Power ISA/Privilege States

• ultravisor privileged state
• hypervisor privileged state
• privileged state / supervisor mode
• problem state / user mode

At the moment very little information exists about the ultravisor state. It is not mentioned in Power ISA version 2.07 documents at all, and version 3.0B only mentions it as a possible classification for instructions:

Privilege Classification of Instructions in Power ISA

Code	2.07	3.0B	Description
P	Yes	Yes	a privileged instruction.
O	Yes	Yes	an instruction that is treated as privileged or nonprivileged (or hypervisor, for mtspr), depend- ing on the SPR or PMR number.
PI	No	Yes	an instruction that is illegal in privileged state.
H	Yes	Yes	an instruction that can be executed only in hypervisor state
PH	Yes	No	a hypervisor privileged instruction if Category Embedded.Hypervisor is implemented; otherwise denotes a privileged instruction.
M	Yes	No	an instruction that is treated as privileged or nonprivileged, depending on the value of the UCLE bit in the MSR
U	No	Yes	an instruction that can be executed only in ultravisor state