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

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Date:   Tue, 31 May 2022 13:44:14 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>,
        "Tian, Kevin" <kevin.tian@...el.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>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v4 1/6] iommu: Add a per domain PASID for DMA API

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.

Thanks,

Jacob