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

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

Jason,


On 8/17/2024 12:07 AM, Jason Gunthorpe wrote:
> On Fri, Aug 16, 2024 at 01:47:52PM +0530, Vasant Hegde wrote:
>> Jason,
>>
>>
>> On 8/15/2024 7:17 PM, Jason Gunthorpe wrote:
>>> On Thu, Aug 15, 2024 at 12:59:13PM +0800, Baolu Lu wrote:
>>>> I suppose that this also includes converting paging domain to user
>>>> domain allocation in VFIO (ideally vhost-vdpa as well), right?
>>>
>>> Another thought is to add a flag to iommu_paging_domain_alloc()..
>>>
>>> Maybe like the below. The small duplication with
>>> __iommu_domain_alloc() would go away when iommu_domain_alloc() finally
>>> goes, then we'd be able to directly call iommu_paging_domain_alloc().
>>
>> This will work. But we have to define NO_PASID flag and pass it from vfio.
> 
> flags = 0 means NO_PASID
> 
> I didn't show it but the dma api domain's allocation path would have
> to specify IOMMU_HWPT_ALLOC_PASID to make it work.


That's fine. Then in your patch we have to prioritize domain_alloc_user() over
domain_alloc_paging. Change will look something like below (paste the code path
that's changing).


2037 struct iommu_domain *iommu_paging_domain_alloc_flags(struct device *dev,
2038                                                      unsigned int flags)
2039 {
2040         const struct iommu_ops *ops = dev_iommu_ops(dev);
2041         struct iommu_domain *domain;
2042
2043         if (!dev_has_iommu(dev))
2044                 return ERR_PTR(-ENODEV);
2045
2046         if (ops->domain_alloc_user)
2047                 domain = ops->domain_alloc_user(dev, flags, NULL, NULL);
2048         else if (ops->domain_alloc_paging && !flags)
2049                 domain = ops->domain_alloc_paging(dev);


-Vasant