Hypervisor

[a] The term dates to circa 1970;[3] IBM coined it for software that ran OS/360 and the 7090 emulator concurrently on the 360/65[4] and later used it for the DIAG handler of CP-67.

Specifically in these contexts, a hypervisor is a microkernel implementing virtualization infrastructure that must run in kernel-space for technical reasons, such as Intel VMX.

CP-40 ran on a S/360-40 modified at the Cambridge Scientific Center to support dynamic address translation, a feature that enabled virtualization.

Prior to this time, computer hardware had only been virtualized to the extent to allow multiple user applications to run concurrently, such as in CTSS and IBM M44/44X.

Both VM and CP/CMS enjoyed early acceptance and rapid development by universities, corporate users, and time-sharing vendors, as well as within IBM.

Users played an active role in ongoing development, anticipating trends seen in modern open source projects.

As mentioned above, the VM control program includes a hypervisor-call handler that intercepts DIAG ("Diagnose", opcode x'83') instructions used within a virtual machine.

This provides fast-path non-virtualized execution of file-system access and other operations (DIAG is a model-dependent privileged instruction, not used in normal programming, and thus is not virtualized.

Although Solaris has always been the only guest domain OS officially supported by Sun/Oracle on their Logical Domains hypervisor, as of late 2006[update], Linux (Ubuntu and Gentoo), and FreeBSD have been ported to run on top of the hypervisor (and can all run simultaneously on the same processor, as fully virtualized independent guest OSes).

Itanium can run HP-UX, Linux, Windows and OpenVMS, and these environments are also supported as virtual servers on HP's Integrity VM platform.

The HP-UX operating system hosts the Integrity VM hypervisor layer that allows for many important features of HP-UX to be taken advantage of and provides major differentiation between this platform and other commodity platforms - such as processor hotswap, memory hotswap, and dynamic kernel updates without system reboot.

While it heavily leverages HP-UX, the Integrity VM hypervisor is really a hybrid that runs on bare-metal while guests are executing.

because Integrity VM implements its own memory management, scheduling and I/O policies that are tuned for virtual machines and are not as effective for normal applications.

Similar trends have occurred with x86/x86-64 server platforms, where open-source projects such as Xen have led virtualization efforts.

This still leaves x86, MIPS, ARM and PowerPC as widely deployed architectures on medium- to high-end embedded systems.

Implementation of the concept has allegedly occurred in the SubVirt laboratory rootkit (developed jointly by Microsoft and University of Michigan researchers[18]) as well as in the Blue Pill malware package.

[19] In 2009, researchers from Microsoft and North Carolina State University demonstrated a hypervisor-layer anti-rootkit called Hooksafe that can provide generic protection against kernel-mode rootkits.