Re: [RFC PATCH v3 10/10] iommu/sva: Add support for private PASIDs

[Jordan Crouse <jcrouse@codeaurora.org>]

On Thu, Sep 20, 2018 at 06:00:46PM +0100, Jean-Philippe Brucker wrote:
> Provide an API for allocating PASIDs and populating them manually. To ease
> cleanup and factor allocation code, reuse the io_mm structure for private
> PASID. Private io_mm has a NULL mm_struct pointer, and cannot be bound to
> multiple devices. The mm_alloc() IOMMU op must now check if the mm
> argument is NULL, in which case it should allocate io_pgtables instead of
> binding to an mm.
> 
> Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> ---
> Sadly this probably won't be the final thing. The API in this patch is
> used like this:
> 
>         iommu_sva_alloc_pasid(dev, &io_mm) -> PASID
>         iommu_sva_map(io_mm, ...)
>         iommu_sva_unmap(io_mm, ...)
>         iommu_sva_free_pasid(dev, io_mm)
> 
> The proposed API for auxiliary domains is in an early stage but might
> replace this patch and could be used like this:
> 
>         iommu_enable_aux_domain(dev)
>         d = iommu_domain_alloc()
>         iommu_attach_aux(dev, d)
>         iommu_aux_id(d) -> PASID
>         iommu_map(d, ...)
>         iommu_unmap(d, ...)
>         iommu_detach_aux(dev, d)
>         iommu_domain_free(d)
> 
> The advantage being that the driver doesn't have to use a special
> version of map/unmap/etc.

Hi Jean-Phillippe -

Have you thought about this any more? I want to send out a
refresh for the per-context pagetables for arm-smmu so if we want to change
the underlying assumptions this would be a great time.

For my part I'm okay with either model. In fact the second one is closer
to the original implementation that I sent out so I have a clear development
path in mind for either option depending on what the community decides.

Thanks,
Jordan

<snip the rest of the patch>

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