Methods and systems are provided to control the execution of a virtual machine (VM). A VM Monitor (VMM) accesses VM Control Structures (VMCS) indirectly through access instructions passed to a processor. In one embodiment, the access instructions include?VMCS?component identifiers used by the processor to determine the appropriate storage location for the?VMCS?components. The processor identifies the appropriate storage location for the?VMCS?component within the processor storage or within memory.

TECHNICAL FIELD

Embodiments of the present invention relate generally to computer systems and more specifically to the operational control of virtual machines within computer systems.

BACKGROUND INFORMATION

A virtual machine architecture logically partitions a physical machine, such that the underlying hardware of the machine is time-shared and appears as one or more independently operating virtual machines (VMs). A Virtual Machine Monitor (VMM) runs on a computer and facilitates for other software the abstraction of one or more VMs. Each VM may function as a self-contained platform, running its own operating system (OS) and application software. The software running in a VM is collectively referred to herein as guest software.

The guest software expects to operate as if it were running on a dedicated computer rather than in a VM. That is, the guest software expects to control various events and have access to hardware resources on the computer (e.g., physical machine). The hardware resources of the physical machine may include one or more processors, resources resident on the processors (e.g., control registers, caches, and others), memory (and structures residing in memory, e.g., descriptor tables), and other resources (e.g., input-output devices) that reside in the physical machine. The events may include interrupts, exceptions, platform events (e.g., initialization (INIT) or system management interrupts (SMIs), and the like).

The VMM may swap guest software state in and out of the devices, memory and the registers of the physical machine as needed. The VMM may enhance performance of a VM by permitting the direct access to the underlying physical machine. This may be especially appropriate when an operation is being performed in non-privileged mode in the guest software, which limits software access to the physical machine or when operations will not make use of hardware resources in the physical machine which the VMM wishes to retain control.

The VMM regains control whenever a guest operation may affect the correct execution of the VMM or any of the non-executing VMs. Usually, the VMM examines such operations, determining if a problem exists before permitting the operation to proceed to the underlying physical machine or emulating the operation on the behalf of a guest. For example, the VMM may need to regain control when the guest accesses I/O devices, when it attempts to change machine configuration (e.g., by changing control register values), when it attempts to access certain regions of memory, and the like.

Existing systems that support VM operation, control the execution environment of a VM using a fixed format structure, herein referred to as a Virtual Machine Control Structure (VMCS). The?VMCS?is stored in a region of memory and contains, for example, state of the guest, state of the VMM, and control information indicating under which conditions the VMM wishes to regain control during guest execution. The processor(s) in the physical machine reads information from the?VMCS?to determine the execution environment of the VM and VMM, and to constrain the behavior of the guest software under control of the VMM.

Conventional architectures locate the?VMCS?in the memory of the physical machine and allow the VMM to access it using ordinary memory read and write instructions. For this reason, the format of the?VMCS?must be defined architecturally in the processor instruction set architecture (and documented in specifications and manuals in a manner similar to other system structures and instruction encodings). The VMM is coded directly to these specifications. This structuring limits the flexibility in implementation of the processor(s) supporting the VMM. Since the form of the?VMCS?is architecturally-defined, the microarchitecture of a particular processor implementation may not make changes in the format, contents, organization, or storage requirements of the VMCS?data for reasons of performance, extensibility, compatibility, security, and the like, without also requiring corresponding modifications to the installed base of VMM implementations.

Therefore, there is a need for more flexible implementations of virtual machine architectures, which are not rigidly coupled to the underlying implementation of the physical machines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1?is a diagram of a VM architecture, in accordance with one embodiment of the invention.

FIG. 2?is a flow diagram of a method to control a VM, in accordance with one embodiment of the invention.

FIG. 3?is a diagram of a?VMCS?access instruction, in accordance with one embodiment of the invention.

FIG. 4?is a flow diagram of a method to read data from a?VMCS, in accordance with one embodiment of the invention.

FIG. 5?is a flow diagram of a method to write data to a?VMCS, in accordance with one embodiment of the invention.

