Abstract:
A method and apparatus for efficiently executing guest programs in a virtualized computing environment are presented. The method includes executing a virtual machine on a computing hardware; executing a single hypervisor in a first security ring on the virtual machine; executing a single guest program on the virtual machine, wherein the single guest program includes a single kernel being executed in the first security ring and at least one application being executed in a second security ring; and executing at least an instruction issued by the at least one application without trapping the single hypervisor.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/685,099 filed on Nov. 26, 2012, now allowed, which claims the benefit of U.S. Provisional Application No. 61/563,859 filed on Nov. 28, 2011, the contents of which are hereby incorporated by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present disclosure generally relates to virtual machines (VMs), and more specifically to the efficient execution of an application being executed as a guest on a VM. 
       BACKGROUND 
       [0003]    Hardware virtualization is the process of creating of a virtual machine that acts like a computer with an operating system. Software executed on these virtual machines is typically separated from the underlying hardware resources. A hypervisor is a program that allows guest virtual machines to run concurrently on a host computer. The hypervisor presents to the guests a virtual operating platform and manages the execution of the guest operating systems. Thus, multiple instances of a variety of operating systems may share the virtualized hardware resources. 
         [0004]    In the prior art there are described virtualization architectures having a hypervisor that are further extended to expose the hardware of the system to upper layers. Such extensions involve the use of, for example, nested virtualization where above a virtual platform an additional level of virtualization takes place. A typical nested virtualization environment includes three layers of virtualization over the hardware infrastructure: a host hypervisor, guest hypervisors, and VMs. Each of the guest hypervisors controls the execution of the plurality of VMs. In this architecture, each VM can execute one or more guest operating system (although VMs can execute also without having any guests too). The problem in such virtualization architecture is that this approach is very slow as many software components are involved in the execution of a guest OS or any application executed by the VM. 
         [0005]    As the guest OS runs in a limited memory address space, there is not enough space to access the full hardware, thus hardware emulation is required resulting in a significantly slower execution. For example, in the event the hypervisor needs to respond to a system call by a guest requires moving from one address space to another, traps are utilized for the purpose which results in duplication of execution environments. This happens because the move from one address space to another also involves a multitude of traps that require additional processing and hinder performance. Moreover, as hardware emulation in software is required, the overall performance is further reduced. 
         [0006]    Typically, a trap initiates a full operation that relinquishes control from the guest OS and transfers the control to the hypervisor. This involves, for example, switching from execution in Ring  0  to execution in Ring  3 , which entails significant overhead. The execution takes place at the hypervisor level and then needs to relinquish control to the guest, which again involves an overhead to reach back for Ring  0  execution. Rings or protection rings are hierarchical protection domains utilized to protect data and functionality from faults and malicious actions. Each protection provides different levels of access to hardware/software resources. In a typical operating system, the most privileged is the kernel or Ring  0  which interacts directly with the physical hardware (e.g., the CPU and memory), while the least privileged is Ring  3 . 
         [0007]    To further appreciate the complexity of handling the move from one level to another, one may also consider the case of a page fault at the guest. A page fault typically results in an exception to the firmware of the guest and from there an exception to the kernel moving to a different ring. Each such operation is very costly in terms of performance. One of the problems in handling page faults this way is the fact that there is no data of the guest OS in kernel (Ring  0 ), a potentially risky proposition that is solved at times by using segmentation limits. That way the user cannot see the data that is in the kernel. 
         [0008]    However, such support is not generally or otherwise efficiently available in modern 64-bit processors, and hence workarounds are needed. To this end, a limited number of instructions are available (typically for an X86® architecture being some thirteen instructions), however, the need for the monitoring of the workarounds when they occur results in significant overhead. 
         [0009]    Typical prior art solutions first check for all places in the code where it will be necessary to move between the guest and the hypervisor; such code is typically replaced by using a jump command. This is necessary because prior art solutions specifically deter from the execution of the kernel of the guest in the same security ring of that of an application executed by the guest. Therefore, prior art solutions typically execute at the kernel and the application of the guest at the same security ring, for example, Ring  3 , while the hypervisor is being executed, for example, in Ring  0 . An exemplary case for a long jump from the hypervisor and the kernel as well as application of the guest is shown in  FIG. 1 . 
         [0010]    It would be therefore advantageous to provide a solution that overcomes the deficiencies of the prior art. It would be further advantageous if such a solution maintains the security requirements of the various rings of the operating system. 
       SUMMARY 
       [0011]    Certain embodiments disclosed herein include a method for efficiently executing guest programs in a virtualized computing environment. The method comprises executing a virtual machine on a computing hardware; executing a single hypervisor in a first security ring on the virtual machine; executing a single guest program on the virtual machine, wherein the single guest program includes a single kernel being executed in the first security ring and at least one application being executed in a second security ring; and executing at least an instruction issued by the at least one application without trapping the single hypervisor. 
