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

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Date:   Wed, 1 Jun 2022 01:50:33 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Jean-Philippe Brucker" <jean-philippe@...aro.com>,
        Christoph Hellwig <hch@...radead.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "robin.murphy@....com" <robin.murphy@....com>,
        "will@...nel.org" <will@...nel.org>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        Eric Auger <eric.auger@...hat.com>
Subject: RE: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API

> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Sent: Wednesday, June 1, 2022 4:44 AM
> 
> Hi Jason,
> 
> On Tue, 31 May 2022 16:05:50 -0300, Jason Gunthorpe <jgg@...dia.com>
> 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.