Host Virtual Counter Scaling for Cross-Host VM Migration

The patent introduces a virtual counter register and virtual timer registers as intermediary layers between applications and hardware registers. These virtual registers are accessed through paravirtualized functions that apply scaling factors, enabling time scaling while maintaining ease of access for applications. The virtual counter value is derived from the system count through scaling operations without requiring direct hardware register access.

The patent implements scaling factors (multiplicand, addend, shift) that can be dynamically adjusted based on the host environment. When a VM migrates between hosts with different clock frequencies, the paravirtualized functions update these scaling parameters to maintain consistent timing behavior. This allows adaptation to different hardware configurations without fundamentally changing the counter and timer architecture.

The patent segments the timing functionality into distinct layers: hardware counters, virtual counter registers, and paravirtualized access functions. This segmentation allows the virtualization layer to manipulate time through scaling factors without requiring complex changes to the underlying hardware. Each layer has a specific responsibility, simplifying the overall virtualization structure while maintaining adaptability.