linux-kernel - RE: [PATCH v9 10/11] iommu: Per-domain I/O page fault handling

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Message-ID: <BN9PR11MB527605AA0663E8BE592898FE8CB89@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Tue, 28 Jun 2022 10:02:00 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jean-Philippe Brucker <jean-philippe@...aro.org>
CC:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        "Robin Murphy" <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v9 10/11] iommu: Per-domain I/O page fault handling

> From: Jean-Philippe Brucker <jean-philippe@...aro.org>
> Sent: Tuesday, June 28, 2022 5:44 PM
> 
> On Tue, Jun 28, 2022 at 08:39:36AM +0000, Tian, Kevin wrote:
> > > From: Lu Baolu <baolu.lu@...ux.intel.com>
> > > Sent: Tuesday, June 21, 2022 10:44 PM
> > >
> > > Tweak the I/O page fault handling framework to route the page faults to
> > > the domain and call the page fault handler retrieved from the domain.
> > > This makes the I/O page fault handling framework possible to serve more
> > > usage scenarios as long as they have an IOMMU domain and install a
> page
> > > fault handler in it. Some unused functions are also removed to avoid
> > > dead code.
> > >
> > > The iommu_get_domain_for_dev_pasid() which retrieves attached
> domain
> > > for a {device, PASID} pair is used. It will be used by the page fault
> > > handling framework which knows {device, PASID} reported from the
> iommu
> > > driver. We have a guarantee that the SVA domain doesn't go away during
> > > IOPF handling, because unbind() waits for pending faults with
> > > iopf_queue_flush_dev() before freeing the domain. Hence, there's no
> need
> > > to synchronize life cycle of the iommu domains between the unbind() and
> > > the interrupt threads.
> >
> > I found iopf_queue_flush_dev() is only called in intel-iommu driver. Did
> > I overlook anything?
> 
> The SMMU driver will need it as well when we upstream PRI support.
> Currently it only supports stall, and that requires the device driver to
> flush all DMA including stalled transactions *before* calling unbind(), so
> ne need for iopf_queue_flush_dev() in this case.
>

then it makes sense. Probably Baolu can add this information in the
commit msg so others with similar question can quickly get the
point here.