         [0012]    Certain embodiments disclosed herein also include an apparatus for efficiently executing a guest in a virtualized computing environment. The apparatus comprises: a processing unit; and a memory, the memory containing instructions that, when executed by the processing unit, configure the apparatus to: execute a virtual machine on a computing hardware; execute a single hypervisor on the virtual machine in a first security ring; execute a single guest program on the virtual machine, wherein the single guest program includes a single kernel being executed in the first security ring and at least one application being executed in a second security ring; and execute at least one instruction issued by the at least one application without trapping the single hypervisor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The subject matter disclosed herein is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other objects, features, and advantages of the disclosed embodiments will be apparent from the following detailed description taken in conjunction with the accompanying drawings. 
           [0014]      FIG. 1  is a schematic diagram of code execution using different protection rings for the guest&#39;s kernel and the hypervisor, requiring the use of a long jump upon a trap. 
           [0015]      FIG. 2  is a schematic diagram of a system according to an embodiment. 
           [0016]      FIG. 3  is a flowchart of the configuration of a guest on a system according to the principles. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The embodiments disclosed herein are only examples of the many possible advantageous uses and implementations of the innovative teachings presented herein. In general, statements made in the specification of the present application do not necessarily limit any of the various claimed embodiments. Moreover, some statements may apply to some inventive features but not to others. In general, unless otherwise indicated, singular elements may be in plural and vice versa with no loss of generality. In the drawings, like numerals refer to like parts through several views. 
         [0018]    According to various embodiments disclosed herein, a virtualized environment that includes a plurality of virtual machines (VMs) each of which executes a hypervisor being executed over a hardware infrastructure is provided. The hypervisor runs in a first security ring with a single guest being executed on each VM. The guest further comprises at least a software application being executed in a second security ring. 
         [0019]    The disclosed virtualized environment does not need to trap upon execution of certain instructions and move to the hypervisor with all the overhead that this requires, as it is assumed that the integrity and security is always maintained by the hypervisor of the respective VM. According to various embodiments disclosed herein, instead of moving between address spaces when the guest runs in a limited memory address space, the execution of the guest is performed within the same address space, e.g., in the guest space address. As a result no traps are necessary, and hence, operations that would result with a trap can be performed within the guest rather than in the hypervisor. This prevents the need of context switching in order to hop between the guest and hypervisor with all the overhead that this entails. 
         [0020]    Moreover, according to one embodiment, in the disclosed virtualized environment a hypervisor runs only a single guest. The advantage for a hypervisor to run a single guest is that it is not necessary to run protection mechanisms when moving from the hypervisor to the guest and vice versa. This is due to the fact that the hypervisor handles all the protection needs for the guest, thus there is no need to run additional protections at the guest level. Therefore, it is possible to avoid such protection checks at the guest level. This approach allows running the kernel of the guest in the same ring of that of the hypervisor. 
         [0021]      FIG. 2  depicts an exemplary and non-limiting schematic diagram of a system  200  implementing a virtualized environment according to one embodiment. The system  200  comprises a computer hardware  210  which typically includes at least a processor coupled to a memory. The computer hardware  210  includes a processor  212  and a memory unit  214  coupled to the processor  212 . The processor  212  may be a central processing unit (CPU) having one or more cores. The computer hardware  210  typically also includes other computing resources, such as a storage disk, a motherboard, a memory management unit, registers, I/O ports, a network interface card (NIC), a display adapter, and the like. 
         [0022]    The computer hardware  210  executes one or more virtual machines (VM)  220 , for example VMs  220 - 1 ,  220 - 2 , . . . ,  220 -N. Each VM  220  executes a hypervisor  240  in a first security ring, for example, security Ring  0 . According to a preferred embodiment, each VM  220  also executes a single guest  230 . For example, a VM  220 - 1  executes a guest  230 - 1 , a VM  220 - 2  executes a guest  230 - 2 , and so on. Each guest operating system  230 - i  (i=1, 2, . . . , N), comprises a single kernel  232 - i  and at least one guest application  234 - i . However, it should be noted that a plurality of applications may be executed by a guest  230 - i.    
         [0023]    According to one embodiment, the execution of the kernel  232 -i (i=1, 2, . . . , N) is in the security Ring  0 , the same as that of the respective hypervisor  240 - i . Therefore, the responsibility for the integrity and security of execution of a guest  230 - i  of a VM  220 - i  is performed solely by the hypervisor of the respective VM  220 - i . Thus, the hypervisor of the VM  220 - i  is not required to duplicate the work on the kernel  232 - i . Moreover, as a result of this architecture, it is not necessary to perform the traps and/or the long jumps. 
