powerpc/8xx: Allow large TLBs with DEBUG_PAGEALLOC

DEBUG_PAGEALLOC only manages RW data.

Text and RO data can still be mapped with hugepages and pinned TLB.

In order to map with hugepages, also enforce a 512kB data alignment
minimum. That's a trade-off between size of speed, taking into
account that DEBUG_PAGEALLOC is a debug option. Anyway the alignment
is still tunable.

We also allow tuning of alignment for book3s to limit the complexity
of the test in Kconfig that will anyway disappear in the following
patches once DEBUG_PAGEALLOC is handled together with BATs.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/c13256f2d356a316715da61fe089b3623ef217a5.1589866984.git.christophe.leroy@csgroup.eu

arch/powerpc/Kconfig

@@ -781,8 +781,9 @@ config THREAD_SHIFT
 config DATA_SHIFT_BOOL
 	bool "Set custom data alignment"
 	depends on ADVANCED_OPTIONS
-	depends on STRICT_KERNEL_RWX
-	depends on PPC_BOOK3S_32 || (PPC_8xx && !PIN_TLB_DATA && !PIN_TLB_TEXT)
+	depends on STRICT_KERNEL_RWX || DEBUG_PAGEALLOC
+	depends on PPC_BOOK3S_32 || (PPC_8xx && !PIN_TLB_DATA && \
+				     (!PIN_TLB_TEXT || !STRICT_KERNEL_RWX))
 	help
 	  This option allows you to set the kernel data alignment. When
 	  RAM is mapped by blocks, the alignment needs to fit the size and
@@ -793,10 +794,12 @@ config DATA_SHIFT_BOOL
 config DATA_SHIFT
 	int "Data shift" if DATA_SHIFT_BOOL
 	default 24 if STRICT_KERNEL_RWX && PPC64
-	range 17 28 if STRICT_KERNEL_RWX && PPC_BOOK3S_32
-	range 19 23 if STRICT_KERNEL_RWX && PPC_8xx
+	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 23 if STRICT_KERNEL_RWX && PPC_8xx
+	default 23 if DEBUG_PAGEALLOC && PPC_8xx && PIN_TLB_DATA
+	default 19 if DEBUG_PAGEALLOC && PPC_8xx
 	default PPC_PAGE_SHIFT
 	help
 	  On Book3S 32 (603+), DBATs are used to map kernel text and rodata RO.

arch/powerpc/mm/init_32.c

@@ -96,11 +96,14 @@ static void __init MMU_setup(void)
 	if (strstr(boot_command_line, "noltlbs")) {
 		__map_without_ltlbs = 1;
 	}
+	if (IS_ENABLED(CONFIG_PPC_8xx))
+		return;
+
 	if (debug_pagealloc_enabled()) {
 		__map_without_bats = 1;
 		__map_without_ltlbs = 1;
 	}
-	if (strict_kernel_rwx_enabled() && !IS_ENABLED(CONFIG_PPC_8xx))
+	if (strict_kernel_rwx_enabled())
 		__map_without_ltlbs = 1;
 }
 

arch/powerpc/mm/nohash/8xx.c

@@ -150,7 +150,8 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
 {
 	unsigned long etext8 = ALIGN(__pa(_etext), SZ_8M);
 	unsigned long sinittext = __pa(_sinittext);
-	unsigned long boundary = strict_kernel_rwx_enabled() ? sinittext : etext8;
+	bool strict_boundary = strict_kernel_rwx_enabled() || debug_pagealloc_enabled();
+	unsigned long boundary = strict_boundary ? sinittext : etext8;
 	unsigned long einittext8 = ALIGN(__pa(_einittext), SZ_8M);
 
 	WARN_ON(top < einittext8);
@@ -161,8 +162,12 @@ unsigned long __init mmu_mapin_ram(unsigned long base, unsigned long top)
 		return 0;
 
 	mmu_mapin_ram_chunk(0, boundary, PAGE_KERNEL_TEXT, true);
-	mmu_mapin_ram_chunk(boundary, einittext8, PAGE_KERNEL_TEXT, true);
-	mmu_mapin_ram_chunk(einittext8, top, PAGE_KERNEL, true);
+	if (debug_pagealloc_enabled()) {
+		top = boundary;
+	} else {
+		mmu_mapin_ram_chunk(boundary, einittext8, PAGE_KERNEL_TEXT, true);
+		mmu_mapin_ram_chunk(einittext8, top, PAGE_KERNEL, true);
+	}
 
 	if (top > SZ_32M)
 		memblock_set_current_limit(top);

arch/powerpc/platforms/8xx/Kconfig

@@ -167,7 +167,7 @@ menu "8xx advanced setup"
 
 config PIN_TLB
 	bool "Pinned Kernel TLBs"
-	depends on ADVANCED_OPTIONS && !DEBUG_PAGEALLOC
+	depends on ADVANCED_OPTIONS
 	help
 	  On the 8xx, we have 32 instruction TLBs and 32 data TLBs. In each
 	  table 4 TLBs can be pinned.