Abstract: A method of data communication between a first virtual machine and a second virtual machine is disclosed. The second virtual machine is executing in a record/replay mode. The method includes copying data from the first virtual machine to a first queue. The first queue is configured to receive the data from the first virtual machine. The first queue has a first queue header section and a first queue data section. The first queue header being write protected and configured to store a tail pointer of the data in the first queue. The tail pointer is updated in the first header section. This update of the tail pointer causes a page fault. The method further includes handling page fault through a page fault handler. The handling includes copying the data from the first queue to a second queue. The second queue being configured to receive a copy of the data and to allow the second virtual machine to access the copy of the data.

Abstract: A method for precisely counting guest branch instructions in a virtualized computer system is described. In one embodiment, guest instructions execute in a direct execution mode of the virtualized computer system. The direct execution mode operates at a first privilege level having a lower privilege than a second privilege level. A branch count of previously executed first privilege level branch instructions is maintained as instructions execute. Execution of a first privilege level branch instruction caused by a control transfer to the direct execution mode is detected. Responsive to the detection, a guest branch instruction count is determined based on the first privilege level branch count.