Figure 4-1: Levels of Privilege
System x: The System x servers are powered by Intel processors. Intel processors provide four execution modes, identified with processor privilege levels 0 through 3. The highest privilege level execution mode corresponds to processor privilege level 0; the lowest privilege level execution mode corresponds to processor privilege level 3. The SLES kernel, as with most other
System p: The System p servers are powered by PowerPC, POWER5 and POWER5+ processors. These processors provide three execution modes, identified by the PR bit (bit 49) and the HV bit (bit 3) of the Machine State Register of the processor. Values of 0 for both PR and HV bits indicate a hypervisor execution mode. An HV bit value of 1, and a PR bit value of 0, indicate a supervisor, or kernel, execution mode. An HV bit value of 1 and a PR bit value of 1 indicate a user execution mode.
System z: The System z systems also provide two execution modes identified by the Problem State bit (bit
15)of the processor’s Program Status Word (PSW). A value of 0 indicates a supervisor, or kernel, execution mode, and the value of 1 indicates a problem state, or user, execution mode.
eServer 326: The eServer 326 servers are powered by AMD Opteron processors. These processors provide four execution modes identified with processor privilege levels 0 through 3. The highest privilege level execution mode corresponds to processor privilege level 0; the lowest privilege level execution mode corresponds to processor privilege level 3. The SLES kernel, as with most other
User and kernel modes, which are offered by all of the eServer systems, implement hardware privilege as follows:
•When the processor is in kernel mode, the program has hardware privilege because it can access and modify any addressable resources, such as memory, page tables, I/O address space, and memory management registers. This is not possible in the user mode.
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