DESCRIPTION OF THE EMBODIMENTS

A novel VM control architecture is described. In the following detailed description of the embodiments, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration, but not limitation, specific embodiments of the invention may be practiced. These embodiments are described in sufficient detail to enable one of ordinary skill in the art to understand and implement them, and it is to be understood that other embodiments may be utilized and that structural, logical and electrical changes may be made without departing from the spirit and scope of the present disclosure. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the embodiments of the inventions disclosed herein is defined only by the appended claims.

A VMM presents to other software ("guest software," "guests," or simply "guest") the abstraction of one or more VMs. The VMM can provide the same or different abstractions to the various guests. Each guest expects the full facilities of the hardware platform presented in the VM to be available for its use. For example, the guest expects to have access to all registers, caches, structures, I/O devices, memory, and the like, according to the architecture of the processor and platform presented in the VM. Further, each guest expects to handle various events such as exceptions, interrupts, and platform events (e.g., initialization (INIT) and system management interrupts (SMIs).

Some of these resources and events are "privileged" because they must be managed by the VMM to ensure proper operation of VMs and to protect the VMM and other VMs. For the privileged resources and events, the VMM facilitates functionality desired by guest software while retaining ultimate control over these resources and events. The act of facilitating the functionality for the guest software may include a wide variety of activities on the part of the VMM. The activities of the VMM, as well as its characteristics, do not limit the scope of various embodiments of the present invention.

When guest software accesses privileged resources or a privileged event occurs, control may be transferred to the VMM. The transfer of control from the guest software to the VMM is referred to as a VM exit. After facilitating the resource access or handling the event appropriately, the VMM may return control to the guest software. The transfer of control from the VMM to the guest software is referred to as a VM entry.

The Virtual Machine Control Structure (VMCS) is an architecturally-defined structure containing, for example, state of the guest software, state of the VMM, control information indicating under which conditions the VMM wishes to prevent the guest from executing, and information regarding the most recent VM exit. In current systems, a representation of the?VMCS, which exactly matches the architecturally-defined structure, is located in memory. The processor in the physical machine reads information from the?VMCS?to determine the execution environment of the VM and to constrain its behavior.

During guest execution, the processor consults the control information in the VMCS?to determine which guest actions (e.g. execution of certain instructions, occurrence of certain exceptions, etc.) and events (e.g. external interrupts) will cause VM exits. When a VM exit occurs, components of the processor state used by guest software are saved to the?VMCS?and components of the processor state required by the VMM are loaded from the?VMCS. When a VM exit occurs, control is passed to the VMM?120?using any mechanism known to one of ordinary skill in the art.

When a VM entry occurs, the processor state that was saved at the VM exit (and which may have been modified by the VMM) is restored and control is returned to the guest software. To facilitate the first VM entry to a guest, the VMM writes appropriate guest state to the?VMCS. While processing a VM exit, the VMM may change a guest state in the?VMCS. In some embodiments, multiple?VMCS?structures supporting multiple VMs are managed by a single VMM on a single physical machine. The?VMCS?need not include all the information described above and can include additional information that assists in the control of the VM. In some embodiments, a?VMCS?can contain a significant amount of additional information.

FIG. 1?illustrates a diagram of a VM architecture?100, in accordance with one embodiment of the invention. The VM architecture?100?includes a base hardware platform?110?(e.g., physical machine). The base hardware platform?110?includes one or more processors?112?each having access to volatile and/or non-volatile memory?116. Additionally, there may be other elements in the base hardware platform that are not shown in?FIG. 1?(e.g., input-output devices). The VM architecture100?also includes a VMM?120?that manages one or more VMs (e.g.,?130,?140, and?150), where each VM (e.g.,?130,?140, and?150) supports one or more OSs (e.g.,?150,?160, and?170) and applications (e.g.,?152,?162, and?172). The processors112?can be any type of processor capable of executing software, such as a microprocessor, digital signal processor, microcontroller, or the like. The processors?112?may include microcode, programmable logic or hardcoded logic for performing the execution of method embodiments of the present invention.

