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

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

Jason,


On 8/9/2024 7:14 PM, Jason Gunthorpe wrote:
> On Fri, Aug 09, 2024 at 12:13:47PM +0530, Vasant Hegde wrote:
>> Jason,
>>
>>
>> On 8/8/2024 6:38 PM, Jason Gunthorpe wrote:
>>> On Wed, Aug 07, 2024 at 10:16:29PM -0300, Jason Gunthorpe wrote:
>>>> On Wed, Aug 07, 2024 at 03:29:47PM -0300, Jason Gunthorpe wrote:
>>>>>> @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.
>>>>
>>>> On second thought it does need to accept, but ignore the new flags..
>>>
>>> And probably HW that does not support PASID should reject the
>>> IOMMU_HWPT_ALLOC_PASID flag at least.
>>
>>
>> You mean error out if IOMMU or device doesnot support PASID?
> 
> Just the iommu, yes.
> 
> Like in AMD terms if there is no AMDv2 page table support then fail
> it.
> 
>>> Maybe IOMMU_HWPT_ALLOC_DEV_PASID can be reasonably ignored if the HW
>>> doesn't support PASID.
>>  
>> You mean make it as optional flag? Meaning if HW doesn't support PASID then
>> still allocate a domain without PASID capability?
> 
> Yes, for the RID domain it seems harmless to ignore, I'm not really
> sure on this though.
> 
> Otherwise we'd want to report pasid support through a INFO return so
> userspace knows if it should specify this flag.

Let me summarize and see if I got everything right.

- Enhance iommufd_get_hw_info ioctl to get device PASID capability
  HW driver will implement iommu_ops->capable() to check PASID capability

- Userspace will use above info and calls iommu_ops->domain_alloc_user() with
  appropriate flag (If PASID capability present then pass
  IOMMU_HWPT_ALLOC_DEV_PASID as flag).

- HW driver : If IOMMU and dev supports PASID then allocate PASID capable
  domain, else allocate normal domain.

- When attaching PASID to device (RID), PASID attachment will pass only domain
supports PASID, else it will fail.

- IOMMU_HWPT_ALLOC_PASID  flag is optional:
  If we endup implementing this flag, then it will allocate PASID capable domain
if HW IOMMU supports it (It will not check device capability).


Does this flow makes sense?

-Vasant