RE: [RFC 08/20] vfio/pci: Add VFIO_DEVICE_BIND_IOMMUFD

["Tian, Kevin" <kevin.tian@intel.com>]

> From: Jason Gunthorpe <jgg@nvidia.com>
> Sent: Wednesday, September 29, 2021 8:28 PM
> 
> On Wed, Sep 29, 2021 at 06:41:00AM +0000, Tian, Kevin wrote:
> > > From: David Gibson <david@gibson.dropbear.id.au>
> > > Sent: Wednesday, September 29, 2021 2:01 PM
> > >
> > > On Sun, Sep 19, 2021 at 02:38:36PM +0800, Liu Yi L wrote:
> > > > This patch adds VFIO_DEVICE_BIND_IOMMUFD for userspace to bind
> the
> > > vfio
> > > > device to an iommufd. No VFIO_DEVICE_UNBIND_IOMMUFD interface
> is
> > > provided
> > > > because it's implicitly done when the device fd is closed.
> > > >
> > > > In concept a vfio device can be bound to multiple iommufds, each
> hosting
> > > > a subset of I/O address spaces attached by this device.
> > >
> > > I really feel like this many<->many mapping between devices is going
> > > to be super-confusing, and therefore make it really hard to be
> > > confident we have all the rules right for proper isolation.
> >
> > Based on new discussion on group ownership part (patch06), I feel this
> > many<->many relationship will disappear. The context fd (either container
> > or iommufd) will uniquely mark the ownership on a physical device and
> > its group. With this design it's impractical to have one device bound
> > to multiple iommufds.
> 
> That should be a requirement! We have no way to prove that two
> iommufds are the same security domain, so devices/groups cannot be
> shared.
> 
> That is why the API I suggested takes in a struct file to ID the user
> security context. A group is accessible only from that single struct
> file and no more.
> 
> If the first series goes the way I outlined then I think David's
> concern about security is strongly solved as the IOMMU layer is
> directly managing it with a very clear responsiblity and semantic.
> 

Yes, this is also my understanding now.