Memory?116?can be a hard disk, a floppy disk, random access memory (RAM), read only memory (ROM), flash memory, any combination of the above devices, or any other type of machine medium readable by processor?112. Memory?116?may store instructions or data for performing the execution of method embodiments of the present invention. The memory?116includes a?VMCS?region?118?for use by the processor?112?in maintaining the state of the?VMCS, described in more detail below.

The processors?112?can be any type of processor capable of executing software, such as a microprocessor, digital signal processor, microcontroller, or the like. Each processor?112?may include a?VMCS?cache?114, which is described in more detail below. The processors?112?may include microcode, programmable logic or hard coded logic for performing the execution of method embodiments of the present invention.

If it is present, the?VMCS?cache?114?may be used to store some or all of the?VMCS?state either temporarily or throughout its lifetime. The?VMCS?cache?114?can include registers, cache memory, or any other storage. In?FIG. 1, the?VMCS?cache114?is shown as part of the processor?112, but it may reside outside of the processor?112?within any component of the bare platform hardware?110. In discussions that follow, the?VMCS?cache?114?is also referred to as "on-processor storage" or "on-processor resources", but it should be understood that this storage may reside in platform components other than the processor?112. The?VMCS?cache?114?is not strictly required for implementing the methods of this invention.

Conventionally, a VMM would access a?VMCS?in memory using ordinary read and write instructions. In the VM architecture100?of?FIG. 1, however, the VMM?120?accesses the?VMCS?region?118?indirectly through a set of processor-provided VMCS?access instructions?119. The?VMCS?access instructions?119?make use of the?VMCS?region?118?and any available VMCS?cache?114. In an embodiment,?VMCS?access instructions?119?include an operand that is an identifier for the?VMCS component that is being accessed. The identifier is referred to herein as a "component identifier." The VMM?120?does not need to be aware that any particular?VMCS?component is stored in the?VMCS?region?118?or in the?VMCS?cache?114. The VM architecture?100?further provides that if ordinary read and write instructions are used to access the?VMCS?region?118, unpredictable results may occur. The use of the?VMCS?access instructions?119?gives the processor?112?freedom in its usage of available on-processor and memory based (e.g., the?VMCS?region?118) storage and also allows for a variety of performance optimizations.

In some embodiments, the?VMCS?access instructions?119?are implemented by the processor microarchitecture by reading and writing memory in the?VMCS?region?118. In other embodiments, the?VMCS?access instructions?119?may read and/or write on-processor resources. The VMM?120?need not be aware of how the underlying physical machine microarchitecture is supporting the?VMCS. In this way, the underlying processor implementation can be altered to accommodate performance, security, reliability, or other considerations without rendering the VMM?120?incompatible with the underlying processor implementation, and customized?VMCS?implementations can be developed for each processor implementation.

The following example illustrates the drawback of a VM architecture that does not employ?VMCS?access instructions?119. If a processor implementation can temporarily cache?VMCS?data in on-processor storage, only writing data to the in-memory VMCS?region?118?when a particular event occurs. During the period of time where the?VMCS?data is cached, an ordinary read to the?VMCS?region?118?will return a stale value (an incorrect value). An ordinary write to?VMCS?region?118?will not update data in on-processor storage unless special precautions are taken by the processor implementation to properly map the write to the storage. Without the use of?VMCS?access instructions?119, the processor implementation must keep the VMCS?region consistent with any temporary or cached state stored in on-processor resources; this may preclude certain performance optimizations, extensions of the VM architecture, etc. as is discussed further below. In contrast to the ordinary memory operations,?VMCS?read instructions return a value stored in on-processor if appropriate and?VMCS?write instructions properly update the?VMCS?state, wherever it is located. These instructions are described in detail below.

To facilitate the?VMCS?access instructions?119, each element of the?VMCS?is identified by an architecturally-defined constant that identifies the component of the?VMCS; these constant values are referred to herein a "component identifiers." In an embodiment, the component identifier is a 16 bit value, but may be larger or smaller in other embodiments.

