Glossary #

A software program available in YaST and Virtual Machine Manager that provides a graphical interface to guide you through the steps to create virtual machines. It can also be run in text mode by entering virt-install at a command prompt in the host environment.

The term is used in Xen environments, and refers to a virtual machine. The host operating system is actually a virtual machine running in a privileged domain and can be called Dom0. All other virtual machines on the host run in unprivileged domains and can be called domain U's.

Intel* and AMD* provide virtualization hardware-assisted technology. This reduces the frequency of VM IN/OUT (fewer VM traps), because software is a major source of overhead, and increases the efficiency (the execution is done by the hardware). Moreover, this reduces the memory footprint, provides better resource control, and allows secure assignment of specific I/O devices.

The desktop or command line environment that allows interaction with the host computer's environment. It provides a command line environment and can also include a graphical desktop, such as GNOME or IceWM. The host environment runs as a special type of virtual machine that has privileges to control and manage other virtual machines. Other commonly used terms include Dom0, privileged domain, and host operating system.

The software that coordinates the low-level interaction between virtual machines and the underlying physical computer hardware.

See Chapter 3, Introduction to KVM Virtualization

The video output device that drives a video display from a memory buffer containing a complete frame of data for virtual machine displays running in paravirtual mode.

Virtualization Host Server

The physical computer running a SUSE virtualization platform software. The virtualization environment consists of the hypervisor, the host environment, virtual machines, and associated tools, commands, and configuration files. Other commonly used terms include host, Host Computer, Host Machine (HM), Virtual Server (VS), Virtual Machine Host (VMH), and VM Host Server (VHS).

VirtFS is a new paravirtualized file system interface designed for improving pass-through technologies in the KVM environment. It is based on the VirtIO framework.

A virtualized PC environment (VM) capable of hosting a guest operating system and associated applications. Could be also called a VM Guest.

A software program that provides a graphical user interface for creating and managing virtual machines.

A guest operating system or application running on a virtual machine.

See Chapter 2, Introduction to Xen Virtualization

A set of commands for Xen that lets administrators manage virtual machines from a command prompt on the host computer. It replaced the deprecated xm tool stack.

Virtual CPU capping allows you to set vCPU capacity to 1–100 percent of the physical CPU capacity.

CPU hotplugging is used to describe the functions of replacing/adding/removing a CPU without shutting down the system.

Virtual CPU over-commitment is the ability to assign more virtual CPUs to VMs than the actual number of physical CPUs present in the physical system. This procedure does not increase the overall performance of the system, but might be useful for testing purposes.

Processor affinity, or CPU pinning enables the binding and unbinding of a process or a thread to a central processing unit (CPU) or a range of CPUs.

A type of network connection that lets a virtual machine be identified on an external network as a unique identity that is separate from and unrelated to its host computer.

A type of network bridge that has no physical network device or virtual network device provided by the host. This lets virtual machines communicate with other virtual machines on the same host but not with the host or on an external network.

The network outside a host's internal network environment.

A type of network configuration that restricts virtual machines to their host environment.

A type of network bridge that has a virtual network device but no physical network device provided by the host. This lets virtual machines communicate with the host and other virtual machines on the host. Virtual machines can communicate on an external network through the host.

A type of network connection that lets a virtual machine use the IP address and MAC address of the host.

A type of network bridge that has a physical network device but no virtual network device provided by the host. This lets virtual machines communicate on an external network but not with the host. This lets you separate virtual machine network communications from the host environment.

A type of network bridge that has both a physical network device and a virtual network device provided by the host.

The Advanced Host Controller Interface (AHCI) is a technical standard defined by Intel* that specifies the operation of Serial ATA (SATA) host bus adapters in a non-implementation-specific manner.

Data storage devices, such as CD-ROM drives or disk drives, that move data in the form of blocks. Partitions and volumes are also considered block devices.

A virtual disk based on a file, also called a disk image file.

A method of accessing data on a disk at the individual byte level instead of through its file system.

A disk image file that does not reserve its entire amount of disk space but expands as data is written to it.

The drive designation given to the first virtual disk on a paravirtual machine.

Kernel Control Groups (commonly called “cgroups”) are a kernel feature that allows aggregating or partitioning tasks (processes) and all their children into hierarchical organized groups to isolate resources.

See also Chapter 9, Kernel Control Groups.

A change root (chroot, or change root jail) is a section in the file system that is isolated from the rest of the file system. For this purpose, the chroot or pivot_root command is used to change the root of the file system. A program that is executed in such a “chroot jail” cannot access files outside the designated directory tree.

Can be seen as a kind of “virtual machine” on the host server that can run any Linux system, for example openSUSE, SUSE Linux Enterprise Desktop, or SUSE Linux Enterprise Server. The main difference with a normal virtual machine is that the container shares its kernel with the host it runs on.

A kernel feature to isolate some resources like network, users, and others for a group of processes.

Advanced Configuration and Power Interface (ACPI) specification provides an open standard for device configuration and power management by the operating system.

Advanced Error Reporting

AER is a capability provided by the PCI Express specification which allows for reporting of PCI errors and recovery from some of them.

Advanced Programmable Interrupt Controller (APIC) is a family of interrupt controllers.

Bus:Device:Function

Notation used to succinctly describe PCI and PCIe devices.

Control Groups

Feature to limit, account and isolate resource usage (CPU, memory, disk I/O, etc.).

Earliest Deadline First

This scheduler provides weighted CPU sharing in an intuitive way and uses real-time algorithms to ensure time guarantees.

