In sys/arch/x86/x86/genfb_machdep.c at line 161, I found the following code:
err = _x86_memio_map(t, (bus_addr_t)fbinfo->physaddr,
fbinfo->width * fbinfo->stride,
BUS_SPACE_MAP_LINEAR | BUS_SPACE_MAP_PREFETCHABLE, &h);
which looks to me like a typo, fbinfo->width should probably be replaced by
fbinfo->height, to map exactly the visible portion of the framebuffer.
