RE: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API

[Tian, Kevin]

> From: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Sent: Wednesday, June 1, 2022 4:44 AM
> 
> Hi Jason,
> 
> On Tue, 31 May 2022 16:05:50 -0300, Jason Gunthorpe <jgg@xxxxxxxxxx>
> wrote:
> 
> > On Tue, May 31, 2022 at 10:29:55AM -0700, Jacob Pan wrote:
> >
> > > The reason why I store PASID at IOMMU domain is for IOTLB flush within
> > > the domain. Device driver is not aware of domain level IOTLB flush. We
> > > also have iova_cookie for each domain which essentially is for
> > > RIDPASID.
> >
> > You need to make the PASID stuff work generically.
> >
> > The domain needs to hold a list of all the places it needs to flush
> > and that list needs to be maintained during attach/detach.
> >
> > A single PASID on the domain is obviously never going to work
> > generically.
> >
> I agree, I did it this way really meant to be part of iommu_domain's
> iommu_dma_cookie, not meant to be global. But for the lack of common
> storage between identity domain and dma domain, I put it here as global.
> 
> Then should we also extract RIDPASID to become part of the generic API?
> i.e. set pasid, flush IOTLB etc. Right? RIDPASID is not in group's
> pasid_array today.
> 

RIDPASID is just an alias to RID in the PASID table (similar to pasid#0
on other platforms). it's reserved and not exposed outside the 
intel-iommu driver. So I don't think it should be managed via the
generic iommu API. But probably you can generalize it with other
pasids within intel-iommu driver if doing so can simplify the logic
there.