This is a recently added warning (see https://review.coreboot.org/13949) that tells you that you are trying to use a payload which would overlap the parts of coreboot that are loading it (risking random corruption errors and such). The fix is to link your payload to a different base address which does not overlap the POSTRAM_CBFS_CACHE region in the memlayout.ld of your board/chipset.
Which board are you building for and which payload are you trying to use?