Merge branch 'vsock-virtio'

Stefan Hajnoczi says:

====================
Add virtio transport for AF_VSOCK

v2:
 * Rebased onto Linux v4.4-rc2
 * vhost: Refuse to assign reserved CIDs
 * vhost: Refuse guest CID if already in use
 * vhost: Only accept correctly addressed packets (no spoofing!)
 * vhost: Support flexible rx/tx descriptor layout
 * vhost: Add missing total_tx_buf decrement
 * virtio_transport: Fix total_tx_buf accounting
 * virtio_transport: Add virtio_transport global mutex to prevent races
 * common: Notify other side of SOCK_STREAM disconnect (fixes shutdown
   semantics)
 * common: Avoid recursive mutex_lock(tx_lock) for write_space (fixes deadlock)
 * common: Define VIRTIO_VSOCK_TYPE_STREAM/DGRAM hardware interface constants
 * common: Define VIRTIO_VSOCK_SHUTDOWN_RCV/SEND hardware interface constants
 * common: Fix peer_buf_alloc inheritance on child socket

This patch series adds a virtio transport for AF_VSOCK (net/vmw_vsock/).
AF_VSOCK is designed for communication between virtual machines and
hypervisors.  It is currently only implemented for VMware's VMCI transport.

This series implements the proposed virtio-vsock device specification from
here:
http://comments.gmane.org/gmane.comp.emulators.virtio.devel/855

Most of the work was done by Asias He and Gerd Hoffmann a while back.  I have
picked up the series again.

The QEMU userspace changes are here:
https://github.com/stefanha/qemu/commits/vsock

Why virtio-vsock?
-----------------
Guest<->host communication is currently done over the virtio-serial device.
This makes it hard to port sockets API-based applications and is limited to
static ports.

virtio-vsock uses the sockets API so that applications can rely on familiar
SOCK_STREAM and SOCK_DGRAM semantics.  Applications on the host can easily
connect to guest agents because the sockets API allows multiple connections to
a listen socket (unlike virtio-serial).  This simplifies the guest<->host
communication and eliminates the need for extra processes on the host to
arbitrate virtio-serial ports.

Overview
--------
This series adds 3 pieces:

1. virtio_transport_common.ko - core virtio vsock code that uses vsock.ko

2. virtio_transport.ko - guest driver

3. drivers/vhost/vsock.ko - host driver

Howto
-----
The following kernel options are needed:
  CONFIG_VSOCKETS=y
  CONFIG_VIRTIO_VSOCKETS=y
  CONFIG_VIRTIO_VSOCKETS_COMMON=y
  CONFIG_VHOST_VSOCK=m

Launch QEMU as follows:
  # qemu ... -device vhost-vsock-pci,id=vhost-vsock-pci0,guest-cid=3

Guest and host can communicate via AF_VSOCK sockets.  The host's CID (address)
is 2 and the guest is automatically assigned a CID (use VMADDR_CID_ANY (-1) to
bind to it).

Status
------
There are a few design changes I'd like to make to the virtio-vsock device:

1. The 3-way handshake isn't necessary over a reliable transport (virtqueue).
   Spoofing packets is also impossible so the security aspects of the 3-way
   handshake (including syn cookie) add nothing.  The next version will have a
   single operation to establish a connection.

2. Credit-based flow control doesn't work for SOCK_DGRAM since multiple clients
   can transmit to the same listen socket.  There is no way for the clients to
   coordinate buffer space with each other fairly.  The next version will drop
   credit-based flow control for SOCK_DGRAM and only rely on best-effort
   delivery.  SOCK_STREAM still has guaranteed delivery.

3. In the next version only the host will be able to establish connections
   (i.e. to connect to a guest agent).  This is for security reasons since
   there is currently no ability to provide host services only to certain
   guests.  This also matches how AF_VSOCK works on modern VMware hypervisors.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

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