/**
* Fills a page of memory with repeating data, used to fill empty tables in
*
* @param page the page number to fill in
* @param data the address of data to fill with
* @param data_size the size of each copt of data stored
*/
void fill_page_with_data(unsigned int page, void * data, unsigned int data_size) {
void * phys;
struct mmu_L1_4k_desc * L1_table;
struct mmu_L2_4k_desc * L2_table;
unsigned int L1_index;
unsigned int L2_index;
unsigned int i;
unsigned int j;
unsigned int entries;
//get physical address of the page
phys = page_number_to_address(page);
//set up a temporary manual mapping into kernel memory
L1_index = get_L1_index((void*)MMU_TEMP_MAP);
L2_index = get_L2_index((void*)MMU_TEMP_MAP);
//get the L1 table and set the entry to map to the L2 base address
L1_table = (struct mmu_L1_4k_desc *)get_page_table_addr();
fill_L1_index(L1_table, L1_index, MMU_L1_COURSE_TYPE, 0, 0, (void*)MMU_TEMP_L2_ADDR);
//get the L2 table and set the entry to map to the physical base address
L2_table = (struct mmu_L2_4k_desc *)(L1_table[L1_index].L2_base_addr << 10);
fill_L2_index(L2_table, L2_index, MMU_L2_SMALL_TYPE, 0, 0, MMU_AP_USER_NONE, phys);
//write the data out to the page
entries = PAGE_SIZE / data_size;
for(i = 0; i < entries; ++i)
for(j = 0; j < data_size; ++j)
((char *)MMU_TEMP_MAP)[data_size*i+j] = ((char *)data)[j];
//remove the manual mapping from the mmu (done here!)
L2_table[L2_index].type = MMU_L2_NOMAP_TYPE; //set L2 entry to nomap
L1_table[L1_index].type = MMU_L1_NOMAP_TYPE; //set L1 entry to nomap
}
// This clears a page table entry by clearing its present bit.
// It is called by the OS (in kernel.c) when a page is evicted
// from a page frame.
void pt_clear_page_table_entry(VPAGE_NUMBER vpage)
{
int L1_index = get_L1_index(vpage);
int L2_index = get_L2_index(vpage);
PT_ENTRY* table_L2 = first_level_page_table[L1_index];
if(table_L2 == NULL) {
/* Control should never reach here */
SAY("Tried to remove a vpage that does not exist!\n");
return;
}
table_L2[L2_index] = 0; //clear the entry
}
// This inserts into the page table an entry mapping of the
// the specified virtual page to the specified page frame.
// It might require the creation of a second-level page table
// to hold the entry, if it doesn't already exist.
void pt_update_pagetable(VPAGE_NUMBER vpage, PAGEFRAME_NUMBER pframe)
{
int L1_index = get_L1_index(vpage);
int L2_index = get_L2_index(vpage);
PT_ENTRY* table_L2 = first_level_page_table[L1_index];
if(table_L2 == NULL) {
table_L2 = create_L2_page_table(L1_index);
}
unsigned int value = pframe | PRESENT_BIT_MASK;
table_L2[L2_index] = value;
}
//This is called when there is a TLB_miss.
// Using the page table, this looks up the page frame
// corresponding to the specified virtual page.
// If the desired page is not present, the variable page_fault
// should be set to TRUE (otherwise FALSE).
PAGEFRAME_NUMBER pt_get_pageframe(VPAGE_NUMBER vpage)
{
int L1_index = get_L1_index(vpage);
int L2_index = get_L2_index(vpage);
PAGEFRAME_NUMBER pf_number = find_pf_number(L1_index,L2_index);
if (pf_number == -1) { //could not be found
page_fault = TRUE;
}
else{
page_fault = FALSE;
return pf_number;
}
}
/**
* Gets the L2 description for a virtual memory address
*
* @param addr the virtual memory address to look up
*
* @return L2 description for the given address
*/
struct mmu_L2_4k_desc * get_L2_desc(void * addr) {
struct mmu_L2_4k_desc * table;
struct mmu_L1_4k_desc * entry;
//get the L1 entry
entry = get_L1_desc(addr);
//if the L1 entry is no mapping, return SYSERR
if(entry->type == MMU_L1_NOMAP_TYPE)
return (void *)SYSERR;
//get the page table address
table = (struct mmu_L2_4k_desc *)((void *)(entry->L2_base_addr << 10));
//return the single L2 description
return &(table[get_L2_index(addr)]);
}
