linux-kernel - RE: [PATCH v7 3/4] iommu/vt-d: Add set_dev

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Message-ID: <BN9PR11MB5276FC89BD8364776498B8AD8C5AA@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Wed, 14 Jun 2023 08:13:49 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "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>
Subject: RE: [PATCH v7 3/4] iommu/vt-d: Add set_dev_pasid callback for dma
 domain

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Wednesday, May 31, 2023 1:09 AM
> 
> 
> >  *   2) all SVA domains share a reserved domain id per recommendation
> >  *      from VT-d spec (section 6.2.3.1) so domain_detach_iommu() is
> >  *      not required;
> 
> The DID should be managed and allocated for the S2 pointer and the
> flushing logic should work genericly by tracking the S2's being used
> and flushing their DIDs when all the S2s fall out of use. The special
> identity S2 just gets a static DID that never falls out of use.
> 

I'm not sure it's worthwhile to fake a identity S2 for the bare metal
SVA case. It's far simpler to special case the reserved DID value in
the SVM path.