linux-kernel - RE: [PATCH v2 3/8] iommu/vt-d: Implement device

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Date:   Wed, 16 Mar 2022 07:41:34 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
CC:     "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>
Subject: RE: [PATCH v2 3/8] iommu/vt-d: Implement device_pasid domain attach
 ops

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Tuesday, March 15, 2022 10:33 PM
> 
> On Mon, Mar 14, 2022 at 10:07:07PM -0700, Jacob Pan wrote:
> > +	/*
> > +	 * Each domain could have multiple devices attached with shared or
> per
> > +	 * device PASIDs. At the domain level, we keep track of unique PASIDs
> and
> > +	 * device user count.
> > +	 * E.g. If a domain has two devices attached, device A has PASID 0, 1;
> > +	 * device B has PASID 0, 2. Then the domain would have PASID 0, 1, 2.
> > +	 */
> 
> A 2d array of xarray's seems like a poor data structure for this task.

besides that it also doesn't work when we support per-device PASID allocation
in the future. In that case merging device PASIDs together is conceptually
wrong.

> 
> AFACIT this wants to store a list of (device, pasid) tuples, so a
> simple linked list, 1d xarray vector or a red black tree seems more
> appropriate..
> 

this tuple can well serve per-device PASID. 😊

Thanks
Kevin