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Subject: Re: [PATCH v9 04/12] vfio iommu: Add support for mediated devices
To: Alex Williamson <alex.williamson@redhat.com>,
        Jike Song <jike.song@intel.com>
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From: Kirti Wankhede <kwankhede@nvidia.com>
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Date: Mon, 24 Oct 2016 16:05:13 +0530
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On 10/21/2016 8:06 PM, Alex Williamson wrote:
> On Fri, 21 Oct 2016 15:49:07 +0800
> Jike Song <jike.song@intel.com> wrote:
> 
>> On 10/18/2016 05:22 AM, Kirti Wankhede wrote:
>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>>> index 2ba19424e4a1..5d67058a611d 100644
>>> --- a/drivers/vfio/vfio_iommu_type1.c
>>> +++ b/drivers/vfio/vfio_iommu_type1.c  
>> [snip]
>>>  static int vfio_iommu_type1_attach_group(void *iommu_data,
>>>  					 struct iommu_group *iommu_group)
>>>  {
>>>  	struct vfio_iommu *iommu = iommu_data;
>>> -	struct vfio_group *group, *g;
>>> +	struct vfio_group *group;
>>>  	struct vfio_domain *domain, *d;
>>>  	struct bus_type *bus = NULL;
>>>  	int ret;
>>> @@ -746,10 +1136,14 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>>>  	mutex_lock(&iommu->lock);
>>>  
>>>  	list_for_each_entry(d, &iommu->domain_list, next) {
>>> -		list_for_each_entry(g, &d->group_list, next) {
>>> -			if (g->iommu_group != iommu_group)
>>> -				continue;
>>> +		if (find_iommu_group(d, iommu_group)) {
>>> +			mutex_unlock(&iommu->lock);
>>> +			return -EINVAL;
>>> +		}
>>> +	}
>>>  
>>> +	if (iommu->local_domain) {
>>> +		if (find_iommu_group(iommu->local_domain, iommu_group)) {
>>>  			mutex_unlock(&iommu->lock);
>>>  			return -EINVAL;
>>>  		}
>>> @@ -769,6 +1163,30 @@ static int vfio_iommu_type1_attach_group(void *iommu_data,
>>>  	if (ret)
>>>  		goto out_free;
>>>  
>>> +	if (IS_ENABLED(CONFIG_VFIO_MDEV) && !iommu_present(bus) &&
>>> +	    (bus == &mdev_bus_type)) {  
>>
>> Hi Kirti,
>>
>> By refering mdev_bus_type directly you are making vfio_iommu_type1.ko depends
>> on mdev.ko, but in Kconfig doesn't guarantee the dependency. For example,
>> if CONFIG_VFIO_IOMMU_TYPE1=y and CONFIG_VFIO_MDEV=m, the building will fail.
> 
> Good point, Jike.  I don't think we want to make existing vfio modules
> dependent on mdev modules.  I wonder if we can lookup the mdev_bus_type
> symbol w/o triggering the module load.  Thanks,
> 

Ok. Modifying the check as below works in above case:

        mdev_bus = symbol_get(mdev_bus_type);

        if (mdev_bus && (bus == mdev_bus) && !iommu_present(bus) ) {
                symbol_put(mdev_bus_type);
                ...
        }

Kirti