Intel 64 and IA-32 Architectures Software Developers Manual Volume 3A, System Programming Guide, Part 1

Vol. 3A 4-3
PROTECTION
• Requested privilege level (RPL) field — (Bits 0 and 1 of any segment
selector.) Specifies the requested privilege level of a segment selector.
• Current privilege level (CPL) field — (Bits 0 and 1 of the CS segment
register.) Indicates the privilege level of the currently executing program or
procedure. The term current privilege level (CPL) refers to the setting of this
field.
• User/supervisor (U/S) flag — (Bit 2 of a page-directory or page-table entry.)
Determines the type of page: user or supervisor.
• Read/write (R/W) flag — (Bit 1 of a page-directory or page-table entry.)
Determines the type of access allowed to a page: read only or read-write.
Figure 4-1 shows the location of the various fields and flags in the data, code, and
system- segment descriptors; Figure 3-6 shows the location of the RPL (or CPL) field
in a segment selector (or the CS register); and Figure 3-14 shows the location of the
U/S and R/W flags in the page-directory and page-table entries.