Re: [RFC] iommu_ops->domain_alloc_paging() enhancement to support AMD IOMMU driver

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

On 7/11/24 9:56 PM, Yi Liu wrote:
> 
>> For UNMANAGED domain (like vfio-pci), we would need a indication from 
>> core layer
>> saying whether we want to allocate PASID capable domain or not. So that
>> internally we can allocate appropriate page table type.
>>
>> That means from VFIO layer we need to pass this detail to IOMMU layer.
>> For this part, I will start watching your patch. May be we can start 
>> discussion
>> in that thread itself.
>>
> 
> yeah. Looks like you need to pass a hint to iommu driver for domain
> allocation. For the usage vfio+iommufd, it is fine as the domain_alloc_user
> accepts a flag. For legacy vfio (using vfio iommu type1) usage, it's a bit
> tough as the domain allocation is within kernel, userspace does not have
> any input on it so far. And vfio type1 does not expose the domain concept
> to userspace, it only exposes container which is kind of an address space
> object. This means no good way for userspace to control the domain
> allocation.
> 
> If it's only a matter when PASID is enabled, perhaps we can skip vfio iommu
> type1 as it is not supposed to support PASID.

As we have already agreed that new features should go through IOMMUFD
and vfio/type1 is only kept for legacy compatible purpose, I don't think
we need to carry any PASID bits in the vifo path. Did I miss anything?

Thanks,
baolu