In the discussions that follow, a number of fields in the?VMCS?are used in descriptions of various embodiments of the invention. For example, GUEST_EIP is the field containing the instruction pointer for the guest software; VM_CONTROLS is the field containing bits that control the VM execution environment, etc. An understanding of the syntax and semantics of the various fields is not necessary to understand the invention described here. Additionally, the fields are given specific architecturally-defined component identifiers. The specific fields used and the values of the component identifiers in these examples should not limit the applicability of the invention in any fashion.

An illustration of the advantage of the use of?VMCS?access instructions?119?is as follows. Consider that a processor implementation may change the layout of data stored in the?VMCS?region?118?from one processor implementation to another. For example, a first processor implementation may store the GUEST_EIP field of the?VMCS?region starting at the 28^th?byte of the?VMCS?region. A second processor implementation may store the same?VMCS?field at the 16^th?byte in the VMCS?region. A VMM?120, written for an initial implementation and utilizing the?VMCS?access instructions?119, will still be functional on the latter implementation of the processor?112?even though the layout of the?VMCS?region?118?has changed. This compatibility is achieved because the implementation of the?VMCS?access instructions in the two processor implementations comprehend the layout of the?VMCS?region?118?used and appropriately access the necessary data.

In some embodiments, to facilitate the?VMCS?access instructions?119, the VMM?120?can be required to set aside a memory region (e.g.,?VMCS?region?118) to accommodate all or part of the storage required by the processor?112?for the VMCS. In these embodiments of the invention, a processor-provided instruction will permit the VMM?120?to provide a pointer or address of the?VMCS?region?118?to the processor?112. In an embodiment, the address is a physical address. Other embodiments may use virtual or linear addresses. The address provided to the processor?112?using this instruction is hereafter referred to as a?VMCS?pointer. This instruction informs the processor?112?of the location of the?VMCS?region?118. This new instruction makes active a?VMCS?that may be stored by the processor?112?in whole or in part in the?VMCS?region118?referenced by the?VMCS?pointer.

Another embodiment can provide a mechanism that allows the VMM?120?to discover the amount of memory?116?that must be reserved for a?VMCS?region?118. For example, in the processor instruction set architecture (ISA) of the Intel Pentium IV (referred to herein as the IA-32 ISA), a Model Specific Register (MSR) can be provided that includes the required?VMCS region size. Another embodiment provides an instruction that returns the required?VMCS?region size. Any other mechanism available may be used to convey this information to the VMM. In this way, the size of the required memory region?118?can change from processor implementation to processor implementation, without forcing a redesign or recompilation of the VMM?120.

For example, suppose that a first processor?112?requires 64 bytes for the?VMCS?region?118?in memory?116. This requirement is reported to the VMM?120?as described above. A VMM?120?is written to run on this processor implementation, using the mechanism described above to determine how much memory?116?to allocate for the?VMCS region?118. A second processor implementation is created that now requires 128 bytes for?VMCS?storage in memory?116. The VMM?120?written for the first processor implementation will function correctly on the second implementation because it will allocate the correct amount of storage for the?VMCS?region?118.

While the?VMCS?pointer is active, the processor?112?can store all or part of the?VMCS?in the?VMCS?region?118?or, alternatively, in resources residing on the processor?112?or in any other available location (i.e., in the?VMCS?cache?114). Additionally, the processor?112?can store non-architectural state information in the?VMCS?region?118, or in on-processor resources. For example, the processor?112?can store temporary variables, microarchitectural states associated with a VM (e.g.,?130,?140, or?150), indicators of the state of the VM (e.g.,?130,?140, or?150), and the like. Software does not use ordinary memory reads and writes to access the?VMCS?region?118?while the?VMCS?pointer is active. This restriction ensures the correctness of the operation of the VMM?120?and the VM (e.g.,?130,?140, or?150) associated with the?VMCS.

