following in the kernel message?
>                  printk(KERN_WARNING PREFIX
>                  "Device scope device [%04x:%02x:%02x.%02x] not
> found\n", segment, scope->bus, path->dev, path->fn);
> 
> If yes, then
> 		Acked-by: Yu Zhao <yu.zhao@...el.com>

Yes,

DMAR: Device scope device [0000:00:03:02] not found
DMAR: Device scope device [0000:00:03:02] not found
DMAR: Device scope device [0000:00:03:03] not found
DMAR: Device scope device [0000:00:03:03] not found

/D

-- 
Dirk Hohndel
Intel Open Source Technology Center
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