In the course of their accretion phase, massive (proto)stars impact their natal environment in a variety of feedback effects such as thermal heating, protostellar outflows, radiative forces, and ionization. Here, I overview our most recent simulation results in terms of mass loss of the stellar environment and the stellar as well as disk accretion efficiency. Our most up-to-date simulations include all of the feedback effects mentioned above and allow us to shed light on the physical reason for the upper mass limit of present-day stars.