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

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Message-ID: <20220316140140.76bb24c6@jacob-builder>
Date:   Wed, 16 Mar 2022 14:01:40 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        "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>, jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v2 3/8] iommu/vt-d: Implement device_pasid domain attach
 ops

Hi Kevin,

On Wed, 16 Mar 2022 07:41:34 +0000, "Tian, Kevin" <kevin.tian@...el.com>
wrote:

> > 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.  
> 
Perhaps i mis-presented here, I am not using 2D array. It is an 1D xarray
for domain PASIDs only. Then I use the existing device list in each domain,
adding another xa to track per-device-domain PASIDs.
> 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.
> 
Sorry, could you elaborate? If we do per-dev PASID allocation, we could use
the ioasid_set for each pdev, right?

> > 
> > 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. 😊
> 
I commented on the other email, but a simple list of tuples could have
duplicated devices since each dev could attach multiple PASIDs, right?
Should we still do two level then?

> Thanks
> Kevin


Thanks,

Jacob