m68k: mm: Fully initialize the page-table allocator

Also iterate the PMD tables to populate the PTE table allocator. This
also fully replaces the previous zero_pgtable hack.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Will Deacon <will@kernel.org>
Acked-by: Greg Ungerer <gerg@linux-m68k.org>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Tested-by: Greg Ungerer <gerg@linux-m68k.org>
Link: https://lore.kernel.org/r/20200131125403.938797587@infradead.orgSigned-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/mm/init.c

@@ -120,7 +120,7 @@ void free_initmem(void)
 static inline void init_pointer_tables(void)
 {
 #if defined(CONFIG_MMU) && !defined(CONFIG_SUN3) && !defined(CONFIG_COLDFIRE)
-	int i;
+	int i, j;
 
 	/* insert pointer tables allocated so far into the tablelist */
 	init_pointer_table(kernel_pg_dir, TABLE_PGD);
@@ -133,6 +133,17 @@ static inline void init_pointer_tables(void)
 
 		pmd_dir = (pmd_t *)pgd_page_vaddr(kernel_pg_dir[i]);
 		init_pointer_table(pmd_dir, TABLE_PMD);
+
+		for (j = 0; j < PTRS_PER_PMD; j++) {
+			pmd_t *pmd = &pmd_dir[j];
+			pte_t *pte_dir;
+
+			if (!pmd_present(*pmd))
+				continue;
+
+			pte_dir = (pte_t *)__pmd_page(*pmd);
+			init_pointer_table(pte_dir, TABLE_PTE);
+		}
 	}
 #endif
 }