Local KD -- can't access physical address 0xFFFFFFF0 but you can with RwEverything

I’ve never been able to access 0xf0000000 range using !db on local debug, and I’ve tried !db -m 00000000`fffffff0 and !db [uc] 00000000`fffffff0. I only get Physical memory read at fffffff0 failed. It works fine on RwEverything. Any ideas?