Electrical computers and digital processing systems: virtual mac – Virtual machine task or process management
Reexamination Certificate
2000-08-24
2004-08-31
An, Meng-Al T. (Department: 2127)
Electrical computers and digital processing systems: virtual mac
Virtual machine task or process management
C711S006000, C711S202000, C711S203000, C711S206000, C711S208000
Reexamination Certificate
active
06785886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a computer virtualization system and a related method of operation, in particular in the context of one or more virtual machines running on a virtual machine monitor, which in turn is running on underlying hardware with a segmented architecture.
2. Description of the Related Art
The operating system plays a special role in today's personal computers and engineering work stations. Indeed, it is the only piece of software that is typically ordered at the same time the hardware itself is purchased. Of course, the customer can later change operating systems, upgrade to a newer version of the operating system, or even re-partition the hard drive to support multiple boots. In all cases, however, a single operating system runs at any given time on the computer. As a result, applications written for different operating systems cannot run concurrently on the system.
Various solutions have been proposed to solve this problem and eliminate this restriction. These include virtual machine monitors, machine simulators, application emulators, operating system emulators, embedded operating systems, legacy virtual machine monitors, and boot managers.
Virtual Machine Monitors
Virtual machine monitors (VMM's) were the subject of intense research in the late 1960's and 1970's. See, for example, R. P. Goldberg, “Survey of virtual machine research,” IEEE Computer, Vol. 7, No. 6, 1974. During that time, moreover, IBM Corp. adopted a virtual machine monitor for use in its VM/370 system.
A virtual machine monitor is a thin piece of software that runs directly on top of the hardware and virtualizes all, or at least some subset of, the resources of the machine. Since the exported interface is the same as the hardware interface of the machine, the operating system cannot determine the presence of the VMM. Consequently, when the hardware interface is compatible with the underlying hardware, the same operating system can run either on top of the virtual machine monitor or on top of the raw hardware.
Virtual machine monitors were popular at a time where hardware was scarce and operating systems were primitive. By virtualizing all the resources of the system, such prior art VMMs made it possible for multiple independent operating systems to coexist on the same machine. For example, each user could have her own virtual machine running a single-user operating system.
The research in virtual machine monitors also led to the design of processor architectures that were particularly suitable for virtualization. It allowed virtual machine monitors to use a technique known as “direct execution,” which simplifies the implementation of the monitor and improves performance. With direct execution, the VMM sets up the processor in a mode with reduced privileges so that the operating system cannot directly execute its privileged instructions. The execution with reduced privileges generates traps, for example when the operating system attempts to issue a privileged instruction. The VMM thus needs only to correctly emulate the traps to allow the correct execution of the operating system in the virtual machine.
As hardware became cheaper and operating systems more sophisticated, VMM's based on direct execution began to lose their appeal. Recently, however, they have been proposed to solve specific problems. For example, the Hypervisor system provides fault-tolerance, as is described by T. C. Bressoud and F. B. Schneider, in “Hypervisor-based fault tolerance,” ACM Transactions on Computer Systems (TOCS), Vol. 14. (1), February 1996; and in U.S. Pat. No. 5,488,716 “Fault tolerant computer system with shadow virtual processor,” (Schneider, et al.). As another example, the Disco system runs commodity operating systems on scalable multiprocessors. See “Disco: Running Commodity Operating Systems on Scalable Multiprocessors,” E. Bugnion, S. Devine, K. Govil and M. Rosenblum, ACM Transactions on Computer Systems (TOCS), Vol.15, No. 4, November 1997, pp. 412-447.
Virtual machine monitors can also provide architectural compatibility between different processor architectures by using a technique known as either “binary emulation” or “binary translation.” In these systems, the VMM cannot use direct execution since the virtual and underlying architectures mismatch; rather, they must emulate the virtual architecture on top of the underlying one. This allows entire virtual machines (operating systems and applications) written for a particular processor architecture to run on top of one another. For example, the IBM DAISY system has recently been proposed to run PowerPC and x86 systems on top of a VLIW architecture. See, for example, K. Ebcioglu and E. R. Altman, “DAISY: Compilation for 100% Architectural Compatibility,” Proceedings of the 24th International Symposium on Computer Architecture, 1997.
General Shortcomings of the Prior Art
All of the systems described above are designed to allow applications designed for one version or type of operating system to run on systems with a different version or type of operating system. As usual, the designer of such a system must try to meet different requirements, which are often competing, and sometimes apparently mutually exclusive.
Virtual machine monitors (VMM) have many attractive properties. For example, conventional VMMs outperform machine emulators since they run at system level without the overhead and constraint of an existing operating system. They are, moreover, more general than application and operating system emulators since they can run any application and any operating system written for the virtual machine architecture. Furthermore, they allow modern operating systems to coexist, not just the legacy operating systems that legacy virtual machine monitors allow. Finally, they allow application written for different operating systems to time-share the processor; in this respect they differ from boot managers, which require a complete “re-boot,” that is, system restart, between applications.
As is the typical case in the engineering world, the attractive properties of VMMs come with corresponding drawbacks. A major drawback is the lack of portability of the VMM itself—conventional VMMs are intimately tied to the hardware that they run on, and to the hardware they emulate. Also, the virtualization of all the resources of the system generally leads to diminished performance.
As is mentioned above, certain architectures (so-called “strictly virtualizeable” architectures), allow VMMs to use a technique known as “direct execution” to run the virtual machines. This technique maximizes performance by letting the virtual machine run directly on the hardware in all cases where it is safe to do so. Specifically, it runs the operating system in the virtual machine with reduced privileges so that the effect of any instruction sequence is guaranteed to be contained in the virtual machine. Because of this, the VMM must handle only the traps that result from attempts by the virtual machine to issue privileged instructions.
Unfortunately, many current architectures are not strictly virtualizeable. This may be because either their instructions are non-virtualizeable, or they have segmented architectures that are non-virtualizeable, or both. Unfortunately, the all-but-ubiquitous Intel x86 processor family has both of these problematic properties, that is, both non-virtualizeable instructions and non-reversible segmentation. Consequently, no VMM based exclusively on direct execution can completely virtualize the x86 architecture.
Complete virtualization of even the Intel x86 architecture using binary translation is of course possible, but the loss of performance would be significant. Note that, unlike cross-architectural systems such as DAISY, in which the processor contains specific support for emulation, the Intel x86 was not designed to run a binary translator. Consequently, no conventional x86-based system has been able to successfully virtualize the Intel x86 processor itself.
The parent appli
Bugnion Edouard
Le Bich C.
Lim Beng-Hong
Ali Syed J.
An Meng-Al T.
Pearce Jeffrey
VMWare, Inc.
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