Vol. 3A 4-17
PAGING
Table 4-10. Format of a PAE Page-Directory Entry that References a Page Table
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to reference a page table
1 (R/W)
Read/write; if 0, writes may not be allowed to the 2-MByte region controlled by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 2-MByte region controlled by this entry (see
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the page table referenced by this
entry (see Section 4.9)
5 (A)
Accessed; indicates whether this entry has been used for linear-address translation (see Section 4.8)
6
Ignored
7 (PS)
Page size; must be 0 (otherwise, this entry maps a 2-MByte page; see Table 4-9)
11:8
Ignored
(M–1):12
Physical address of 4-KByte aligned page table referenced by this entry
62:M
Reserved (must be 0)
63 (XD)
If IA32_EFER.NXE = 1, execute-disable (if 1, instruction fetches are not allowed from the 2-MByte region controlled
by this entry; see Section 4.6); otherwise, reserved (must be 0)
Table 4-11. Format of a PAE Page-Table Entry that Maps a 4-KByte Page
Bit
Position(s)
Contents
0 (P)
Present; must be 1 to map a 4-KByte page
1 (R/W)
Read/write; if 0, writes may not be allowed to the 4-KByte page referenced by this entry (see Section 4.6)
2 (U/S)
User/supervisor; if 0, user-mode accesses are not allowed to the 4-KByte page referenced by this entry (see Section
3 (PWT)
Page-level write-through; indirectly determines the memory type used to access the 4-KByte page referenced by
this entry (see Section 4.9)
4 (PCD)
Page-level cache disable; indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9)
5 (A)
Accessed; indicates whether software has accessed the 4-KByte page referenced by this entry (see Section 4.8)
6 (D)
Dirty; indicates whether software has written to the 4-KByte page referenced by this entry (see Section 4.8)
7 (PAT)
If the PAT is supported, indirectly determines the memory type used to access the 4-KByte page referenced by this
entry (see Section 4.9.2); otherwise, reserved (must be 0)
1
8 (G)
Global; if CR4.PGE = 1, determines whether the translation is global (see Section 4.10); ignored otherwise