Vmware, Inc.

Rohit Jain

Daniel J Scales

Boris Weissman

Jeffrey W Sheldon

Ganesh Venkitachalam

Vyacheslav Vladimirovich Malyugin

Min Xu

System and method for providing fault tolerance in virtualized computer systems use a first guest and a second guest running on virtualization software to produce outputs, which are produced when a workload is executed on the first and second guests. An output of the second guest is compared with an output of the first guest to determine if there is an output match. If there is no output match, the first guest is paused and a resynchronization of the second guest is executed to restore a checkpointed state of the first guest on the second guest. After the resynchronization of the second guest, the paused first guest is caused to resume operation.

Virtual machine fault tolerance

In a computer system running at least a first virtual machine (VM) and a second VM on virtualization software, a computer implemented method for the second VM to provide quasi-lockstep fault tolerance for the first VM includes executing a workload on the first VM and the second VM that involves producing at least one externally visible output and comparing an externally visible output of the second VM with an externally visible output of the first VM to determine if there is an output match. In response to a determination that the externally visible output of the second VM does not match the externally visible output of the first VM, a resynchronization of the second VM is executed. The externally visible output of the first VM is kept from being output externally until completion of the resynchronization.

In a computer system running at least a first virtual machine (VM) and a second VM on virtualization software, a computer implemented method for the second VM to provide quasi-lockstep fault tolerance for the first VM. The method includes enabling operations of the second VM to diverge from being in lockstep with operations with the first VM without resynchronizing the second VM with the first VM, if output of the second VM is not diverging from output of the first VM. The output of the second VM is compared with the output of the first VM to determine whether the output of the second VM has diverged from the output of the first VM. In response to a determination that the output of the second VM has diverged from the output of the first VM, a resynchronization of the second VM is executed.

The invention relates to page fault handling in a virtualized computer system in which at least one guest page table maps virtual addresses to guest physical addresses, some of which are backed by machine addresses, and wherein at least one shadow page table and at least one translation look-aside buffer map the virtual addresses to the corresponding machine addresses. Indicators are maintained in entries of at least one shadow page table, wherein each indicator denotes a state of its associated entry from a group of states consisting of: a first state and a second state. An enhanced virtualization layer processes hardware page faults. States of shadow page table entries corresponding to hardware page faults are determined. Responsive to a shadow page table entry corresponding to a hardware page fault being in the first state, that page fault is delivered to a guest operating system for processing without activating a virtualization software component. On the other hand, responsive to a shadow page table entry corresponding to a hardware page fault being in the second state, that page fault is delivered to a virtualization software component for processing.

Page fault handling in a virtualized computer system

In a computer system running a primary virtual machine (VM) on virtualization software on a primary virtualized computer system (VCS) and running a secondary VM on virtualization software on a secondary VCS, a method for the secondary VM to provide quasi-lockstep fault tolerance for the primary VM includes: as the primary VM is executing a workload, virtualization software in the primary VCS is: (a) causing predetermined events to be recorded in an event log, (b) keeping output associated with the predetermined events pending, and (c) sending the log entries to the virtualization software in the secondary VCS; as the secondary VM is replaying the workload, virtualization software in the secondary VCS is: (a) sending acknowledgements indicating that log entries have been received; (b) when the virtualization software encounters one of the predetermined events, searching the log entries to determine whether a log entry corresponding to the same event was received from the primary VCS, and if so, comparing data associated with the predetermined event produced by the secondary VM with that of the primary VM; if there is a match, the virtualization software in the secondary VCS transmitting an acknowledgement to the virtualization software in the primary VCS; one of the virtualization software in the primary or secondary VCS dropping the event and the other dispatching the output; and if there is no match, performing a checkpoint resynchronization.

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Mountain View, CA, United States of America

Rohit Jain