Re: [PATCH RFC 03/11] iommu: Add attach/detach_dev_pasid domain ops

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

On 2022/3/21 15:13, Tian, Kevin wrote:
>> From: Lu Baolu<baolu.lu@linux.intel.com>
>> Sent: Sunday, March 20, 2022 2:40 PM
>>
>> Attaching an IOMMU domain to a PASID of a device is a generic operation
>> for modern IOMMU drivers which support PASID-granular DMA address
>> translation. Currently visible usage scenarios include (but not limited):
>>
>>   - SVA
>>   - kernel DMA with PASID
>>   - hardware-assist mediated device
>>
>> This adds a pair of common domain ops for this purpose and implements a
>> couple of wrapper helpers for in-kernel usage.
>>
>> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>
>> ---
>>   include/linux/iommu.h | 22 ++++++++++++++++++++++
>>   drivers/iommu/iommu.c | 41
>> +++++++++++++++++++++++++++++++++++++++++
>>   2 files changed, 63 insertions(+)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 3e179b853380..e51845b9a146 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -268,6 +268,8 @@ struct iommu_ops {
>>    * struct iommu_domain_ops - domain specific operations
>>    * @attach_dev: attach an iommu domain to a device
>>    * @detach_dev: detach an iommu domain from a device
>> + * @attach_dev_pasid: attach an iommu domain to a pasid of device
>> + * @detach_dev_pasid: detach an iommu domain from a pasid of device
>>    * @map: map a physically contiguous memory region to an iommu domain
>>    * @map_pages: map a physically contiguous set of pages of the same size
>> to
>>    *             an iommu domain.
>> @@ -285,6 +287,10 @@ struct iommu_ops {
>>   struct iommu_domain_ops {
>>   	int (*attach_dev)(struct iommu_domain *domain, struct device *dev);
>>   	void (*detach_dev)(struct iommu_domain *domain, struct device
>> *dev);
>> +	int (*attach_dev_pasid)(struct iommu_domain *domain,
>> +				struct device *dev, ioasid_t id);
>> +	void (*detach_dev_pasid)(struct iommu_domain *domain,
>> +				 struct device *dev, ioasid_t id);
>>
>>   	int (*map)(struct iommu_domain *domain, unsigned long iova,
>>   		   phys_addr_t paddr, size_t size, int prot, gfp_t gfp);
>> @@ -678,6 +684,11 @@ int iommu_group_claim_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);
>>
>> +int iommu_attach_device_pasid(struct iommu_domain *domain,
>> +			      struct device *dev, ioasid_t pasid);
>> +void iommu_detach_device_pasid(struct iommu_domain *domain,
>> +			       struct device *dev, ioasid_t pasid);
>> +
>>   #else /* CONFIG_IOMMU_API */
>>
>>   struct iommu_ops {};
>> @@ -1046,6 +1057,17 @@ static inline bool
>> iommu_group_dma_owner_claimed(struct iommu_group *group)
>>   {
>>   	return false;
>>   }
>> +
>> +static inline int iommu_attach_device_pasid(struct iommu_domain
>> *domain,
>> +					    struct device *dev, ioasid_t pasid)
>> +{
>> +	return -ENODEV;
>> +}
>> +
>> +static inline void iommu_detach_device_pasid(struct iommu_domain
>> *domain,
>> +					     struct device *dev, ioasid_t pasid)
>> +{
>> +}
>>   #endif /* CONFIG_IOMMU_API */
>>
>>   /**
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 0c42ece25854..78c71ee15f36 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -3167,3 +3167,44 @@ bool iommu_group_dma_owner_claimed(struct
>> iommu_group *group)
>>   	return user;
>>   }
>>   EXPORT_SYMBOL_GPL(iommu_group_dma_owner_claimed);
>> +
>> +int iommu_attach_device_pasid(struct iommu_domain *domain,
>> +			      struct device *dev, ioasid_t pasid)
>> +{
>> +	struct iommu_group *group;
>> +	int ret = -EINVAL;
>> +
>> +	if (!domain->ops->attach_dev_pasid)
>> +		return -EINVAL;
>> +
>> +	group = iommu_group_get(dev);
>> +	if (!group)
>> +		return -ENODEV;
>> +
>> +	mutex_lock(&group->mutex);
>> +	if (iommu_group_device_count(group) != 1)
>> +		goto out_unlock;
> Need move the reason of above limitation from iommu_sva_bind_device()
> to here:
> 
> 	/*
> 	 * To keep things simple, SVA currently doesn't support IOMMU groups
> 	 * with more than one device. Existing SVA-capable systems are not
> 	 * affected by the problems that required IOMMU groups (lack of ACS
> 	 * isolation, device ID aliasing and other hardware issues).
> 	 */
> 	if (iommu_group_device_count(group) != 1)
> 		goto out_unlock;

Yes. We need a comment around this code. But it's not only for SVA but
also for all pasid attachment feature. I need more inputs to judge
whether this limitation is reasonable.

> 
> btw I didn't see any safeguard on above assumption in device hotplug path
> to a group which already has SVA enabled...
> 

Agreed.

Best regards,
baolu