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 5.1. Privileged-Mode Organization

 The facilities described in the privileged-mode environment are classified as either privilege 1 or privilege 2. These designations relate to a suggested hierarchy of privileged access. The access hierarchy is defined to support a 2-level operating environment. An example of such an operating environment is when multiple operating systems run concurrently on top of a more privileged hypervisor. This type of operating environment implements logical partitioning.

 Privilege 1 registers are the most privileged. They are intended to be accessed by a hypervisor or by firmware operating in hypervisor mode[2] (HV = '1' and PR = '0') when supporting logical partitioning. Privilege 2 registers are intended for privileged operating-system code running in the HV = '0' and PR = '0' mode. When a single-level operating environment exists, firmware and the privileged operating system typically combine privilege 1 and privilege 2 resources into one privileged level.

 The page table must be set up so that only privileged mode software can access the facilities in the privileged-mode environment. Problem-state software must never be allowed access to any facilities that are defined in the privileged-mode environment. The PSL does not check that an access to a privileged-mode facility is performed by a privileged-mode process. This authorization checking is provided by the host processor's page protection mechanism.

[2] For information about hypervisor mode, see the Power ISA.

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