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

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Date:	Mon, 19 Aug 2013 09:55:38 +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
Subject: Re: [PATCH 2/2] powerpc/iommu: check dev->iommu_group before remove
 a device from iommu_group

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.

>
>
>
>-- 
>Alexey

-- 
Richard Yang
Help you, Help me

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