Which instructions can not be issued in specific CPU ring

Question

According to this source (Level 3 - 5) specific CPU rings can not do certain things, such as ring 1, 2, 3 code can not set up GDT, as os kernel would crash.

While i

Answer 1

The following instructions cannot be executed in Ring 3:

LGDT
LLDT
LTR
LIDT
MOV (to and from control registers only)
MOV (to and from debug registers only)
LMSW
CLTS
INVD
WBINVD
INVLPG
HLT
RDMSR
WRMSR
RDPMC
RDTSC