Re: [PATCH v6 03/10] iommu: Add attach handle to struct iopf_group

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

On 6/5/24 4:23 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Monday, May 27, 2024 12:05 PM
>>
>> @@ -249,6 +249,12 @@ enum iommu_cap {
>>   	 */
>>   	IOMMU_CAP_DEFERRED_FLUSH,
>>   	IOMMU_CAP_DIRTY_TRACKING,	/* IOMMU supports dirty
>> tracking */
>> +	/*
>> +	 * IOMMU driver supports user-managed IOASID table. There is no
>> +	 * user domain for each PASID and the I/O page faults are forwarded
>> +	 * through the user domain attached to the device RID.
>> +	 */
>> +	IOMMU_CAP_USER_IOASID_TABLE,
>>   };
> 
> Given all other context are around PASID let's just call it as USER_PASID_TABLE.
> 
> btw this goes differently from your plan in [1] which tried to introduce
> different nesting types between Intel and other vendors.
> 
> I guess the reason might be that you want to avoid getting the handle
> for RID on Intel platform in case of failing to find the handle for the
> faulting PASID. and save a new domain type.
> 
> this looks fine to me but should be explained.

Yeah! I was considering this in two aspects and chose this simple
solution in the end.

- If we choose to add a new domain type, we need to change iommufd,
   iommu core and the individual driver. That seems too complicated to
   address a small issue here.

- Fundamentally, this is a hardware implementation difference, hence use
   the existing per-device iommu capability interface sounds more
   reasonable.

> 
> [1] https://lore.kernel.org/linux-iommu/0de7c71f-571a-4800-8f2b-9eda0c6b75de@linux.intel.com/
> 

Best regards,
baolu