Re: [PATCH v5 01/14] iommu: Add dma ownership management interfaces

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

Hi Christoph,

On 1/4/22 6:08 PM, Christoph Hellwig wrote:
> On Tue, Jan 04, 2022 at 09:56:31AM +0800, Lu Baolu wrote:
>> Multiple devices may be placed in the same IOMMU group because they
>> cannot be isolated from each other. These devices must either be
>> entirely under kernel control or userspace control, never a mixture.
>>
>> This adds dma ownership management in iommu core and exposes several
>> interfaces for the device drivers and the device userspace assignment
>> framework (i.e. vfio), so that any conflict between user and kernel
>> controlled DMA could be detected at the beginning.
>>
>> The device driver oriented interfaces are,
>>
>> 	int iommu_device_use_dma_api(struct device *dev);
>> 	void iommu_device_unuse_dma_api(struct device *dev);
>>
>> Devices under kernel drivers control must call iommu_device_use_dma_api()
>> before driver probes. The driver binding process must be aborted if it
>> returns failure.
>>
>> The vfio oriented interfaces are,
>>
>> 	int iommu_group_set_dma_owner(struct iommu_group *group,
>> 				      void *owner);
>> 	void iommu_group_release_dma_owner(struct iommu_group *group);
>> 	bool iommu_group_dma_owner_claimed(struct iommu_group *group);
>>
>> The device userspace assignment must be disallowed if the set dma owner
>> interface returns failure.
>>
>> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
>> Signed-off-by: Kevin Tian <kevin.tian@intel.com>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   include/linux/iommu.h |  31 ++++++++
>>   drivers/iommu/iommu.c | 161 +++++++++++++++++++++++++++++++++++++++++-
>>   2 files changed, 189 insertions(+), 3 deletions(-)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index de0c57a567c8..568f285468cf 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -682,6 +682,13 @@ struct iommu_sva *iommu_sva_bind_device(struct device *dev,
>>   void iommu_sva_unbind_device(struct iommu_sva *handle);
>>   u32 iommu_sva_get_pasid(struct iommu_sva *handle);
>>   
>> +int iommu_device_use_dma_api(struct device *dev);
>> +void iommu_device_unuse_dma_api(struct device *dev);
>> +
>> +int iommu_group_set_dma_owner(struct iommu_group *group, void *owner);
>> +void iommu_group_release_dma_owner(struct iommu_group *group);
>> +bool iommu_group_dma_owner_claimed(struct iommu_group *group);
>> +
>>   #else /* CONFIG_IOMMU_API */
>>   
>>   struct iommu_ops {};
>> @@ -1082,6 +1089,30 @@ static inline struct iommu_fwspec *dev_iommu_fwspec_get(struct device *dev)
>>   {
>>   	return NULL;
>>   }
>> +
>> +static inline int iommu_device_use_dma_api(struct device *dev)
>> +{
>> +	return 0;
>> +}
>> +
>> +static inline void iommu_device_unuse_dma_api(struct device *dev)
>> +{
>> +}
>> +
>> +static inline int
>> +iommu_group_set_dma_owner(struct iommu_group *group, void *owner)
>> +{
>> +	return -ENODEV;
>> +}
>> +
>> +static inline void iommu_group_release_dma_owner(struct iommu_group *group)
>> +{
>> +}
>> +
>> +static inline bool iommu_group_dma_owner_claimed(struct iommu_group *group)
>> +{
>> +	return false;
>> +}
>>   #endif /* CONFIG_IOMMU_API */
>>   
>>   /**
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 8b86406b7162..ff0c8c1ad5af 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -48,6 +48,8 @@ struct iommu_group {
>>   	struct iommu_domain *default_domain;
>>   	struct iommu_domain *domain;
>>   	struct list_head entry;
>> +	unsigned int owner_cnt;
>> +	void *owner;
>>   };
>>   
>>   struct group_device {
>> @@ -289,7 +291,12 @@ int iommu_probe_device(struct device *dev)
>>   	mutex_lock(&group->mutex);
>>   	iommu_alloc_default_domain(group, dev);
>>   
>> -	if (group->default_domain) {
>> +	/*
>> +	 * If device joined an existing group which has been claimed
>> +	 * for none kernel DMA purpose, avoid attaching the default
>> +	 * domain.
>> +	 */
>> +	if (group->default_domain && !group->owner) {
>>   		ret = __iommu_attach_device(group->default_domain, dev);
>>   		if (ret) {
>>   			mutex_unlock(&group->mutex);
>> @@ -2320,7 +2327,7 @@ static int __iommu_attach_group(struct iommu_domain *domain,
>>   {
>>   	int ret;
>>   
>> -	if (group->default_domain && group->domain != group->default_domain)
>> +	if (group->domain && group->domain != group->default_domain)
>>   		return -EBUSY;
>>   
>>   	ret = __iommu_group_for_each_dev(group, domain,
>> @@ -2357,7 +2364,11 @@ static void __iommu_detach_group(struct iommu_domain *domain,
>>   {
>>   	int ret;
>>   
>> -	if (!group->default_domain) {
>> +	/*
>> +	 * If group has been claimed for none kernel DMA purpose, avoid
>> +	 * re-attaching the default domain.
>> +	 */
> 
> none kernel reads odd.  But maybe drop that and just say 'claimed
> already' ala:
> 
> 	/*
> 	 * If the group has been claimed already, do not re-attach the default
> 	 * domain.
> 	 */
> 

Sure!

Best regards,
baolu