Re: Plan for /dev/ioasid RFC v2

[Jason Gunthorpe]

On Mon, Jun 28, 2021 at 06:45:23AM +0000, Tian, Kevin wrote:

> 7)   Unbinding detaches the device from the block_dma domain and
>        re-attach it to the default domain. From now on the user should 
>        be denied from accessing the device. vfio should tear down the
>        MMIO mapping at this point.

I think we should just forbid this, so long as the device_fd is open
the iommu_fd cannot be destroyed and there is no way to detact a
device other than closing its Fd.

revoke is tricky enough to implement we should avoid it.

> It's still an open whether we want to further allow devices within a group 
> attached to different IOASIDs in case that the source devices are reliably 
> identifiable. This is an usage not supported by existing vfio and might be
> not worthwhile due to improved isolation over time.

The main decision here is to decide if the uAPI should have some way to
indicate that a device does not have its own unique IOASID but is
sharing with the group

Jason