Intel IA-32 manual

4-44 Vol. 3A
PROTECTION
Table 4-10. Reserved Bit Checking WIth Execute-Disable Bit Capability Not Enabled
4.13.4 Exception Handling
When execute disable bit capability is enabled (IA32_EFER.NXE = 1), conditions for a page
fault to occur include the same conditions that apply to an IA-32 processor without execute
disable bit capability plus the following new condition: an instruction fetch to a linear address
that translates to physical address in a memory page that has the execute-disable bit set.
An Execute Disable Bit page fault can occur at all privilege levels. It can occur on any instruc-
tion fetch, including (but not limited to): near branches, far branches, CALL/RET/INT/IRET
execution, sequential instruction fetches, and task switches. The execute-disable bit in the page
translation mechanism is checked only when:
•IA32_EFER.NXE = 1.
•The instruction translation look-aside buffer (ITLB) is loaded with a page that is not
already present in the ITLB.
Mode Paging Mode Check Bits
32-bit KByte paging (non-PAE) No reserved bits checked
PSE36 - PDE, 4-MByte page Bit [21]
PSE36 - PDE, 4-KByte page No reserved bits checked
PSE36 - PTE No r eserved bits checked
PAE - PDP table entry Bits [63:40] & [8:5] & [2:1]1
PAE - PDE, 2-MByte page Bits [63:40] & [20:13]1
PAE - PDE, 4-KByte page Bits [63:40]1
PAE - PTE Bits [63:40]1
64-bit PML4E Bit [63], bits [51:40]
PDPTE Bit [63], bits [51:40]
PDE, 2-MByte page Bit [63], bits [51:40] & [20:13]
PDE, 4-KByte page Bit [63], bits [51:40]
PTE Bit [63], bits [51:40]
NOTES:
1. Reserved bit checking also applies to bits 39:36 for processors that support only 36-bits of physical
address. For processor that support only 32 bits of physical address, reserved bit checking also applies
to bits 39:32.