+/* Populates the base page directory and page table with the
+ kernel virtual mapping, and then sets up the CPU to use the
+ new page directory. Points base_page_dir to the page
+ directory it creates.
+
+ At the time this function is called, the active page table
+ (set up by loader.S) only maps the first 4 MB of RAM, so we
+ should not try to use extravagant amounts of memory.
+ Fortunately, there is no need to do so. */
+static void
+paging_init (void)
+{
+ uint32_t *pd, *pt;
+ size_t page;
+
+ pd = base_page_dir = palloc_get_page (PAL_ASSERT | PAL_ZERO);
+ pt = NULL;
+ for (page = 0; page < ram_pages; page++)
+ {
+ uintptr_t paddr = page * PGSIZE;
+ void *vaddr = ptov (paddr);
+ size_t pde_idx = pd_no (vaddr);
+ size_t pte_idx = pt_no (vaddr);
+
+ if (pd[pde_idx] == 0)
+ {
+ pt = palloc_get_page (PAL_ASSERT | PAL_ZERO);
+ pd[pde_idx] = pde_create (pt);
+ }
+
+ pt[pte_idx] = pte_create_kernel (vaddr, true);
+ }
+
+ /* Store the physical address of the page directory into CR3
+ aka PDBR (page directory base register). This activates our
+ new page tables immediately. See [IA32-v2a] "MOV--Move
+ to/from Control Registers" and [IA32-v3] 3.7.5. */
+ asm volatile ("mov %%cr3, %0" :: "r" (vtop (base_page_dir)));
+}
+