Question regarding usage of memcpyDtoH for device to device copy

[ChayootO]

I have downloaded PhysX5 repo and ran the snippet “SnippetPBF” in order to get a notion of how to render particles position calculated by PhysX5 (with cuda) without retrieving the particles position from the gpu to the cpu first and encountered the following code (note that USE_CUDA_INTEROP is defined and I have copied only what I believe to be the relevant parts of the functions ):

PxParticleAndDiffuseBuffer* userBuffer = getParticleBuffer();
PxVec4* positions = userBuffer->getPositionInvMasses();
PxCudaContextManager* cudaContextManager = scene->getCudaContextManager();
cudaContextManager->acquireContext();
PxCudaContext* cudaContext = cudaContextManager->getCudaContext();
cudaContext->memcpyDtoH(sPosBuffer.map(), CUdeviceptr(positions), sizeof(PxVec4) * numParticles);
cudaContextManager->releaseContext();

If we take a look at:

void* SharedGLBuffer::map()
{
if (devicePointer)
    return devicePointer;
size_t numBytes;
cudaContextManager->acquireContext();
devicePointer = mapCudaGraphicsResource(reinterpret_cast<CUgraphicsResource*>(&vbo_res), numBytes, 0);
cudaContextManager->releaseContext();
return devicePointer;
}

and then at:

void* mapCudaGraphicsResource(CUgraphicsResource* vbo_resource, size_t& numBytes, CUstream stream = 0)
{
CUresult result0 = cuGraphicsMapResources(1, vbo_resource, stream);
PX_UNUSED(result0);
void* dptr;
CUresult result1 = cuGraphicsResourceGetMappedPointer((CUdeviceptr*)&dptr, &numBytes, *vbo_resource);
PX_UNUSED(result1);
return dptr;
}

It seems that sPosBuffer.map() returns a pointer to a device address and not a cpu address. If so why is the function used is memcpyDtoH and not memcpyDtoD and why does it work?