         [0024]    It should be noted that running a kernel  232 - i  of a guest operating system  230 - i  and the hypervisor of the respective VM  220 - i  in the same security ring requires, for example, changing the stacks within the same ring. This is required because moving between rings would typically be automatically handled by the processor. However, the execution of the kernel  232 - i  and the VM firmware in the same ring provides performance advantages that significantly outweigh the impact of the additional functions that need to take place as a result of executing the kernel and the hypervisor in the same ring. The fact that moving from the VM firmware to the kernel and back involves a simple jump command ensures this performance advantage. 
         [0025]    In yet another embodiment, due to the particular nature of a single guest with respect of the hypervisor, it is possible to allow a guest operating system  230 - i  to change hypervisor data. This eliminates the lengthy and costly process of going back to the hypervisor and then back to the guest by means of the long jumps, thus the data can be directly checked without harming the integrity of the system. In one embodiment, the exceptions are received from a given ring where the guest is executed and remain therein. Therefore, all the overhead associated with the movement between rings is avoided, thereby improving the performance of the executed software. 
         [0026]    The execution of the guest, according to one embodiment, requires checking each and every instruction to determine at least if a change to the executed code is required. When access is made that requires a change to the code executed, a regular move operation is used rather than a long move, i.e., a move that goes out of the address space of the guest operating system. 
         [0027]    Moreover, the execution of the instruction continues within the same ring in which the guest is currently executed. Hence, the transfer into the VM kernel space of the guest operating system is significantly improved. 
         [0028]    In another embodiment, when the jump is performed, the hypervisor  240 - i  checks the code and makes the necessary operations and then returns to the regular operation without moving between rings and without degrading the overall protection or integrity of the system. The hypervisor  240 - i  uses a hash table to determine the return address to ensure proper execution. 
         [0029]    It should be noted that in the case of a move instruction in the code it is necessary to perform the process described hereinabove. However, as the jump may occur multiple times the overhead of going each time through the process, while not prohibitive, is undesirable. Therefore, according to an embodiment, the jump instruction is identified on a subsequent case and not directed immediately to the place determined previously to be the jump address for the jump instructions, using information stored in the cache. The cache may be part of a memory unit  214 . This prevents the need to have the hypervisor intervention thereby saving further overhead, as execution fairly quickly becomes close to native execution, once all jump instructions are cashed. 
         [0030]      FIG. 3  is an exemplary and non-limiting flowchart  300  illustrating the configuration of a guest on a system according to one embodiment. In S 310 , a request is received to start a guest OS on a system, for example, system  200 . In S 320 , it is checked whether there is a VM  220  being executed on the system  200  that does not currently have any other guest executed thereon, and if so execution continues with S 340 . Otherwise, in S 330 , a new VM  220  is instantiated on the computing hardware  210 , with a hypervisor executed in a first security ring, for example, Ring  0 . In S 340 , the guest, for example guest  230 - 1 , is instantiated on the respective VM  220 , for example, VM  220 - 1 , with its kernel (e.g., kernel  232 - i ) also executed in the first security ring, for example, Ring  0 . In addition, the applications of the guest  230 - 1  are executed in a second security ring, for example, Ring  3 . In S 350 , it is checked whether more requests are to be handled, and if so execution continues with S 310 ; otherwise, execution terminates. 
         [0031]    It should be understood that the execution of the kernel of the guest  230  and the respective hypervisor of the VM  220  in the same security ring provide the advantages described hereinabove, and provide superior performance and usage of computing resources. It should be further noted that the advantages discussed herein are of particular value in a nested virtualization environment as such environments would otherwise require significant overhead in their execution, which is prevented when using the embodiments discussed herein. 
         [0032]    The various embodiments disclosed herein may be implemented as hardware, firmware, software, or any combination thereof. Moreover, the software is preferably implemented as an application program tangibly embodied on a program storage unit or computer readable medium consisting of parts, or of certain devices and/or a combination of devices. The application program may be uploaded to, and executed by, a machine comprising any suitable architecture. Preferably, the machine is implemented on a computer platform having hardware such as one or more central processing units (“CPUs”), a memory, and input/output interfaces. The computer platform may also include an operating system and microinstruction code. The various processes and functions described herein may be either part of the microinstruction code or part of the application program, or any combination thereof, which may be executed by a CPU, whether or not such computer or processor is explicitly shown. In addition, various other peripheral units may be connected to the computer platform such as an additional data storage unit and a printing unit. Furthermore, a non-transitory computer readable medium is any computer readable medium except for a transitory propagating signal. 
         [0033]    All examples and conditional language recited herein are intended for pedagogical purposes to aid the reader in understanding the principles of the disclosure and the concepts contributed by the inventor to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments disclosed herein, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure.