Re: [PATCH kernel v2 3/3] powerpc/iommu: Add iommu_ops to report capabilities and allow blocking domains

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Sep 20, 2022 at 11:04:57PM +1000, Alexey Kardashevskiy wrote:
> Up until now PPC64 managed to avoid using iommu_ops. The VFIO driver
> uses a SPAPR TCE sub-driver and all iommu_ops uses were kept in
> the Type1 VFIO driver. Recent development added 2 uses of iommu_ops to
> the generic VFIO which broke POWER:
> - a coherency capability check;
> - blocking IOMMU domain - iommu_group_dma_owner_claimed()/...
> 
> This adds a simple iommu_ops which reports support for cache
> coherency and provides a basic support for blocking domains. No other
> domain types are implemented so the default domain is NULL.
> 
> Since now iommu_ops controls the group ownership, this takes it out of
> VFIO.
> 
> This adds an IOMMU device into a pci_controller (=PHB) and registers it
> in the IOMMU subsystem, iommu_ops is registered at this point.
> This setup is done in postcore_initcall_sync.
> 
> This replaces iommu_group_add_device() with iommu_probe_device() as
> the former misses necessary steps in connecting PCI devices to IOMMU
> devices. This adds a comment about why explicit iommu_probe_device()
> is still needed.
> 
> Fixes: e8ae0e140c05 ("vfio: Require that devices support DMA cache coherence")
> Fixes: 70693f470848 ("vfio: Set DMA ownership for VFIO devices")
> Cc: Deming Wang <wangdeming@inspur.com>
> Cc: Robin Murphy <robin.murphy@arm.com>
> Cc: Jason Gunthorpe <jgg@nvidia.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>
> Cc: Daniel Henrique Barboza <danielhb413@gmail.com>
> Cc: Fabiano Rosas <farosas@linux.ibm.com>
> Cc: Murilo Opsfelder Araujo <muriloo@linux.ibm.com>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> Changes:
> v2:
> * replaced a default domain with blocked

Code wise this is much better..

But it is a bit unsettling to see the blocked domain co-opted to mean
'some platform specific VFIO behavior' - don't have a better idea for
this series though.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason