Re: [PATCH 1/5] iommu: Enhance domain allocation code to take additional flags

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

On 8/22/24 12:31 AM, Jason Gunthorpe wrote:
>>    I think instead of having separate function it may be better to
>>    enhance __iommu_domain_alloc() such that:
>>      - Keep below changes from this patch
>>        - iommu_domain_init()
>>        - iommu_get_dma_cookie call inside iommu_setup_default_domain()
>>      - modify __iommu_domain_alloc() to additional param (flags)
>>      - iommu_paging_domain_alloc_flags() will call __iommu_domain_alloc()
> My expectation was to basically remove iommu_domain_alloc() entirely
> once Lu's work is merged.
> 
> Instead we'd have these direct APIs:
>    iommu_domain_alloc_paging_flags()

Is it possible to use different domain allocation APIs for kernel DMA
and user-space DMA? Right now, we differentiate between these two types
of domains using IOMMU_DOMAIN_DMA and IOMMU_DOMAIN_UNMANAGED.

I'm thinking about this because the Intel iommu driver has a similar
need to AMD. They both recommend using different page table formats for
IOMMU_DOMAIN_DMA and IOMMU_DOMAIN_UNMANAGED, which is currently stopping
us from implementing domain_alloc_paging in the Intel iommu driver.

Thanks,
baolu