linux-kernel - Re: [PATCH v2 2/8] iommu: Add attach/detach_dev

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Date:   Fri, 18 Mar 2022 10:50:03 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     "Tian, Kevin" <kevin.tian@...el.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>,
        Jacob Pan <jacob.jun.pan@...ux.intel.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>,
        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 2/8] iommu: Add attach/detach_dev_pasid domain ops

On Fri, Mar 18, 2022 at 08:01:04PM +0800, Lu Baolu wrote:
> On 2022/3/15 19:49, Tian, Kevin wrote:
> > > From: Jean-Philippe Brucker<jean-philippe@...aro.org>
> > > Sent: Tuesday, March 15, 2022 7:27 PM
> > > 
> > > On Mon, Mar 14, 2022 at 10:07:06PM -0700, Jacob Pan wrote:
> > > > From: Lu Baolu<baolu.lu@...ux.intel.com>
> > > > 
> > > > An IOMMU domain represents an address space which can be attached by
> > > > devices that perform DMA within a domain. However, for platforms with
> > > > PASID capability the domain attachment needs be handled at device+PASID
> > > > level. There can be multiple PASIDs within a device and multiple devices
> > > > attached to a given domain.
> > > > This patch introduces a new IOMMU op which support device, PASID, and
> > > > IOMMU domain attachment. The immediate use case is for PASID capable
> > > > devices to perform DMA under DMA APIs.
> > > > 
> > > > Signed-off-by: Lu Baolu<baolu.lu@...ux.intel.com>
> > > > Signed-off-by: Jacob Pan<jacob.jun.pan@...ux.intel.com>
> > > >   include/linux/iommu.h | 6 ++++++
> > > >   1 file changed, 6 insertions(+)
> > > > 
> > > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> > > > index 369f05c2a4e2..fde5b933dbe3 100644
> > > > +++ b/include/linux/iommu.h
> > > > @@ -227,6 +227,8 @@ struct iommu_iotlb_gather {
> > > >    * @aux_get_pasid: get the pasid given an aux-domain
> > > >    * @sva_bind: Bind process address space to device
> > > >    * @sva_unbind: Unbind process address space from device
> > > > + * @attach_dev_pasid: attach an iommu domain to a pasid of device
> > > > + * @detach_dev_pasid: detach an iommu domain from a pasid of device
> > > Isn't that operation "assign a PASID to a domain" instead?  In patch 5,
> > > the domain is already attached to the device, so set_domain_pasid() might
> > > be clearer and to the point. If the IOMMU driver did the allocation we
> > > could also avoid patch 1.
> > iiuc this API can also work for future SIOV usage where each mdev attached
> > to the domain has its own pasid. "assigning a PASID to a domain" sounds
> > like going back to the previous aux domain approach which has one PASID
> > per domain and that PASID is used on all devices attached to the aux domain...
> > 
> 
> This also works for SVA as far as I can see. The sva_bind essentially is
> to  attach an SVA domain to the PASID of a device. The sva_bind/unbind
> ops could be removed with these two new callbacks.

As we talked before I would like to see 'sva bind' go away and be
replaced with:

  domain = alloc_sva_iommu_domain(device, current)
  attach_dev_pasid_domain(domain, device, pasid)

Which composes better with everything else. SVA is just a special kind
of iommu_domain

Jason