Another processor-provided instruction writes any?VMCS?data that was cached in on-processor resources to the?VMCS region?118, invalidates the appropriate data in on-processor storage and further deactivates the?VMCS?pointer. An embodiment may mark the?VMCS?as inactive by, for example, writing a status indicator that is architecturally or non-architecturally-defined to the?VMCS?region. Another embodiment may simply flush on-processor storage and deactivate (invalidate) on-processor state for the?VMCS. This instruction is executed prior to any attempt by the VMM?120?to move the contents of the?VMCS?region?118. When a VMM?120?attempts to move the?VMCS?region?118?it can do so with a single data-block move because the?VMCS?format is maintained and known only to the processor implementation. Additionally, this block move is possible because the VMM is aware of the size of the?VMCS?region (having allocated the memory based on the mechanisms described here). Individual elements of the?VMCS?need not be discernable to the VMM?120.

In some embodiments, a mechanism specific to a particular embodiment can permit the VMM?120?to identify the processor implementation that established a particular?VMCS. The VMM?120?can use this processor identification to determine if the VMCS?is compatible with another processor implementation. In one embodiment, this identifier is located in the first 4 bytes of the?VMCS?region?118?and reported to the VMM?120, for example, in an MSR or through any other method. Prior to the first use of a?VMCS, the VMM?120?can be required to write this identifier into the appropriate location in the?VMCS?and hence the format of that part of the?VMCS?region?118?can be architecturally defined. It is desirable, in some embodiments, that all implementations define identical architecturally-defined portions of the?VMCS?region?118.

Other embodiments can define new architecturally-defined portions of the?VMCS?region?118?provided previous embodiments have left the newly defined areas undefined and the newly defined portions do not interfere with the operation of a VMM?120?which does not make explicit use of them. In this way, any VMMs?120?written for these embodiments will be operational on the newer implementations.

In some embodiments the processor-provided instructions?119?include a number of distinct instructions:

• ?
• A?VMCS?load-pointer instruction has a memory address as an operand. This address is the location at which the processor?112?can store the?VMCS?(e.g., the beginning of the?VMCS?region?118). The?VMCS?associated with this address is made active by the instruction. This instruction also allows for activation of a VM (e.g.,130,?140, or?150) associated with and controlled by the?VMCS?and the use of various other instructions described below. In an embodiment, the address is a physical address. Other embodiments may use virtual or linear addresses.
• A?VMCS?store-pointer instruction stores a pointer to the active?VMCS?region?118?into a register (e.g., on the processor?112) or a memory location (e.g., in the memory?116); the location of such storage location may be provided as an operand to the instruction.
• A?VMCS?read instruction reads a component of the?VMCS?into a register (e.g., on the processor?112) or a memory location (e.g., in the memory?116). The instruction may include a number of parameters, including a component identifier indicating the?VMCS?component that is to be read from the?VMCS?and the location (e.g., register or memory location) where the data read from the?VMCS?is to be stored.
• A?VMCS?write instruction loads a component of the?VMCS?from a register (e.g., on the processor?112) or a memory location (e.g., in the memory?116). Like the?VMCS?read instruction, a?VMCS?write instruction may include operands for the?VMCS?component identifier. Additionally, it may include an operand describing the location (e.g., register or memory location) of the data to be written to the?VMCS.
• A?VMCS?clear instruction ensures the contents of all on-processor storage associated with the?VMCS?are stored back into the?VMCS?region?118, invalidates data in on-processor resources and further deactivates the VMCS?pointer. This instruction can operate without operands, flushing and deactivating a currently active VMCS?pointer, or, in an alternative embodiment, it may take as an operand the?VMCS?pointer for which flushing and deactivation is required. In an embodiment, a?VMCS?clear instruction may mark the?VMCS?as inactive by, writing a status indicator that is architecturally or non-architecturally-defined to the?VMCS?region.
• Finally, a?VMCS?enter instruction causes a transfer of control (i.e. a VM entry) to the VM (e.g.,?130,?140, or150) defined by the active?VMCS, by loading a processor state according to the semantics of the VM architecture?100?and the contents of the?VMCS. Alternatively, the instruction may include an argument with the VMCS?pointer (or the location of said pointer) that is to be entered.

