3.3.3. Physical Host Devices

The KVM hypervisor supports attaching PCI devices on the host system to virtual machines. PCI device assignment provides guests with exclusive access to PCI devices for a range of tasks. It enables PCI devices to appear and behave as if they were physically attached to the guest virtual machine.

Device assignment is supported on PCI Express devices, with the exception of graphics cards. Parallel PCI devices may be supported as assigned devices, but they have severe limitations due to security and system configuration conflicts.

The KVM hypervisor supports attaching USB devices on the host system to virtual machines. USB device assignment makes it possible for guests to have exclusive access to USB devices for a range of tasks. It also enables USB devices to appear and behave as if they were physically attached to the virtual machine.

SR-IOV (Single Root I/O Virtualization) is a PCI Express standard that extends a single physical PCI function to share its PCI resources as separate, virtual functions (VFs). Each function is capable of being used by a different virtual machine through PCI device assignment.

An SR-IOV-capable PCI-e device, provides a Single Root Function (for example, a single Ethernet port) and presents multiple, separate virtual devices as unique PCI device functions. Each virtual device may have its own unique PCI configuration space, memory-mapped registers, and individual MSI-based interrupts.

N_Port ID Virtualization (NPIV) is a functionality available with some Fibre Channel devices. NPIV shares a single physical N_Port as multiple N_Port IDs. NPIV provides similar functionality for Fibre Channel Host Bus Adapters (HBAs) that SR-IOV provides for PCIe interfaces. With NPIV, virtual machines can be provided with a virtual Fibre Channel initiator to Storage Area Networks (SANs).

NPIV can provide high density virtualized environments with enterprise-level storage solutions.