Intel 64 and IA-32 Architectures Software Developers Manual Volume 3B, System Programming Guide Part 2

Table Of Contents
Vol. 3 25-7
SYSTEM MANAGEMENT
The following registers are saved (but not readable) and restored upon exiting SMM:
Control register CR4. (This register is cleared to all 0s while in SMM).
The hidden segment descriptor information stored in segment registers CS, DS,
ES, FS, GS, and SS.
7FDCH EBX Yes
7FD8H EDX Yes
7FD4H ECX Yes
7FD0H EAX Yes
7FCCH DR6 No
7FC8H DR7 No
7FC4H TR
1
No
7FC0H Reserved No
7FBCH GS
1
No
7FB8H FS
1
No
7FB4H DS
1
No
7FB0H SS
1
No
7FACH CS
1
No
7FA8H ES
1
No
7FA4H I/O State Field, see Section 25.7 No
7FA0H I/O Memory Address Field, see Section 25.7 No
7F9FH-7F03H Reserved No
7F02H Auto HALT Restart Field (Word) Yes
7F00H I/O Instruction Restart Field (Word) Yes
7EFCH SMM Revision Identifier Field (Doubleword) No
7EF8H SMBASE Field (Doubleword) Yes
7EF7H - 7E00H Reserved No
NOTE:
1. The two most significant bytes are reserved.
Table 25-1. SMRAM State Save Map (Contd.)
Offset
(Added to SMBASE +
8000H)
Register Writable?