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SubjectRe: [PATCH v6 1/4] iommu: Generalize default PCIe requester ID PASID
On Fri, May 19, 2023 at 01:32:20PM -0700, Jacob Pan wrote:
> PCIe Process address space ID (PASID) is used to tag DMA traffic, it
> provides finer grained isolation than requester ID (RID).
>
> For each RID, 0 is as a special PASID for the legacy DMA (without
> PASID), thus RID_PASID. This is universal across all architectures,
> therefore warranted to be declared in the common header.
> Noting that VT-d could support none-zero RID_PASID, but currently not
> used.
>
> By having a common RID_PASID, we can avoid conflicts between different
> use cases in the generic code. e.g. SVA and DMA API with PASIDs.
>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> ---
> v6:
> - let SMMU code use the common RID_PASID macro
> ---
> .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 2 +-
> drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 10 ++++----
> drivers/iommu/intel/iommu.c | 24 +++++++++----------
> drivers/iommu/intel/pasid.c | 2 +-
> drivers/iommu/intel/pasid.h | 1 -
> include/linux/iommu.h | 1 +
> 6 files changed, 20 insertions(+), 20 deletions(-)

I tend to agree with Jean-Philippe's remarks on the name

This is the "untagged" DMA for environments that have optional tags.

Otherwise:

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

Jason

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