struct MMPTE_SUBSECTION

typedef struct _MMPTE_SUBSECTION
{
     ULONG Valid: 1;
     ULONG Unused0: 4;
     ULONG Protection: 5;
     ULONG Prototype: 1;
     ULONG Unused1: 21;
     ULONG SubsectionAddress: 32;
} MMPTE_SUBSECTION, *PMMPTE_SUBSECTION;

Windows Vista Kernel Structures