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// MMU recursive mapping (-512GB ~ -256GB)
// ----------------------------------------------
#define MMU_RECURSIVE_SLOT      (510UL)


// Convert an address into array index of a structure
// E.G. int index = MMU_PML4_INDEX(0xFFFFFFFFFFFFFFFF); // index = 511
#define MMU_PML4_INDEX(addr)    ((((uintptr_t)(addr))>>39) & 511)
#define MMU_PDPT_INDEX(addr)    ((((uintptr_t)(addr))>>30) & 511)
#define MMU_PD_INDEX(addr)      ((((uintptr_t)(addr))>>21) & 511)
#define MMU_PT_INDEX(addr)      ((((uintptr_t)(addr))>>12) & 511)

// Base address for paging structures
#define KADDR_MMU_PT            (0xFFFF000000000000UL + (MMU_RECURSIVE_SLOT<<39))
#define KADDR_MMU_PD            (KADDR_MMU_PT         + (MMU_RECURSIVE_SLOT<<30))
#define KADDR_MMU_PDPT          (KADDR_MMU_PD         + (MMU_RECURSIVE_SLOT<<21))
#define KADDR_MMU_PML4          (KADDR_MMU_PDPT       + (MMU_RECURSIVE_SLOT<<12))

// Structures for given address, for example
// uint64_t* pt = MMU_PT(addr)
// uint64_t physical_addr = pt[MMU_PT_INDEX(addr)];
#define MMU_PML4(addr)          ((uint64_t*)  KADDR_MMU_PML4 )
#define MMU_PDPT(addr)          ((uint64_t*)( KADDR_MMU_PDPT + (((addr)>>27) & 0x00001FF000) ))
#define MMU_PD(addr)            ((uint64_t*)( KADDR_MMU_PD   + (((addr)>>18) & 0x003FFFF000) ))
#define MMU_PT(addr)            ((uint64_t*)( KADDR_MMU_PT   + (((addr)>>9)  & 0x7FFFFFF000) ))

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// For initializing, just add
    // Install recursive page directory
    k_PML4[MMU_RECURSIVE_SLOT] = KADDR_PMA(k_PML4) +3;

For cloning page directory when creating new process:
// -------------------------------------------------
MMU_PADDR MMU_clonepagedir(void) {
    uint64_t* clone = (uint64_t*)KADDR_CLONEPD;
    MMU_PADDR paddr = MMU_alloc();
    if ( paddr == 0 ) return 0;
    MMU_mmap ( clone, paddr, 4096, MMU_MMAP_MAPPHY );
    memset ( clone, 0, 256*8 );
    memcpy ( &clone[256], &k_PML4[256], 256*8 );

    // Recursive
    clone[MMU_RECURSIVE_SLOT] = paddr +3;

    MMU_munmap ( clone, 4096, MMU_MUNMAP_NORELEASE );
    return paddr;
}

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0xfffffffffffff000 - PML4
0xffffffffffe00000 - PDPs
0xffffffffc0000000 - page directories
0xffffff8000000000 - page tables