Re: [PATCH 3/6] vfio: remove the unused mdev iommu hook

Jason Gunthorpe
2021-05-13T12:01:05Z

On Thu, May 13, 2021 at 03:28:52AM +0000, Tian, Kevin wrote:

> Are you specially concerned about this iommu_device hack which
> directly connects mdev_device to iommu layer or the entire removed
> logic including the aux domain concept? For the former we are now
> following up the referred thread to find a clean way. But for the latter
> we feel it's still necessary regardless of how iommu interface is redesigned
> to support device connection from the upper level driver. The reason is
> that with mdev or subdevice one physical device could be attached to
> multiple domains now. there could be a primary domain with DOMAIN_
> DMA type for DMA_API use by parent driver itself, and multiple auxiliary
> domains with DOMAIN_UNMANAGED types for subdevices assigned to
> different VMs.

Why do we need more domains than just the physical domain for the
parent? How does auxdomain appear in /dev/ioasid?

I never understood what this dead code was supposed to be used for.

Jason