Re: [PATCH RFCv2] iommu: Add domain type and flag to domain_alloc_paging()

[Yi Liu <yi.l.liu@intel.com>]

On 2024/8/8 02:29, Jason Gunthorpe wrote:
> On Wed, Aug 07, 2024 at 10:22:00PM +0530, Vasant Hegde wrote:
>>> Needs more words, maybe even two flags?
>>>
>>>   @IOMMU_HWPT_ALLOC_DEV_PASID: When the domain is used on a device,
>>>   with no PASID, the device will support later attaching a PASID as
>>>   well. Some HW requires a specific domain format on the device to
>>>   allow PASID to work.
>>
>> I will add this.
>>
>>>   @IOMMU_HWPT_ALLOC_PASID: The domain can be used as a PASID. The
>>>   domain attached to the device must have also been allocated with
>>>   IOMMU_HWPT_ALLOC_DEV_PASID.
>>
>> Why do we need this flag? Previous one is already allocated PASID capable
>> domain. Is this similar to SVA domain?
> 
> IOMMU_HWPT_ALLOC_DEV_PASID is the flag you specify to allocate the
> domain you will attach to the RID
> 
> IOMMU_HWPT_ALLOC_PASID is the flag you specify if you intend to attach
> this domain to a PASID
> 
> They are actually different operations from a user perspective. Today
> every iommu driver implements them with the same logic..
> 
> So I thought perhaps they should be seperate, at least if we get some
> really crazy HW down the road the uAPI will still work. uAPI is a bit
> more tricky because you can't change it.

Hi Jason,

could you map the above two flags to the actual usage a bit? I'm not
quite getting why we need two flags here as well. :(

-- 
Regards,
Yi Liu