ACCELERATED VIRTUAL PASSTHROUGH I/O DEVICE PERFORMANCE

An L2 virtual machine (VM) operating in a trust domain invokes a memory operation involving a virtual I/O device passed through from an L1 VM. Invocation of the memory operation causes an L2 virtual I/O device driver to make a hypercall to a trust domain management module. The hypercall comprises a memory-mapped I/O (MMIO) address of the virtual I/O device as seen by the L2 VM (L2 MMIO address), which matches the MMIO address of the virtual I/O device as seen by the L1 VM. The module passes hypercall information to an LO hypervisor, which forwards the information to an emulator operating in LO user space that emulates the back end of the virtual I/O device operating on the L1 VM. The emulator determines an emulated software response based on the L2 MMIO address and the memory operation is carried out.