The processor-provided instructions?119?described above represent only one embodiment, since a variety of different or alternative instructions?119?can be provided. For example, in some embodiments, the?VMCS?clear instruction may copy VMCS?data from on-processor storage to the?VMCS?region?118?without deactivating the?VMCS?pointer. Operands can be explicit or implicit. Other instructions?119?can be provided (or variants on the instructions?119?presented above) that act on all?VMCS?pointers active in the processor?112, and the like.

As one of ordinary skill in the art appreciates, conventional VM architectures have a static, architecturally-defined form for the?VMCS?in memory. This limits the ability of the processor implementations to augment or change the size, organization, or contents of the?VMCS?because changes to the?VMCS?would require corresponding changes to the VMM implementations. Additionally, since conventional VMMs access conventional VMCSs using ordinary memory read and write operations, the processor implementation has less flexibility in allocating storage of the?VMCS?data to on-processor resources. For example, the processor may be unable to cache certain portions of the?VMCS?in on-processor resources during VM exit to the VMM, because the processor may have difficulty detecting if the VMM has made modifications to the corresponding areas of the?VMCS?in memory. This inability to ascertain coherency between on-processor resources and the in-memory?VMCS?images complicates error and consistency checking that may be required prior to executing guest software following a VM entry.

However, with various embodiments of the present invention, VMMs?120?do not access the?VMCS?memory image directly using ordinary memory read and write operations, do not utilize a pre-defined format for the?VMCS?in memory?116, and determine the required storage size for the?VMCS?in memory?116?at run-time.

Run-time binding of?VMCS?storage memory requirements and the use of the processor provided instructions?119, described above, is illustrated in?FIG. 2.?FIG. 2?illustrates the state of the?VMCS?pointer through a variety of activities in the VMM. Processing starts in block?210. At this time, there is no active?VMCS?pointer. In block?210, the VMM determines the size of the memory region required by the processor to support the?VMCS. As described above, this may be accomplished by, for example, reading a designated MSR.

In block?220, the VMM allocates the required memory; the?VMCS?pointer is still inactive. Although optimally this memory region is contiguous within physical memory, it is apparent to one of ordinary skill in the art that no such requirement is necessary with this embodiment. The VMM activates the?VMCS?by providing the address of the?VMCS?region to the processor using the?VMCS?load-pointer instruction, described above (entering block?230). At this point, the?VMCS?pointer is called a working?VMCS?pointer. After the?VMCS?pointer is active, the VMM may read and write components of the?VMCS using the appropriate?VMCS?access instructions (shown in?FIG. 1?as?119?and in?FIG. 2?as?232?and?234). Following these read or write operations, the?VMCS?pointer remains active.

When the VMM wishes to allow the guest to execute, it uses the VM entry instruction to load the guest into the machine (entering block?240). After the VM entry, the?VMCS?pointer is still active, but now functions as a controlling?VMCS?pointer, used by the processor to determine the guest execution environment and behavior.

When a VM exit occurs, control returns to the VMM (returning to block?230?from block?240). The?VMCS?pointer remains active, again as a working?VMCS?pointer; the VMM can read and write?VMCS?fields (arrows?232?and?234) as appropriate and can enter the guest again using the VM enter instruction (returning to block?240). Alternatively, the VMM may deactivate the?VMCS?pointer using the VM clear instruction, at which time the?VMCS?pointer becomes inactive (returning to state?220).

Note that method?200?is not limited to any particular sequence of operations since the VMM may perform a variety of operations (e.g., VM read, VM write, VM enter, etc.) at any particular moment in time. Additionally, at any particular moment in time within a given processor utilizing method?200, a single?VMCS?pointer or a variety of?VMCS?pointers can be active or inactive. In some embodiments, multiple VMCSs can be active within any given processor at any particular point in time. In this way a VMM can switch between VMs without executing a?VMCS?clear instruction, thereby improving VM processing efficiency.

