linux-kernel - RE: [PATCH v7 03/10] iommu/sva: Add iommu_sva

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Date:   Wed, 25 May 2022 00:44:28 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        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>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jean-Philippe Brucker <jean-philippe@...aro.org>
Subject: RE: [PATCH v7 03/10] iommu/sva: Add iommu_sva_domain support

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Tuesday, May 24, 2022 9:39 PM
> 
> On Tue, May 24, 2022 at 09:39:52AM +0000, Tian, Kevin wrote:
> > > From: Lu Baolu <baolu.lu@...ux.intel.com>
> > > Sent: Thursday, May 19, 2022 3:21 PM
> > >
> > > The iommu_sva_domain represents a hardware pagetable that the
> IOMMU
> > > hardware could use for SVA translation. This adds some infrastructure
> > > to support SVA domain in the iommu common layer. It includes:
> > >
> > > - Add a new struct iommu_sva_domain and new IOMMU_DOMAIN_SVA
> > > domain
> > >   type.
> > > - Add a new domain ops pointer in iommu_ops. The IOMMU drivers that
> > >   support SVA should provide the callbacks.
> > > - Add helpers to allocate and free an SVA domain.
> > > - Add helpers to set an SVA domain to a device and the reverse
> > >   operation.
> > >
> > > Some buses, like PCI, route packets without considering the PASID value.
> > > Thus a DMA target address with PASID might be treated as P2P if the
> > > address falls into the MMIO BAR of other devices in the group. To make
> > > things simple, the attach/detach interfaces only apply to devices
> > > belonging to the singleton groups, and the singleton is immutable in
> > > fabric i.e. not affected by hotplug.
> > >
> > > The iommu_set/block_device_pasid() can be used for other purposes,
> > > such as kernel DMA with pasid, mediation device, etc. Hence, it is put
> > > in the iommu.c.
> >
> > usually we have 'set/clear' pair or 'allow/block'. Having 'set' paired
> > with 'block' doesn't read very clearly.
> 
> I thought we agreed we'd use the blocking domain for this? Why did it
> go back to an op?
> 

Probably it's based on following discussion:

https://lore.kernel.org/all/c8492b29-bc27-ae12-d5c4-9fbbc797e310@linux.intel.com/

--
> FWIW from my point of view I'm happy with having a .detach_dev_pasid op
> meaning implicitly-blocked access for now. 

If this is the path then lets not call it attach/detach
please. 'set_dev_pasid' and 'set_dev_blocking_pasid' are clearer
names.
--

Looks Baolu chooses this path and plans to use the blocking domain
later.

Thanks
Kevin