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

[Yi Liu]

On 2024/5/29 20:02, Baolu Lu wrote:
> 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.

will it be more clear to name iommu_user_domain_alloc() be
iommu_user_paging_domain_alloc() as it is mainly for paging 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?

cool. BTW. I know out-of-tree drivers are not counted in upstream review.
Just out of curious, is there a formal way to let such drivers know it is
no longer allowed to use iommu_domain_alloc() on VT-d?

--
Regards,
Yi Liu