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

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Message-ID: <20220315230457.GO11336@nvidia.com>
Date:   Tue, 15 Mar 2022 20:04:57 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     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>,
        Jacob Pan <jacob.jun.pan@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        "Zanussi, Tom" <tom.zanussi@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>, Yi Liu <yi.l.liu@...el.com>
Subject: Re: [PATCH v2 3/8] iommu/vt-d: Implement device_pasid domain attach
 ops

On Tue, Mar 15, 2022 at 03:36:20PM -0700, Jacob Pan wrote:
> Hi Jason,
> 
> On Tue, 15 Mar 2022 11:33:22 -0300, Jason Gunthorpe <jgg@...dia.com> wrote:
> 
> > 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.
> > 
> > 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..
> > 
> Agreed.
> It might need some surgery for dmar_domain and device_domain_info, which
> already has a simple device list. I am trying to leverage the existing data
> struct, let me take a closer look.

Maybe the core code should provide this data structure in the
iommu_domain.

Figuring out what stuff is attached is something every driver has to
do right?

Jason