In an embodiment, an additional processor-provided instruction may provide the VMM with the ability to query and obtain the number of concurrent or parallel VMCSs that can be active at any particular point in time. Other embodiments can provide an MSR that the VMM may read to obtain this information. In an alternative embodiment, the number of?VMCS pointers that can be active simultaneously (and hence can, for example, be cached in on-processor resources) may not be directly visible to the VMM software, with the processor implementation automatically handling overflow conditions when a VMM activates more?VMCS?pointers than the processor can store in on-processor resources. In this case, the processor can automatically flush appropriate?VMCS?data to associated?VMCS?regions in memory. In some embodiments, explicit VMCS?pointer arguments may be required within a number of the processor-provided instructions described above with the discussion of?FIG. 1.

Embodiments of the present invention remove requirements on software to manage the details associated with managing on-processor and in-memory storage of?VMCS?data. Thus, the VMM manages each of the VMs under its control at a higher level of abstraction. This strategy permits the processor-provided instructions, discussed above in?FIG. 1?and?FIG. 2, to manage the details of?VMCS?storage such that VM execution is more affordably and optimally altered or extended by adding or modifying the processor-provided instructions without changing existing VMM software.

FIG. 3?is a diagram depicting the use of the?VMCS?read/write instruction in an embodiment of the present invention. The architectural?VMCS?format?305?is shown, though it is not used explicitly by the VMM; rather, the VMM is programmed with knowledge of the?VMCS?component identifiers, field sizes and field semantics, but not with an architectural definition of the form of the?VMCS?storage in memory. When a VMM desires to access a field in the architectural?VMCS?305, it performs a VMCS?read (or?VMCS?write, as appropriate; only?VMCS?read is shown in?FIG. 3?for illustrative purposes only). A parameter to the?VMCS?read instruction?310?is a component identifier, which is an architecturally-defined constant that identifies the component of the?VMCS. The processor uses the component identifier to map to on-processor (e.g., the VMCS?cache?322) or in-memory resources (e.g., the?VMCS?region?324) as appropriate to access the?VMCS?data on behalf of the VMM using a mapping function?320. If the data stored in the?VMCS?region or?VMCS?cache is not in the architecturally-defined format, the data is appropriately reformatted to match using a reformatting function?323.

Two example?VMCS?access instructions are shown in?FIG. 3. Though both of these examples are for?VMCS?read instructions, a similar set of activities occurs for?VMCS?write instructions as is detailed in discussions below regarding?FIG. 5.

Referring to?FIG. 3, a first example?VMCS?read instruction?310?accesses the GUEST_ESP component, which has an architecturally-defined encoding of 0x4032. The processor implementation maintains data for this component in the?VMCS region?324, as determined by the mapping function?320. The processor reads the appropriate component data from the VMCS?region?324?using a memory read operation?330. The read operation?330?understands the location of the component in the?VMCS?region?324?(again, as determined by the mapping function?320; in this example, it is located at offset?12?in the VMCS?region). The processor then returns the data value to the VMM (shown as arrow?331).

A second example?VMCS?read instruction?350?accesses the VM_CONTROLS component, which has an architecturally-defined encoding of 0x1076. This processor implementation maintains this component in the?VMCS?cache?322?(as determined by the mapping function?320). The processor accesses the?VMCS?cache?322?to retrieve the data. In this case, the data is stored on-processor in a form that does not match the architectural definition of the VM_CONTROLS component (e.g., the data is stored on-processor as a reordered 8 byte object, whereas the architectural definition of the VM_CONTROLS field is a 4 byte object). The processor, prior to returning data to the VMM, reformats the VM_CONTROLS data to match the architectural definition of the field using reformatting function?323. This reformatted value (i.e. the value that matches the architectural definition of the requested component) is returned to the VMM (shown as arrow?326).

