Re: git-latest: kernel oops in IOMMU setup

["Zhao, Yu" <yu.zhao@intel.com>]

Dirk Hohndel wrote:
> On Sat, 10 Jan 2009 00:16:22 +0800
> "Zhao, Yu" <yu.zhao@intel.com> wrote:
> 
>> Dirk Hohndel wrote:
>>> On Fri, 9 Jan 2009 14:53:14 +0800
>>> "Han, Weidong" <weidong.han@intel.com> wrote:
>>>
>>>> Dirk Hohndel wrote:
>>>>> On Thu, 8 Jan 2009 18:05:15 -0800
>>>>> Dirk Hohndel <hohndel@infradead.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@linux.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@intel.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

The laptop has a nasty bios, try to update it if you want to get rid of 
these noises... assuming you are luck enough :-)