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

[Vasant Hegde <vasant.hegde@amd.com>]

Jason,

On 8/7/2024 11:59 PM, 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.

Oh yeah. uAPI is always tricky. No harm in adding extra flag in advance. I will
update the patch.

-Vasant

> 
>> @Baolu, Do we need to make any changes to intel driver?
> 
> I think Intel ignores this issue, they have nice HW and their RID can
> use both of their supported domain formats in all cases.
> 
> Jason