valid address space ?

I am trying to dump some kernel data structure (walk e.g. task or file data structure on x86_64 arch). Sometime accessing through a pointer, pointer may not be NULL, but pointing to invalid address due to garbage value. What I am looking for is range of address which are valid for kernel data structure. Is it correct to say following address are valid ? - Bit 0 - 47 are considered - Between FFFF8000'00000000 through FFFFFFFF'FFFFFFFF