powerpc/64s: Reduce exception alignment

Exception handlers are aligned to 128 bytes (L1 cache) on 64s, which is
overkill. It can reduce the icache footprint of any individual exception
path. However taken as a whole, the expansion in icache footprint seems
likely to be counter-productive and cause more total misses.

Create IFETCH_ALIGN_SHIFT/BYTES, which should give optimal ifetch
alignment with much more reasonable alignment. This saves 1792 bytes
from head_64.o text with an allmodconfig build.

Other subarchitectures should define appropriate IFETCH_ALIGN_SHIFT
values if this becomes more widely used.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/include/asm/cache.h

@@ -20,12 +20,15 @@
 #endif
 #else /* CONFIG_PPC64 */
 #define L1_CACHE_SHIFT		7
+#define IFETCH_ALIGN_SHIFT	4 /* POWER8,9 */
 #endif
 
 #define	L1_CACHE_BYTES		(1 << L1_CACHE_SHIFT)
 
 #define	SMP_CACHE_BYTES		L1_CACHE_BYTES
 
+#define IFETCH_ALIGN_BYTES	(1 << IFETCH_ALIGN_SHIFT)
+
 #if defined(__powerpc64__) && !defined(__ASSEMBLY__)
 struct ppc64_caches {
 	u32	dsize;			/* L1 d-cache size */

arch/powerpc/include/asm/head-64.h

@@ -95,12 +95,12 @@ end_##sname:
 
 #define __FIXED_SECTION_ENTRY_BEGIN(sname, name, __align)	\
 	USE_FIXED_SECTION(sname);				\
-	.align __align;						\
+	.balign __align;					\
 	.global name;						\
 name:
 
 #define FIXED_SECTION_ENTRY_BEGIN(sname, name)			\
-	__FIXED_SECTION_ENTRY_BEGIN(sname, name, 0)
+	__FIXED_SECTION_ENTRY_BEGIN(sname, name, IFETCH_ALIGN_BYTES)
 
 #define FIXED_SECTION_ENTRY_BEGIN_LOCATION(sname, name, start)		\
 	USE_FIXED_SECTION(sname);				\
@@ -205,7 +205,7 @@ name:
 
 #define EXC_COMMON_BEGIN(name)						\
 	USE_TEXT_SECTION();						\
-	.align	7;							\
+	.balign IFETCH_ALIGN_BYTES;					\
 	.global name;							\
 	DEFINE_FIXED_SYMBOL(name);					\
 name:

arch/powerpc/kernel/exceptions-64s.S

@@ -1403,7 +1403,7 @@ USE_TEXT_SECTION()
 /*
  * Hash table stuff
  */
-	.align	7
+	.balign	IFETCH_ALIGN_BYTES
 do_hash_page:
 #ifdef CONFIG_PPC_STD_MMU_64
 	andis.	r0,r4,0xa410		/* weird error? */