Re: [PATCH V4 05/18] iommu/ioasid: Redefine IOASID set and allocation APIs

Jason Gunthorpe
2021-04-07T19:37:01Z

On Wed, Apr 07, 2021 at 08:43:50PM +0200, Jean-Philippe Brucker wrote:

> * Get a container handle out of /dev/ioasid (or /dev/iommu, really.)
> No operation available since we don't know what the device and IOMMU
> capabilities are.
>
> * Attach the handle to a VF. With VFIO that would be
> VFIO_GROUP_SET_CONTAINER. That causes the kernel to associate an IOMMU
> with the handle, and decide which operations are available.

Right, this is basically the point, - the VFIO container (/dev/vfio)
and the /dev/ioasid we are talking about have a core of
similarity. ioasid is the generalized, modernized, and cross-subsystem
version of the same idea. Instead of calling it "vfio container" we
call it something that evokes the idea of controlling the iommu.

The issue is to seperate /dev/vfio generic functionality from vfio and
share it with every subsystem.

It may be that /dev/vfio and /dev/ioasid end up sharing a lot of code,
with a different IOCTL interface around it. The vfio_iommu_driver_ops
is not particularly VFIOy.

Creating /dev/ioasid may primarily start as a code reorganization
exercise.

> * With a map/unmap vIOMMU (or shadow mappings), a single translation level
> is supported. With a nesting vIOMMU, we're populating the level-2
> translation (some day maybe by binding the KVM page tables, but
> currently with map/unmap ioctl).
>
> Single-level translation needs single VF per container.

Really? Why?

Jason