VTdVi

VTdVi is a hypothetical standard in computer virtualization that envisions an extension of Intel VT-d (Virtualization Technology for Directed I/O) to include a bidirectional virtualization interface (Vi) for I/O devices. The concept aims to enable more flexible and efficient communication between host and guest environments while preserving strong isolation guarantees.

Concept and scope

VTdVi would extend the IOMMU with bidirectional channels, allowing not only guest-initiated DMA but also controlled host-to-guest signaling and event delivery. It defines a policy language and interfaces for allocating I/O resources, securing device pass-through, and managing interrupt routing in multi-tenant or multi-VM configurations. The goal is to reduce reliance on emulation and to support more complex I/O topologies without sacrificing containment.

Hardware and software requirements

A VTdVi deployment, in this concept, requires IOMMU hardware or firmware capable of advanced remapping and bidirectional communication, PCIe device pass-through support, and tight integration with hypervisors and device drivers. Compatibility would depend on extensions in both firmware and virtualization platforms to interpret the Vi channels and policy definitions.

Architecture and operation

In a VTdVi model, the IOMMU handles remapping for direct device access, while VM agents and the hypervisor coordinate resource allocation, policy enforcement, and event delivery. Device drivers would be capable of operating with remapped addresses and special communication channels, enabling more efficient I/O orchestration across guests and the host.

Status

As of this article, VTdVi remains a hypothetical concept or research proposal with limited or no formal production deployments. It appears primarily in theoretical discussions and prototype studies rather than formal standards. Related topics include VT-d, IOMMU, PCI passthrough, and SR-IOV.