powerpc/32s: Always map kernel text and rodata with BATs

Since commit 2b279c03 ("powerpc/32s: Allow mapping with BATs with
DEBUG_PAGEALLOC"), there is no real situation where mapping without
BATs is required.

In order to simplify memory handling, always map kernel text
and rodata with BATs even when "nobats" kernel parameter is set.

Also fix the 603 TLB miss exceptions that don't require anymore
kernel page table if DEBUG_PAGEALLOC.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/da51f7ec632825a4ce43290a904aad61648408c0.1606285013.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/head_book3s_32.S

@@ -457,13 +457,13 @@ InstructionTLBMiss:
  */
 	/* Get PTE (linux-style) and check access */
 	mfspr	r3,SPRN_IMISS
-#if defined(CONFIG_MODULES) || defined(CONFIG_DEBUG_PAGEALLOC)
+#ifdef CONFIG_MODULES
 	lis	r1, TASK_SIZE@h		/* check if kernel address */
 	cmplw	0,r1,r3
 #endif
 	mfspr	r2, SPRN_SPRG_PGDIR
 	li	r1,_PAGE_PRESENT | _PAGE_ACCESSED | _PAGE_EXEC
-#if defined(CONFIG_MODULES) || defined(CONFIG_DEBUG_PAGEALLOC)
+#ifdef CONFIG_MODULES
 	bgt-	112f
 	lis	r2, (swapper_pg_dir - PAGE_OFFSET)@ha	/* if kernel address, use */
 	addi	r2, r2, (swapper_pg_dir - PAGE_OFFSET)@l	/* kernel page table */

arch/powerpc/mm/book3s32/mmu.c

@@ -157,11 +157,9 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
 	unsigned long done;
 	unsigned long border = (unsigned long)__init_begin - PAGE_OFFSET;
 
-	if (__map_without_bats) {
-		pr_debug("RAM mapped without BATs\n");
-		return base;
-	}
-	if (debug_pagealloc_enabled()) {
+
+	if (debug_pagealloc_enabled() || __map_without_bats) {
+		pr_debug_once("Read-Write memory mapped without BATs\n");
 		if (base >= border)
 			return base;
 		if (top >= border)