[Xen Hackathon] new PV drivers

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

Present (by memory):
- Julien Grall,
- Stefano Stabellini,
- Ian Campbell,
- Roger Pau Monne,
- Dario Faggioli,
- Andrii Tseglytskyi,
- David Vrabel,
- Konrad Wilk.

* What new PV devices do we need? What has been done already?
* Where should they live?


New PV Drivers, GlobalLogic has done:
- PV tiny-ALSA, very simple forwarding, backend in Linux, frontend is
  userspace, stand-alone. Could be in their own git tree on xenbits.
- Made old PV USB patches working, backend and frontend in Linux.
- Improved PVFB: do they use the backend in QEMU? Can be upstreamed?
- PV WPA supplicant, WIP with simple frontend and backend in Linux.

IPU support (TI). We need Remote Proc Framework working on Xen:
http://lwn.net/Articles/489009/
We need PV Remote Proc to have HD video reproduction in Android.
We could use an IOMMU to assign the IPU to the domU but the IPU is not
behind an IOMMU.
We could use a PV protocol to assign the IPU to one domain, using Remove
Proc to talk to the other DomU.
The PV protocol would be a simple protocol to assign the IPU to one
domain only.
Dom0 could allocate the initial memory for IPU, we are sure it is
contiguous in machine memory because it is mapped 1:1.
Dom0 need to translate the addresses on behalf of the guest.
A limited IOMMU is present between IPU and main memory. Dom0 could
program it with the memory for the IPU.

GPU support. At the moment GlobalLogic is mapping memory and irqs into the
guest. Possibility of creating a frontend/backend protocol.
We could virtualize GPU similarly to the ALSA protocol: virtual EGL or
OpenGL ES.

David: new PV protocols need a standard state machine, we should
document what a basic PV protocol looks like.

IanC: what about the security implication of assigning GPU and IPU to
guests? Is that a problem?
Andrii: For now, it is acceptable.