Re: [Qemu-devel] [PATCH v9 04/12] vfio iommu: Add support for mediated devices

[Kirti Wankhede]

On 10/21/2016 8:06 PM, Alex Williamson wrote:
> On Fri, 21 Oct 2016 15:49:07 +0800
> Jike Song <address@hidden> 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