Re: [PATCH v3 2/4] iommu: Add iommu_aux_at(de)tach_group()

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Jacob,

On 7/16/20 12:01 AM, Jacob Pan wrote:
> On Wed, 15 Jul 2020 08:47:36 +0800
> Lu Baolu <baolu.lu@linux.intel.com> wrote:
> 
>> Hi Jacob,
>>
>> On 7/15/20 12:39 AM, Jacob Pan wrote:
>>> On Tue, 14 Jul 2020 13:57:01 +0800
>>> Lu Baolu<baolu.lu@linux.intel.com>  wrote:
>>>    
>>>> This adds two new aux-domain APIs for a use case like vfio/mdev
>>>> where sub-devices derived from an aux-domain capable device are
>>>> created and put in an iommu_group.
>>>>
>>>> /**
>>>>    * iommu_aux_attach_group - attach an aux-domain to an iommu_group
>>>> which
>>>>    *                          contains sub-devices (for example
>>>> mdevs) derived
>>>>    *                          from @dev.
>>>>    * @domain: an aux-domain;
>>>>    * @group:  an iommu_group which contains sub-devices derived from
>>>> @dev;
>>>>    * @dev:    the physical device which supports IOMMU_DEV_FEAT_AUX.
>>>>    *
>>>>    * Returns 0 on success, or an error value.
>>>>    */
>>>> int iommu_aux_attach_group(struct iommu_domain *domain,
>>>>                              struct iommu_group *group,
>>>>                              struct device *dev)
>>>>
>>>> /**
>>>>    * iommu_aux_detach_group - detach an aux-domain from an
>>>> iommu_group *
>>>>    * @domain: an aux-domain;
>>>>    * @group:  an iommu_group which contains sub-devices derived from
>>>> @dev;
>>>>    * @dev:    the physical device which supports IOMMU_DEV_FEAT_AUX.
>>>>    *
>>>>    * @domain must have been attached to @group via
>>>> iommu_aux_attach_group(). */
>>>> void iommu_aux_detach_group(struct iommu_domain *domain,
>>>>                               struct iommu_group *group,
>>>>                               struct device *dev)
>>>>
>>>> It also adds a flag in the iommu_group data structure to identify
>>>> an iommu_group with aux-domain attached from those normal ones.
>>>>
>>>> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>
>>>> ---
>>>>    drivers/iommu/iommu.c | 58
>>>> +++++++++++++++++++++++++++++++++++++++++++ include/linux/iommu.h |
>>>> 17 +++++++++++++ 2 files changed, 75 insertions(+)
>>>>
>>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>>> index e1fdd3531d65..cad5a19ebf22 100644
>>>> --- a/drivers/iommu/iommu.c
>>>> +++ b/drivers/iommu/iommu.c
>>>> @@ -45,6 +45,7 @@ struct iommu_group {
>>>>    	struct iommu_domain *default_domain;
>>>>    	struct iommu_domain *domain;
>>>>    	struct list_head entry;
>>>> +	unsigned int aux_domain_attached:1;
>>>>    };
>>>>    
>>>>    struct group_device {
>>>> @@ -2759,6 +2760,63 @@ int iommu_aux_get_pasid(struct iommu_domain
>>>> *domain, struct device *dev) }
>>>>    EXPORT_SYMBOL_GPL(iommu_aux_get_pasid);
>>>>    
>>>> +/**
>>>> + * iommu_aux_attach_group - attach an aux-domain to an iommu_group
>>>> which
>>>> + *                          contains sub-devices (for example
>>>> mdevs) derived
>>>> + *                          from @dev.
>>>> + * @domain: an aux-domain;
>>>> + * @group:  an iommu_group which contains sub-devices derived from
>>>> @dev;
>>>> + * @dev:    the physical device which supports IOMMU_DEV_FEAT_AUX.
>>>> + *
>>>> + * Returns 0 on success, or an error value.
>>>> + */
>>>> +int iommu_aux_attach_group(struct iommu_domain *domain,
>>>> +			   struct iommu_group *group, struct
>>>> device *dev) +{
>>>> +	int ret = -EBUSY;
>>>> +
>>>> +	mutex_lock(&group->mutex);
>>>> +	if (group->domain)
>>>> +		goto out_unlock;
>>>> +
>>> Perhaps I missed something but are we assuming only one mdev per
>>> mdev group? That seems to change the logic where vfio does:
>>> iommu_group_for_each_dev()
>>> 	iommu_aux_attach_device()
>>>    
>>
>> It has been changed in PATCH 4/4:
>>
>> static int vfio_iommu_attach_group(struct vfio_domain *domain,
>>                                      struct vfio_group *group)
>> {
>>           if (group->mdev_group)
>>                   return iommu_aux_attach_group(domain->domain,
>>                                                 group->iommu_group,
>>                                                 group->iommu_device);
>>           else
>>                   return iommu_attach_group(domain->domain,
>> group->iommu_group);
>> }
>>
>> So, for both normal domain and aux-domain, we use the same concept:
>> attach a domain to a group.
>>
> I get that, but don't you have to attach all the devices within the

This iommu_group includes only mediated devices derived from an
IOMMU_DEV_FEAT_AUX-capable device. Different from iommu_attach_group(),
iommu_aux_attach_group() doesn't need to attach the domain to each
device in group, instead it only needs to attach the domain to the
physical device where the mdev's were created from.

> group? Here you see the group already has a domain and exit.

If the (group->domain) has been set, that means a domain has already
attached to the group, so it returns -EBUSY.

Best regards,
baolu
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