It's something common to all modern GPUs, not just NVIDIA: most of the logic is in a user space library loaded by the OpenGL or Vulkan loader into each program. That library writes a stream of commands into a buffer (plus all the necessary data) directly into memory accessible to the GPU, and there's a single system call at the end to ask the operating system kernel to tell the GPU to start reading from that command buffer. That is, other than memory allocation and a few other privileged operations, the user space programs talk directly to the GPU.