Specifications

2-22
LOCAL X2APIC ARCHITECTURE
The lowest level number is zero. Level number = 0 is reserved to specify SMT-related
topology information (see Hyper-Threading Technology in Section 7.8 of “Intel® 64
and IA-32 Architectures Software Developer’s Manual“, Vol. 3A). If SMT is not
present in a processor implementation but CPUID leaf 0BH is supported,
CPUID.EAX=0BH, ECX=0 will return EAX = 0, EBX = 1 and level type = 1. Number of
logical processors at the core level is reported at level type = 2.
CPUID.0BH leaf can report “level type“ and “level number“ in any order. Each level
type defines a specific topology configuration within the physical package. Thus there
is no level type corresponding to “package“ for CPUID.0BH leaf. The Level Type
encodings indicate the topology level and need not correspond to any Level number
except level number 0 is reserved for level type SMT.
The legacy processor topology enumeration fields in CPUID.01H and CPUID.04H will
continue to report correct topology up to the maximum values supported by the
fields and 8-bit initial APIC ID. For future processors with topology that exceeds the
limits of CPUID.01H:EBX[23:16],CPUID.01H:EBX[31:24], CPUID.EAX=04H,
ECX=0H:EAX[31:26], these legacy fields will report the respective modulo maximum
values.
If CPUID.0BH returns EBX=0 when input ECX=0 then assume that CPUID.0BH leaf
data for extended processor topology enumeration is not supported on this
processor. Use CPUID.01H and CPUID.04H leaves for topology information.
NOTES:
* Software should use this field (EAX[4:0]) to enumerate processor
topology of the system.
** Software must not use EBX[15:0] to enumerate processor topology
of the system. This value in this field (EBX[15:0]) is only intended for
display/diagnostic purposes. The actual number of logical processors
available to BIOS/OS/Applications may be different from the value of
EBX[15:0], depending on software and platform hardware configura-
tions.
***The value of Level Type field is not related to level numbers in any
way, higher level type values do not mean higher levels. Level Type
field has the following encoding:
0 = Invalid
1 = SMT
2 = Core
3-255 = Reserved
Table 2-4. CPUID Leaf 0BH Information (Contd.)
Initial EAX
Value Information Provided about the Processor