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

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

On 2024/8/15 11:28, Vasant Hegde wrote:
> Jason, Kevin,
> 
> 
> On 8/15/2024 4:10 AM, Jason Gunthorpe wrote:
>> On Wed, Aug 14, 2024 at 02:38:58AM +0000, Tian, Kevin wrote:
>>
>>>> Flags = 0 means the domain cannot be attached to a PASID
>>>> Flags = 0 means the domain cannot be attached to the RID while PASID
>>>> is in use
>>>  From my understanding there are only two type of formats so far:
>>>
>>>    - a format only working with RID (V1 in AMD, S2 in ARM)
>>>    - a format working with both RID and PASID (V2 in AMD, S1 in ARM,
>>>     S1/S2 in Intel)
>>>
>>> With that in mind we only need one bit to indicate whether a domain
>>> allows PASID attach. The user learns the PASID capability via
>>> GET_HW_INFO and should set or clear the PASID flag consistently
>>> for all non-nesting domains attached to a same device (RID, or RID+PASID).
>>>
>>> for AMD/ARM this consistency is mandatory as one device can only be
>>> configured to a single format. no mix.
>>>
>>> for Intel there's more flexibility but I don't see a reason to mix S1/S2
>>> between RID and PASID, and now both are fixed to S2 for UNMANAGED.
>>>
>>>> The core code should enforce this rule always.
>>>>
>>>> Above that we minimally need
>>>>
>>>> Flags = IOMMU_HWPT_ALLOC_PASID allows the domain to be attached to a
>>>> PASID
>>>>
>>>> And you need to decide if the RID usage is bundled with the above as
>>>> well.
>>> A single bit IOMMU_HWPT_ALLOC_PASID is what I meant. Setting it
>>> means the domain can be attached to both RID and PASID, i.e. RID
>>> attach is always implied.
>> OK, lets try it like that then
>>
>> I also know of no HW that would need it to be different on the RID
> Ok. Single macro with `IOMMU_HWPT_ALLOC_PASID` which allocates PASID capable
> domain if both IOMMU and device supports the feature. If not allocate normal
> domain -OR- return error?
> 
> Also I would assume we want to enhance iommufd_get_hw_info ioctl to get device
> PASID capability. Is that correct?

I suppose that this also includes converting paging domain to user
domain allocation in VFIO (ideally vhost-vdpa as well), right?

Thanks,
baolu