kernel/vmm.h

/*
 * ELSA OS - Virtual Memory Manager Header
 * Temporal Epistemic Separation Kernel v0.4
 * 2026-05-16
 */

#ifndef ELSA_VMM_H
#define ELSA_VMM_H

#include <stdint.h>
#include <stddef.h>
#include <stdbool.h>

/* ============================================================
 * PAGE CONSTANTS
 * ============================================================ */

#define PAGE_SIZE           0x1000ULL       /* 4KB */
#define PAGE_SIZE_2MB       0x200000ULL     /* 2MB */
#define PAGE_SIZE_1GB       0x40000000ULL   /* 1GB */

#define PAGE_FLAG_PRESENT   0x001ULL
#define PAGE_FLAG_WRITE     0x002ULL
#define PAGE_FLAG_USER      0x004ULL
#define PAGE_FLAG_HUGE      0x080ULL
#define PAGE_FLAG_GLOBAL    0x100ULL
#define PAGE_FLAG_NX        (1ULL << 63)

#define PAGE_ADDR_MASK      0x000FFFFFFFFFF000ULL
#define PAGE_ADDR_MASK_2MB  0x000FFFFFFFE00000ULL

#define HIGHER_HALF_BASE    0xFFFF800000000000ULL
#define USER_SPACE_BASE     0x0000000000000000ULL
#define USER_SPACE_SIZE     0x0000800000000000ULL  /* 128TB user space */

/* ============================================================
 * PAGE TABLE STRUCTURES (x86_64 4-level paging)
 * ============================================================ */

typedef struct {
    uint64_t entries[512];
} kernel_pt_t;

typedef struct {
    uint64_t entries[512];
} kernel_pd_t;

typedef struct {
    uint64_t entries[512];
} kernel_pdp_t;

typedef struct {
    uint64_t entries[512];
} kernel_page_table_t;

/* ============================================================
 * ADDRESS SPACE
 * ============================================================ */

typedef int pid_t;

typedef struct {
    kernel_page_table_t *pml4;
    uintptr_t base_virt;
    size_t size;
    pid_t pid;
    int refcount;
} address_space_t;

/* ============================================================
 * BITMAP
 * ============================================================ */

typedef struct {
    uint8_t *bits;
    size_t num_bits;
} bitmap_t;

/* ============================================================
 * VMM API
 * ============================================================ */

/* Initialization */
int vmm_init(uintptr_t phys_mem_start, size_t phys_mem_size,
             uintptr_t kernel_virt_base);

/* Page mapping */
int vmm_map_page(kernel_page_table_t *pml4, uintptr_t virt,
                 uintptr_t phys, uint64_t flags);
int vmm_unmap_page(kernel_page_table_t *pml4, uintptr_t virt);

/* Address space management */
address_space_t *vmm_create_address_space(void);
int vmm_switch_address_space(address_space_t *as);
void vmm_destroy_address_space(address_space_t *as);

/* Copy-on-write */
int vmm_copy_on_write(address_space_t *src, address_space_t *dst,
                      uintptr_t virt, size_t size);

/* Page fault handler */
void vmm_page_fault_handler(uintptr_t fault_addr, uint64_t error_code);

/* Kernel allocator */
void *vmm_kernel_alloc(size_t size);
void vmm_kernel_free(void *ptr, size_t size);

#endif /* ELSA_VMM_H */