Re: [PATCH v3 00/12] iommu: Domain allocation enhancements

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

On 2024/10/17 22:01, Vasant Hegde wrote:
> This series adds iommu_paging_domain_alloc_flags() which takes flags to
> pass additional details for domain allocation (like domain with PASID
> support). Also adjusts core code to handler variuos domain allocations.
> 
> Also updates AMD IOMMU driver domain allocation code. With this by
> default it will allocate domain with V2 page table for PASID capable
> device and v1 page table for rest of the devices.
> 
> 
> TODO:
> @Jason, @Kevin, @Baolu,
>    With this series if driver implements domain_alloc_user() then we assume
>    IOMMU always supports PASID. If IOMMU doesn't support PASID (ex: AMD driver

I don't think this assumption is true for all iommu drivers. In my
opinion, domain_alloc_user() will eventually be a common callback used
by the iommu core to allocate paging domains. It includes an allocation
flag that specifies various requirements, including PASID, which is a
special requirement for the amd iommu driver.

>    not supporting V2 page table) and device is PASID capable, then driver will
>    return error. Device probe will fail.
> 
>    I think if driver return error, core layer should retry without
>    IOMMU_HWPT_ALLOC_PASID flag. Other option is indivisual driver in error path
>    of domain_alloc_user allocating non-PASID capable domain.
> 
>    I prefer first option. Just wanted to discuss before implementing. Any preferred
>    option here? OR any other better way to solve this?
> 
> 
> Note :
>    vt-d specific changes is handled in separate series [1].
> 
> [1]https://lore.kernel.org/linux-iommu/20241011042722.73930-8- 
> baolu.lu@linux.intel.com/
> 
> @Baolu,
>    Do you want me to include above patch in this series so that it doesn't break intel driver?

I haven't read through the whole series yet, but let's avoid creating
unnecessary dependencies.

Thanks,
baolu