Q: Is it possible to directly connect a Hyper-V virtual machine to an InfiniBand connection?
A: No. Hyper-V virtual machines (VMs) need to connect to networking via a virtual switch or through Single-Root Input/Output (I/O) Virtualization (SR-IOV). Leveraging InfiniBand connectivity typically means using Remote Direct Memory Access (RDMA), which currently isn't supported via a virtual switch and therefore isn't available to VMs. The only currently supported use of InfiniBand is RDMA over InfiniBand for SMB traffic and user-mode RDMA over InfiniBand for HPC communications. Outside of these two scenarios, there is no InfiniBand support—which means no support for VMs.
Several people mail have me about this, so I did some digging as to the reason. It seems that some network infrastructure vendors are heavily pushing their InfiniBand solutions and claiming to support Hyper-V over InfiniBand, even though Microsoft doesn't support it. In this scenario the IP over InfiniBand (IPoIB) miniport device is used by a Hyper-V virtual switch, to which VMs then connect. However, some organizations I work with have tried this method and have reported problems.
It's important to remember that RDMA wouldn't be exposed to the VMs via the virtual switch with this method, nor does this approach use SR-IOV to directly map VMs to the InfiniBand card. The only benefit at this point is a very fast connection, which Windows Server 2012 R2 would be able to take advantage of using its virtual Receive Side Scaling (vRSS) feature. But until Microsoft tests and supports this approach, I would be very hesitant to use it.