mm: fix mapping memory in non-present PDEs

src/mm/page_tables.c

@@ -48,11 +48,22 @@ void map_page(void *physaddr, void *virtualaddr, unsigned int flags) {
     // adjust the PDE accordingly.
 
     if (!(pd[pdindex] & 0x1)) { // If PDE not present
-        unsigned long *new_pt = alloc_page();
-        unsigned long *virt_pt = (unsigned long *)(0xC0000000 + new_pt);
-        memset(virt_pt, 0, 4096);
-        //pd[pdindex] = (uint32_t)new_pt | 0x3; // Present, R/W
-        pd[pdindex] = (uint32_t)new_pt | (flags & 0x7); // Add User bit if needed
+        void *new_pt_phys = alloc_page();
+        if (!new_pt_phys) {
+            printf("failed to allocate a new page table\n");
+            return;
+        }
+
+        unsigned int pde_flags = PAGE_PRESENT | PAGE_RW;
+        if (flags & PAGE_USER) {
+            pde_flags |= PAGE_USER;
+        }
+        pd[pdindex] = (unsigned long)new_pt_phys | pde_flags;
+
+        uint32_t *pt_virt = (uint32_t*)(0xFFC00000 + (pdindex << 12));
+        asm volatile("invlpg (%0)" : : "r" (pt_virt) : "memory");
+
+        memset(pt_virt, 0, 4096);
     }
 
     uint32_t *pt = (uint32_t*)(0xFFC00000 + (pdindex << 12));