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

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Date:   Fri, 28 Apr 2023 08:56:15 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        Will Deacon <will@...nel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Yu, Fenghua" <fenghua.yu@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        "Ranganathan, Narayan" <narayan.ranganathan@...el.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v5 1/7] iommu: Generalize default PCIe requester ID
 PASID

Hi Kevin,

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

> > From: Jacob Pan <jacob.jun.pan@...ux.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