Re: [PATCH v5 1/7] iommu: Generalize default PCIe requester ID PASID

Jacob Pan
2023-04-28T15:52:02Z

Hi Kevin,

On Fri, 28 Apr 2023 09:38:32 +0000, "Tian, Kevin" <kevin.tian@intel.com>
wrote:

> > From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> > Sent: Friday, April 28, 2023 1:50 AM
> >
> > 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.
>
> You intend it to be generic but in the end only vt-d driver is changed
> to use it in this series...
change for SVA is in the patch.

> > @@ -190,6 +190,7 @@ enum iommu_dev_features {
> > IOMMU_DEV_FEAT_IOPF,
> > };
> >
> > +#define IOMMU_DEF_RID_PASID (0U) /* Reserved for DMA w/o PASID
> > */
>
> Is RID a general team on other platform?
RID, aka requester id is a PCI term. so I this it is common though on SMMU
might be better called stream ID PASID?

> Would IOMMU_DEF_NO_PASID serve the purpose better?
not sure, it is still a PASID. For completeness, might be called
IOMMU_DEF_PASID_FOR_DMA_NO_PASID :)

other suggestions?

Thanks,

Jacob