os-k/kaleid/kernel/mm/paging.c

#include <kernel.h>

#define PAGESIZE (4 * KB)
#define PAGEALIGNED __attribute__((__aligned__(4096)))

// Page directory pointer offset
typedef uint    pdpe_t;

// Page directory offset
typedef uint    pde_t;

// Page table entry
typedef uint    pte_t;

// paging.asm
void MmLoadPML4(void *);
void MmEnableWriteProtect(void);
void MmDisableWriteProtect(void);

enum
{
    MF_PRESENT      = 1 << 0,
    MF_READWRITE    = 1 << 1,
    MF_USERMODE     = 1 << 2,
    MF_WRITETHR     = 1 << 3,
    MF_CACHEDIS     = 1 << 4,
    MF_ACCESSED     = 1 << 5,
    MF_DIRTY        = 1 << 6
};

//-----------

pdpe_t pml4[1024] ;

// First PDPE of our pml4
pde_t first_pdpe[1024] PAGEALIGNED;

// First PDP of first_pdpe
pte_t first_pde[1024] PAGEALIGNED;

// First PTE of first_pde
uint first_pte[1024] PAGEALIGNED;

void MmInitPaging(void)
{
    size_t i;

    // Set all PDPEs to kernel-mode not present
    for (i = 0; i < 1024; i++) pml4[i] = MF_READWRITE;
    for (i = 0; i < 1024; i++) first_pdpe[i] = MF_READWRITE;
    for (i = 0; i < 1024; i++) first_pde[i] = MF_READWRITE;
    
    // Set all pages in first_pte to kernel-mode present
    for (i = 0; i < 1024; i++) {
        first_pte[i] = (i * PAGESIZE) | (MF_READWRITE | MF_PRESENT);
    }
    
    // Install the first PTE
    first_pde[0] = (uint)(ulong)first_pte | (MF_READWRITE | MF_PRESENT);
    first_pdpe[0] = (uint)(ulong)first_pde | (MF_READWRITE | MF_PRESENT);
    pml4[0] =  (uint)(ulong)first_pdpe | (MF_READWRITE | MF_PRESENT);

    MmLoadPML4(pml4);
}