powerpc/32s: Allow mapping with BATs with DEBUG_PAGEALLOC

DEBUG_PAGEALLOC only manages RW data.

Text and RO data can still be mapped with BATs.

In order to map with BATs, also enforce data alignment. Set
by default to 256M which is a good compromise for keeping
enough BATs for also KASAN and IMMR.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/fd29c1718ee44d82115d0e835ced808eb4ccbf51.1589866984.git.christophe.leroy@csgroup.eu

arch/powerpc/Kconfig

@@ -797,6 +797,7 @@ config DATA_SHIFT
 	range 17 28 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC) && PPC_BOOK3S_32
 	range 19 23 if (STRICT_KERNEL_RWX || DEBUG_PAGEALLOC) && PPC_8xx
 	default 22 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
+	default 18 if DEBUG_PAGEALLOC && PPC_BOOK3S_32
 	default 23 if STRICT_KERNEL_RWX && PPC_8xx
 	default 23 if DEBUG_PAGEALLOC && PPC_8xx && PIN_TLB_DATA
 	default 19 if DEBUG_PAGEALLOC && PPC_8xx

arch/powerpc/mm/book3s32/mmu.c

@@ -170,6 +170,12 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
 		pr_debug("RAM mapped without BATs\n");
 		return base;
 	}
+	if (debug_pagealloc_enabled()) {
+		if (base >= border)
+			return base;
+		if (top >= border)
+			top = border;
+	}
 
 	if (!strict_kernel_rwx_enabled() || base >= border || top <= border)
 		return __mmu_mapin_ram(base, top);

arch/powerpc/mm/init_32.c

@@ -99,10 +99,9 @@ static void __init MMU_setup(void)
 	if (IS_ENABLED(CONFIG_PPC_8xx))
 		return;
 
-	if (debug_pagealloc_enabled()) {
-		__map_without_bats = 1;
+	if (debug_pagealloc_enabled())
 		__map_without_ltlbs = 1;
-	}
+
 	if (strict_kernel_rwx_enabled())
 		__map_without_ltlbs = 1;
 }