/*
 * @author  xamidev <xamidev@riseup.net>
 * @brief   Virtual memory manager
 * @license GPL-3.0-only
 */

/*
The VMM (virtual memory manager) will have two roles:
- mapping pages
- unmapping pages
in a specified virtual space

compared to the PMM which allocs/frees 4kb frames ("physical pages").
*/

#include "vmm.h"
#include "paging.h"
#include <stddef.h>
#include "pmm.h"
#include <kernel.h>

void* vmm_pt_root = 0;

// Linked list head for virtual memory objects
struct vm_object* vm_objs = NULL;


uint64_t convert_x86_vm_flags(size_t flags)
{
    uint64_t value = 0;
    if (flags & VM_FLAG_WRITE)
    {
        value |= PTE_WRITABLE;
    }
    if (flags & VM_FLAG_USER)
    {
        value |= PTE_USER;
    }
    if ((flags & VM_FLAG_EXEC) == 0)
    {
        value |= PTE_NOEXEC;
    }
    return value;
}

extern uint64_t *kernel_pml4;

void vmm_setup_pt_root()
{
    // We alloc a physical page (frame) for the pointer, then map it
    // to virt (pointer)
    uintptr_t phys = pmm_alloc();
    vmm_pt_root = (void*)kernel_pml4;
    paging_map_page(kernel_pml4, (uint64_t)vmm_pt_root, phys, convert_x86_vm_flags(VM_FLAG_WRITE | VM_FLAG_EXEC));
    DEBUG("VMM setup: vmm_pt_root=0x%p (phys=0x%p)", vmm_pt_root, phys);
}

/* void* vmm_alloc(size_t length, size_t flags)
{
    // We will try to allocate at least length bytes, which have to be rounded UP to
    // the next page so its coherent with the PMM
    size_t len = ALIGN_UP(length, PAGE_SIZE);

    // Need to implement this (as linked list)
    // but for now kernel heap is sufficient
    // The VMM will prob be more useful when we have userspace
} */

void vmm_init()
{
    vmm_setup_pt_root();
}