Adding support for refcounted page tables. Fixed freeing of kernel pmds on copy_page_tables

include/l4/generic/tcb.h

@@ -39,6 +39,12 @@ struct task_ids {
 	l4id_t tgid;
 };
 
+/* A simple page table with a reference count */
+struct address_space {
+	struct pgd_table_t *pgd;
+	int ktcb_refs;
+};
+
 struct ktcb {
 	/* User context */
 	task_context_t context;
@@ -86,7 +92,7 @@ struct ktcb {
 	int nlocks;
 
 	/* Page table information */
-	pgd_table_t *pgd;
+	struct address_space *space;
 
 	/* Fields for ipc rendezvous */
 	struct waitqueue_head wqh_recv;

src/api/thread.c

@@ -256,6 +256,12 @@ int thread_setup_new_ids(struct task_ids *ids, unsigned int flags,
 	return 0;
 }
 
+#define KTCB_CREATE_PAGE_TABLES		(1 << 0)
+/* Allocates a ktcb and page tables depending on flags */
+struct ktcb *ktcb_create(unsigned int flags)
+{
+
+}
 /*
  * Creates a thread, with a new thread id, and depending on the flags,
  * either creates a new space, uses the same space as another thread,

src/arch/arm/v5/mm.c

@@ -460,9 +460,11 @@ pgd_table_t *copy_page_tables(pgd_table_t *from)
 	return pgd;
 
 out_error:
-	/* Find all allocated pmds and free them */
+	/* Find all allocated non-kernel pmds and free them */
 	for (int i = 0; i < PGD_ENTRY_TOTAL; i++) {
-		if ((pgd->entry[i] & PGD_TYPE_MASK) == PGD_TYPE_COARSE) {
+		/* Non-kernel pmd that has just been allocated. */
+		if (!is_kern_pgdi(i) &&
+		    (pgd->entry[i] & PGD_TYPE_MASK) == PGD_TYPE_COARSE) {
 			/* Obtain the pmd handle */
 			pmd = (pmd_table_t *)
 			      phys_to_virt((pgd->entry[i] &