Extended Page Tables

Performance in a virtualized environment is close to that in a native environment. Virtualization does create some overheads, however. These come from the virtualization of the CPU, the MMU, and the I/O devices. In some recent x86 processors AMD and Intel have begun to provide hardware extensions to help bridge this performance gap. In 2006, both vendors introduced their first generation hardware support for x86 virtualization with AMD-Virtualization (AMD-V) and Intel® VT-x technologies. Recently Intel introduced its second generation of hardware support that incorporates MMU-virtualization, called Extended Page Tables (EPT). EPT-enabled systems can improve performance compared to using shadow paging for MMU virtualization. EPT increases memory access latencies for a few workloads. This cost can be reduced by effectively using large pages in the guest and the hypervisor.

Flux Advanced Security Kernel

Xen implements a type of mandatory access control via a security architecture called FLASK using a module of the same name.

High Assurance Platform

HAP combines hardware and software technologies to improve workstation and network security.

Hardware Virtual Machine (commonly called like this by Xen).

Input/Output Memory Management Unit

IOMMU (AMD* technology) is a memory management unit (MMU) that connects a direct memory access-capable (DMA-capable) I/O bus to the main memory.

Kernel Same Page Merging

KSM allows for automatic sharing of identical memory pages between guests to save host memory. KVM is optimized to use KSM if enabled on the VM Host Server.

Memory Management Unit

is a computer hardware component responsible for handling accesses to memory requested by the CPU. Its functions include translation of virtual addresses to physical addresses (that is, virtual memory management), memory protection, cache control, bus arbitration and in simpler computer architectures (especially 8-bit systems) bank switching.

Physical Address Extension

32-bit x86 operating systems use Physical Address Extension (PAE) mode to enable addressing of more than 4 GB of physical memory. In PAE mode, page table entries (PTEs) are 64 bits in size.

Process-context identifiers

These are a facility by which a logical processor may cache information for multiple linear-address spaces so that the processor may retain cached information when software switches to a different linear address space. INVPCID instruction is used for fine-grained TLB flush, which is benefit for kernel.

Peripheral Component Interconnect Express

PCIe was designed to replace older PCI, PCI-X and AGP bus standards. PCIe has numerous improvements including a higher maximum system bus throughput, a lower I/O pin count and smaller physical footprint. Moreover it also has a more detailed error detection and reporting mechanism (AER), and a native hotplug functionality. It is also backward compatible with PCI.

Page Size Extended

PSE refers to a feature of x86 processors that allows for pages larger than the traditional 4 KiB size. PSE-36 capability offers 4 more bits, in addition to the normal 10 bits, which are used inside a page directory entry pointing to a large page. This allows a large page to be located in 36-bit address space.

Page Table

A page table is the data structure used by a virtual memory system in a computer operating system to store the mapping between virtual addresses and physical addresses. Virtual addresses are those unique to the accessing process. Physical addresses are those unique to the hardware (RAM).

QXL is a cirrus VGA framebuffer (8M) driver for virtualized environment.

Rapid Virtualization Indexing, Nested Page Tables

An AMD second generation hardware-assisted virtualization technology for the processor memory management unit (MMU).

Serial ATA

SATA is a computer bus interface that connects host bus adapters to mass storage devices such as hard disks and optical drives.

Sandboxed environment where only predetermined system calls are permitted for added protection against malicious behavior.

Supervisor Mode Execution Protection

This prevents the execution of user-mode pages by the Xen hypervisor, making many application-to-hypervisor exploits much harder.

Simple Protocol for Independent Computing Environments

An SXP file is a Xen Configuration File.

Tiny Code Generator

Instructions are emulated rather than executed by the CPU.

Transparent Huge Pages

This allows CPUs to address memory using pages larger than the default 4 KB. This helps reduce memory consumption and CPU cache usage. KVM is optimized to use THP (via madvise and opportunistic methods) if enabled on the VM Host Server.

Translation Lookaside Buffer

TLB is a cache that memory management hardware uses to improve virtual address translation speed. All current desktop, notebook, and server processors use a TLB to map virtual and physical address spaces, and it is nearly always present in any hardware that uses virtual memory.

A scheduling entity, containing each state for virtualized CPU.

Virtual Desktop Infrastructure

Since kernel v3.6; a new method of accessing PCI devices from user space called VFIO.

Virtualization Host Server

VMM will run in VMX root operation and guest software will run in VMX non-root operation. Transitions between VMX root operation and VMX non-root operation are called VMX transitions.

Virtual Machine Control Structure

VMX non-root operation and VMX transitions are controlled by a data structure called a virtual-machine control structure (VMCS). Access to the VMCS is managed through a component of processor state called the VMCS pointer (one per logical processor). The value of the VMCS pointer is the 64-bit address of the VMCS. The VMCS pointer is read and written using the instructions VMPTRST and VMPTRLD. The VMM configures a VMCS using the VMREAD, VMWRITE, and VMCLEAR instructions. A VMM could use a different VMCS for each virtual machine that it supports. For a virtual machine with multiple logical processors (virtual processors), the VMM could use a different VMCS for each virtual processor.

Virtual Machine Device Queue

Multi-queue network adapters exist which support multiple VMs at the hardware level, having separate packet queues associated to the different hosted VMs (by means of the IP addresses of the VMs).

Virtual Machine Monitor (Hypervisor)

When the processor encounters an instruction or event of interest to the Hypervisor (VMM), it exits from guest mode back to the VMM. The VMM emulates the instruction or other event, at a fraction of native speed, and then returns to guest mode. The transitions from guest mode to the VMM and back again are high-latency operations, during which guest execution is completely stalled.

Virtual Machine eXtensions

New support for software control of TLB (VPID improves TLB performance with small VMM development effort).

Virtualization Technology for Directed I/O

Like IOMMU for Intel*.

Component to establish end-to-end integrity for guests via Trusted Computing.