Re: [RFC] /dev/ioasid uAPI proposal

Jason Gunthorpe
2021-06-03T12:49:29Z

On Thu, Jun 03, 2021 at 07:17:23AM +0000, Tian, Kevin wrote:
> > From: David Gibson <david@gibson.dropbear.id.au>
> > Sent: Wednesday, June 2, 2021 2:15 PM
> >
> [...]
> > > An I/O address space takes effect in the IOMMU only after it is attached
> > > to a device. The device in the /dev/ioasid context always refers to a
> > > physical one or 'pdev' (PF or VF).
> >
> > What you mean by "physical" device here isn't really clear - VFs
> > aren't really physical devices, and the PF/VF terminology also doesn't
> > extent to non-PCI devices (which I think we want to consider for the
> > API, even if we're not implemenenting it any time soon).
>
> Yes, it's not very clear, and more in PCI context to simplify the
> description. A "physical" one here means an PCI endpoint function
> which has a unique RID. It's more to differentiate with later mdev/
> subdevice which uses both RID+PASID. Naming is always a hard
> exercise to me... Possibly I'll just use device vs. subdevice in future
> versions.

Using PCI words:

A "physical" device is RID matching.

A "subdevice" is (RID, PASID) matching.

A "SW mdev" is performing DMA isolation in a device specific way - all
DMA's from the device are routed to the hypervisor's IOMMU page
tables.

Jason