file xen/include/xen/lib/x86/cpu-policy.h: Meaning of CPUID constants

[Fonyuy-Asheri Caleb <fonyuy-asheri.caleb@xxxxxxxx>]

Hi,

I am currently doing a study on the way xen handles CPUID information.

I came across these constants in the code (xen/include/xen/lib/x86/cpu-policy.h file) but no explanation of why they have been set that way.

#define CPUID_GUEST_NR_BASIC      (0xdu + 1)

#define CPUID_GUEST_NR_CACHE      (5u + 1)

#define CPUID_GUEST_NR_FEAT       (2u + 1)

#define CPUID_GUEST_NR_TOPO       (1u + 1)

#define CPUID_GUEST_NR_XSTATE     (62u + 1)

#define CPUID_GUEST_NR_EXTD_INTEL (0x8u + 1)

#define CPUID_GUEST_NR_EXTD_AMD   (0x21u + 1)

Please can someone explain to me why we have these constants or point to a documentation which explains it? 

I am particularly interested in the CPUID_GUEST_NR_BASIC given that for intel processors for example, we have

basic leaves running up to 0x21u already for recent processors. This value sort of forces a particular max leaf value. 

Caleb