  WarpX is a general purpose electromagnetic particle-in-cell code that was
originally designed to run on many-core CPU architectures. We describe the
strategy followed to allow WarpX to use the GPU-accelerated nodes on OLCF's
Summit supercomputer, a strategy we believe will extend to the upcoming
machines Frontier and Aurora. We summarize the challenges encountered, lessons
learned, and give current performance results on a series of relevant benchmark
problems.
