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

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Message-ID: <49677856.90807@intel.com>
Date:	Sat, 10 Jan 2009 00:16:22 +0800
From:	"Zhao, Yu" <yu.zhao@...el.com>
To:	Dirk Hohndel <hohndel@...radead.org>
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

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>
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