Using these?VMCS?access instructions, a VMM, managing one or more VMs each identified by a separate?VMCS, is not required to manage the storage associated with a?VMCS?as it is cached from memory to on-processor resources. Additionally, the VMM does not need to manage changing processor implementation details, such as the formatting of data in memory or in on-processor resources. Thus, processor developers may alter or modify the?VMCS?access instructions to improve VM performance and extend VM capabilities without adversely affecting the operation of existing VMMs or VMs. Existing VMMs and VMs may benefit from such alterations, however, as performance, reliability, scalability or other improvements are brought to new implementations of the VM architecture.

FIG. 4?is a flowchart of a method?400?for execution of a?VMCS?read instruction, according to one embodiment of the present invention. In?410, a?VMCS?read request is received from a VMM. In?420, the?VMCS?component identifier is acquired from the?VMCS?read request. The component identifier is an architecturally-defined constant that identifies the desired component of the?VMCS.

A processor inspects the component identifier in?430?to determine if the?VMCS?component associated with the component identifier is in memory. If the?VMCS?component is stored in memory then the address of the memory location is calculated in?440, and the?VMCS?data associated with the?VMCS?component is acquired in?450. However, if the?VMCS?component is not stored in memory, then the processor acquires the?VMCS?data associated with the?VMCS?component from on-processor storage in?460. In this way, the processor uses the component identifier to map the read request to the?VMCS component storage, whether it resides in memory or in on-processor storage.

In?470, a check is made by the processor to determine if a reformatting of the?VMCS?data is required before returning the VMCS?data to the VMM. If the?VMCS?data is stored (either in the?VMCS?region or in on-processor resources) in the format which differs from the architecturally-defined data format for the?VMCS?component (i.e. the?VMCS?component is stored in an implementation-specific data format which differs from the architecturally-defined format), then, in?480, a reformatting function is accessed to translate the implementation-specific?VMCS?data into an architecturally-defined data format. If the VMCS?data is stored (either in the?VMCS?region or in on-processor resources) in the architecturally-defined data format for the?VMCS?component, then no reformatting function or translation on the?VMCS?data need occur. Finally, in?490, the?VMCS data (now in the architecturally-defined data format) is returned to the VMM.

FIG. 5?is a flowchart of a method?500?for execution of a?VMCS?write instruction, according to one embodiment of the present invention. In?505, a processor receives a?VMCS?write request from a VMM. The processor acquires as one of the operands of the write request the component identifier, as depicted in?510. Moreover, in?515, the processor acquires, as another operand, the write data that it is desired to be written to the?VMCS. This write data is in the architecturally-defined data format for the?VMCS?component being written.

In?520, a check is made to determine if the?VMCS?component is stored in an architecturally-defined data format by the processor (in the?VMCS?region or in on-processor resources). Accordingly, if the?VMCS?component is not stored in the architecturally-defined data format, then, in?525, the appropriate reformatting of the data is performed so that the data is in the appropriate implementation-specific data format associated with the?VMCS?component being accessed. The format in which data is stored may be identical to the architecturally-defined format, or it may differ in size or organization.

Next, in?530, another check performed to determine the location at which the?VMCS?component is stored by the processor. Using the component identifier, the processor determines where the storage for the?VMCS?component is located. If the storage location is in memory, then, in?535, the memory address is calculated, and, in?540, the write data is written to the memory location. However, if the storage location is not in memory, then, in?545, the appropriate location in on-processor storage is determined, and the write data is written to the on-processor storage. The data written to the storage is in the implementation-specific data format, which may be the same or different than the architecturally-defined format, depending on the?VMCS?component in question, the processor implementation, and, in some embodiments, on whether the component in question is currently store in on-processor resources or in the?VMCS?region.

The mechanism used in processes?400?and?500?to determine the storage location for a particular?VMCS?component and to determine if the?VMCS?component is stored in the architecturally-defined data format by the processor are implementation specific. In an embodiment, the processor utilizes a lookup table that is indexed by the component identifier. Additionally, note that if multiple?VMCS?pointers may be active simultaneously, these determinations may depend on which?VMCS?is being accessed.

SRC=https://www.google.com.hk/patents/US7318141

Methods and systems to control virtual machines