An Intel MIC X100 device is a PCIe form factor add-in coprocessor
  card based on the Intel Many Integrated Core (MIC) architecture
  that runs a Linux OS. It is a PCIe endpoint in a platform and therefore
  implements the three required standard address spaces i.e. configuration,
  memory and I/O. The host OS loads a device driver as is typical for
  PCIe devices. The card itself runs a bootstrap after reset that

  transfers control to the card OS downloaded from the host driver. The
  host driver supports OSPM suspend and resume operations. It shuts down
  the card during suspend and reboots the card OS during resume.

  The card OS as shipped by Intel is a Linux kernel with modifications
  for the X100 devices.
  
  Since it is a PCIe card, it does not have the ability to host hardware
  devices for networking, storage and console. We provide these devices

  on X100 coprocessors thus enabling a self-bootable equivalent
  environment for applications. A key benefit of our solution is that it
  leverages the standard virtio framework for network, disk and console
  devices, though in our case the virtio framework is used across a PCIe
  bus. A Virtio Over PCIe (VOP) driver allows creating user space
  backends or devices on the host which are used to probe virtio drivers
  for these devices on the MIC card. The existing VRINGH infrastructure
  in the kernel is used to access virtio rings from the host. The card
  VOP driver allows card virtio drivers to communicate with their user
  space backends on the host via a device page. Ring 3 apps on the host
  can add, remove and configure virtio devices. A thin MIC specific
  virtio_config_ops is implemented which is borrowed heavily from
  previous similar implementations in lguest and s390.

  MIC PCIe card has a dma controller with 8 channels. These channels are
  shared between the host s/w and the card s/w. 0 to 3 are used by host
  and 4 to 7 by card. As the dma device doesn't show up as PCIe device,
  a virtual bus called mic bus is created and virtual dma devices are
  created on it by the host/card drivers. On host the channels are private
  and used only by the host driver to transfer data for the virtio devices.

  The Symmetric Communication Interface (SCIF (pronounced as skiff)) is a
  low level communications API across PCIe currently implemented for MIC.
  More details are available at scif_overview.txt.

  The Coprocessor State Management (COSM) driver on the host allows for
  boot, shutdown and reset of Intel MIC devices. It communicates with a COSM
  "client" driver on the MIC cards over SCIF to perform these functions.

  Here is a block diagram of the various components described above. The
  virtio backends are situated on the host rather than the card given better
  single threaded performance for the host compared to MIC, the ability of
  the host to initiate DMA's to/from the card using the MIC DMA engine and
  the fact that the virtio block storage backend can only be on the host.

                 +----------+           |             +----------+
                 | Card OS  |           |             | Host OS  |
                 +----------+           |             +----------+
                                        |
          +-------+ +--------+ +------+ | +---------+  +--------+ +--------+
          | Virtio| |Virtio  | |Virtio| | |Virtio   |  |Virtio  | |Virtio  |
          | Net   | |Console | |Block | | |Net      |  |Console | |Block   |
          | Driver| |Driver  | |Driver| | |backend  |  |backend | |backend |

          +---+---+ +---+----+ +--+---+ | +---------+  +----+---+ +--------+

              |         |         |     |      |            |         |
              |         |         |     |User  |            |         |

              |         |         |     |------|------------|--+------|-------
              +---------+---------+     |Kernel                |
                        |               |                      |
    +---------+     +---+----+ +------+ | +------+ +------+ +--+---+  +-------+
    |MIC DMA  |     |  VOP   | | SCIF | | | SCIF | | COSM | | VOP  |  |MIC DMA|
    +---+-----+     +---+----+ +--+---+ | +--+---+ +--+---+ +------+  +----+--+
        |               |         |     |    |        |                    |
    +---+-----+     +---+----+ +--+---+ | +--+---+ +--+---+ +------+  +----+--+
    |MIC      |     |  VOP   | |SCIF  | | |SCIF  | | COSM | | VOP  |  | MIC   |
    |HW Bus   |     |  HW Bus| |HW Bus| | |HW Bus| | Bus  | |HW Bus|  |HW Bus |
    +---------+     +--------+ +--+---+ | +--+---+ +------+ +------+  +-------+
        |               |         |     |       |     |                    |
        |   +-----------+--+      |     |       |    +---------------+     |
        |   |Intel MIC     |      |     |       |    |Intel MIC      |     |
        |   |Card Driver   |      |     |       |    |Host Driver    |     |
        +---+--------------+------+     |       +----+---------------+-----+

                   |                    |                   |

               +-------------------------------------------------------------+
               |                                                             |
               |                    PCIe Bus                                 |
               +-------------------------------------------------------------+