Re: [PATCH v7 03/10] iommu/sva: Add iommu_sva_domain support

[Baolu Lu]

On 2022/5/25 08:44, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@xxxxxxxxxx>
> > 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@xxxxxxxxxxxxxxx>
> > > > 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@xxxxxxxxxxxxxxx/
>
> --
> > 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.

Yes. Learning from above discussion, we are about to implement the
set_dev_pasid and blocking domain in parallel. We will convert all
the callback names to set_dev and set_dev_pasid after blocking domain
support is merged.

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

Yes. I have already started to implement the blocking domain in Intel
driver. With it as an example, we can extend it to other possible IOMMU
drivers.

Best regards,
baolu