hyperlight_surrogate.exe is a tiny Rust application we use to create multiple virtual machine (VM) partitions per process when running on Windows with the Windows Hypervisor Platform (WHP, e-g Hyper-V). This binary has no functionality. Its purpose is to provide a running process into which memory will be mapped via the WHvMapGpaRange2 Windows API. Hyperlight does this memory mapping to pass parameters into, and fetch return values out of, a given VM partition.
Note: The use of surrogates is a temporary workaround on Windows until WHP allows us to create more than one partition per running process.
These surrogate processes are managed by the host via the surrogate_process_manager which will launch several of these surrogates (up to the 512), assign memory to them, then launch partitions from there, and reuse them as necessary.
hyperlight_surrogate.exe gets built during hyperlight-host's build script, gets embedded into the hyperlight-host Rust library via rust-embed, and is extracted at runtime next to the executable when the surrogate process manager is initialized.