linux-kernel - Re: [PATCH 2/2] powerpc/iommu: check dev->iommu_group before remove a device from iommu

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Date:	Thu, 22 Aug 2013 15:52:37 +0800
From:	Wei Yang <weiyang@...ux.vnet.ibm.com>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
	benh@....ibm.com, paulus@....ibm.com, alex.williamson@...hat.com
Subject: Re: [PATCH 2/2] powerpc/iommu: check dev->iommu_group before remove
 a device from iommu_group

On Thu, Aug 22, 2013 at 05:23:34PM +1000, Alexey Kardashevskiy wrote:
>On 08/19/2013 11:55 AM, Wei Yang wrote:
>> On Mon, Aug 19, 2013 at 11:39:49AM +1000, Alexey Kardashevskiy wrote:
>>> On 08/19/2013 11:29 AM, Wei Yang wrote:
>>>> On Fri, Aug 16, 2013 at 08:15:36PM +1000, Alexey Kardashevskiy wrote:
>>>>> On 08/16/2013 08:08 PM, Wei Yang wrote:
>>>>>> ---
>>>>>>  arch/powerpc/kernel/iommu.c |    3 ++-
>>>>>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>>>>>
>>>>>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>>>>>> index b20ff17..5abf7c3 100644
>>>>>> --- a/arch/powerpc/kernel/iommu.c
>>>>>> +++ b/arch/powerpc/kernel/iommu.c
>>>>>> @@ -1149,7 +1149,8 @@ static int iommu_bus_notifier(struct notifier_block *nb,
>>>>>>  	case BUS_NOTIFY_ADD_DEVICE:
>>>>>>  		return iommu_add_device(dev);
>>>>>>  	case BUS_NOTIFY_DEL_DEVICE:
>>>>>> -		iommu_del_device(dev);
>>>>>> +		if (dev->iommu_group)
>>>>>> +			iommu_del_device(dev);
>>>>>>  		return 0;
>>>>>>  	default:
>>>>>>  		return 0;
>>>>>>
>>>>>
>>>>> This one seems redundant, no?
>>>>
>>>> Sorry for the late.
>>>>
>>>> Yes, these two patches have the same purpose to guard the system, while in two
>>>> different places.  One is in powernv platform, the other is in the generic iommu 
>>>> driver.
>>>>
>>>> The one in powernv platform is used to correct the original logic.
>>>>
>>>> The one in generic iommu driver is to keep system safe in case other platform to
>>>> call iommu_group_remove_device() without the check.
>>>
>>>
>>> But I am moving bus notifier to powernv code (posted a patch last week,
>>> otherwise Freescale's IOMMU conflicted) so this won't be the case.
>> 
>> Yes, I see the patch.
>> 
>> This means other platforms, besides powernv, will check the dev->iommu_group
>> before remove the device? This would be a convention?
>> 
>> If this is the case, the second patch is enough. We don't need to check it in
>> generic iommu driver.
>> 
>> Since I am not very familiar with the code convention, I post these two
>> patches together. This doesn't mean I need to push both of them. Your comments
>> are welcome, lets me understand which one is more suitable in this case.
>
>
>Ok. So. I included the check in the bus notifier which I moved to powernv
>platform, I guess I'll repost the series soon.

Thanks, this check will guard the powernv platform.

>
>Good luck with pushing the fix for drivers/iommu/iommu.c :)
>

Alex,

Sorry for not including you in the very beginning, which may spend you more
efforts to track previous mails in this thread.

Do you think it is reasonable to check the dev->iommu_group in
iommu_group_remove_device()? Or we can count on the bus notifier to check it?

Welcome your suggestions~

>
>
>-- 
>Alexey

-- 
Richard Yang
Help you, Help me

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