Re: [PATCH kernel 1/3] powerpc/iommu: Add "borrowing" iommu_table_group_ops

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Jul 14, 2022 at 06:18:20PM +1000, Alexey Kardashevskiy wrote:
> PPC64 IOMMU API defines iommu_table_group_ops which handles DMA windows
> for PEs: control the ownership, create/set/unset a table the hardware
> for dynamic DMA windows (DDW). VFIO uses the API to implement support
> on POWER.
> 
> So far only PowerNV IODA2 (POWER8 and newer machines) implemented this and other cases (POWER7 or nested KVM) did not and instead reused
> existing iommu_table structs. This means 1) no DDW 2) ownership transfer
> is done directly in the VFIO SPAPR TCE driver.
> 
> Soon POWER is going to get its own iommu_ops and ownership control is
> going to move there. This implements spapr_tce_table_group_ops which
> borrows iommu_table tables. The upside is that VFIO needs to know less
> about POWER.
> 
> The new ops returns the existing table from create_table() and
> only checks if the same window is already set. This is only going to work
> if the default DMA window starts table_group.tce32_start and as big as
> pe->table_group.tce32_size (not the case for IODA2+ PowerNV).
> 
> This changes iommu_table_group_ops::take_ownership() to return an error
> if borrowing a table failed.
> 
> This should not cause any visible change in behavior for PowerNV.
> pSeries was not that well tested/supported anyway.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
>  arch/powerpc/include/asm/iommu.h          |  6 +-
>  arch/powerpc/kernel/iommu.c               | 98 ++++++++++++++++++++++-
>  arch/powerpc/platforms/powernv/pci-ioda.c |  6 +-
>  arch/powerpc/platforms/pseries/iommu.c    |  3 +
>  drivers/vfio/vfio_iommu_spapr_tce.c       | 94 ++++------------------
>  5 files changed, 121 insertions(+), 86 deletions(-)

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

Jason