Linux has supported KVM virtualization with RISC-V for several years while now patches are pending to introduce Xen hypervisor support for this CPU architecture for RISC-V guests.
The Serbian software consulting firm RT-RK has been working on patches for allowing RISC-V to run as a Xen guest. The Xen hypervisor continues to prove popular in some areas such as for automotive and some safety critical applications.
Around 800 lines of new Linux kernel code allow for running RISC-V as a Xen guest by adding various Xen-specific hypercalls and interfaces. But right now this code just stubs out the implementations for memory management and some other features without completing all of the integration work at this time.
In any event for those interested in the prospects of RISC-V guests with Xen can see this Linux kernel mailing list thread for the initial code working on this support.