Re: [PATCH 00/20] iommu: Refactoring domain allocation interface

[Baolu Lu]

On 2024/5/29 17:03, Yi Liu wrote:
> On 2024/5/29 13:32, Lu Baolu wrote:
> > The IOMMU subsystem has undergone some changes, including the removal
> > of iommu_ops from the bus structure. Consequently, the existing domain
> > allocation interface, which relies on a bus type argument, is no longer
> > relevant:
> >
> >      struct iommu_domain *iommu_domain_alloc(struct bus_type *bus)
> >
> > This series is designed to refactor the use of this interface. It
> > proposes two new interfaces to replace iommu_domain_alloc():
> >
> > - iommu_user_domain_alloc(): This interface is intended for allocating
> >    iommu domains managed by userspace for device passthrough scenarios,
> >    such as those used by iommufd, vfio, and vdpa. It clearly indicates
> >    that the domain is for user-managed device DMA.
>
> user paging domain? It looks to me user domain includes the nested domains
> as well.

Yes, nested domain is a user domain. The iommu driver should implement
iommu_ops->domain_alloc_user for nested domain allocation.

> >    If an IOMMU driver does not implement iommu_ops->domain_alloc_user,
> >    this interface will rollback to the generic paging domain allocation.
> >
> > - iommu_paging_domain_alloc(): This interface is for allocating iommu
> >    domains managed by kernel drivers for kernel DMA purposes. It takes a
> >    device pointer as a parameter, which better reflects the current
> >    design of the IOMMU subsystem.
> >
> > The majority of device drivers currently using iommu_domain_alloc() do
> > so to allocate a domain for a specific device and then attach that
> > domain to the device. These cases can be straightforwardly migrated to
> > the new interfaces.
> >
> > However, there are some drivers with more complex use cases that do
> > not fit neatly into this new scheme. For example:
> >
> > $ git grep "= iommu_domain_alloc"
> > arch/arm/mm/dma-mapping.c:      mapping->domain = 
> > iommu_domain_alloc(bus);
> > drivers/gpu/drm/rockchip/rockchip_drm_drv.c:    private->domain = 
> > iommu_domain_alloc(private->iommu_dev->bus);
> > drivers/gpu/drm/tegra/drm.c:            tegra->domain = 
> > iommu_domain_alloc(&platform_bus_type);
> > drivers/infiniband/hw/usnic/usnic_uiom.c:       pd->domain = domain = 
> > iommu_domain_alloc(dev->bus);
> >
> > This series leave those cases unchanged and keep iommu_domain_alloc()
> > for their usage. But new drivers should not use it anymore.
>
> does it mean there is still domains allocated via iommu_domain_alloc()
> on VT-d platform?

I think the drivers mentioned above do not run on x86 platforms, or do
they?

Best regards,
baolu