I/O Sharing Approaches
Software-Based Sharing
The emulation layer interposes itself between the driver running in the guest OS and the underlying hardware. This level of indirection allows the VMM to intercept all traffic issued by the guest driver.
Emulation software can parse the I/O commands, translate guest addresses into host physical addresses, and ensure that all referenced memory pages are present in memory. Software must resolve the multiple I/O requests from all the virtual machines and serialize them into a single I/O stream that can be handled by the underlying hardware.
Common approaches to software-based sharing are
(1) device emulation and
(2) the splitdriver model
Direct Assignment
By directly exposing the hardware to the guest OS andrunning a native device driver, Intel has added enhancements to facilitate memory translation and ensure protection of memory that enables a device to directly DMA to/from host memory.
VMM utilizes and configures technologies such as Intel® VT-x and Intel® VT-d to perform address translation when sending data to and from an IO device
SR-IOV introduces two new function types:
• Physical Functions (PFs): These are full PCIe functions that include the SR-IOV Extended Capability. The capability is used to configure and manage the SR-IOV functionality.
• Virtual Functions (VFs): These are ‘lightweight’ PCIe functions that contain the resources necessary for data movement but have a carefully minimized set of configuration resources.
Important Issues in Windows Server 2012
https://technet.microsoft.com/en-us/library/jj134216.aspx
A BIOS update may be required for some computers to install the Hyper-V Role and/or start Hyper-V virtual machines
https://support.microsoft.com/en-us/kb/2762297
Intel® Virtualization Technology for Directed I/O (VT-d): Enhancing Intel platforms for efficient virtualization of I/O devices
https://software.intel.com/en-us/articles/intel-virtualization-technology-for-directed-io-vt-d-enhancing-intel-platforms-for-efficient-virtualization-of-io-devices/
SR-IOV
http://pcisig.com/specifications/iov/ats