MIPS: 16 byte align MSA vector context

The MSA specification upon first read appears to suggest that it is safe
to perform vector loads & stores with arbitrary alignment. However it
leaves provision for "address-dependent exceptions"... Align the vector
context to a 16 byte boundary to ensure that the kernel cannot cause any
such exceptions.

Note that the fpu field of struct thread_struct was already at a 16 byte
boundary within the struct, the introduction of FPU_ALIGN simply makes
the requirement explicit. The only part of this impacting the generated
kernel binary is ARCH_MIN_TASKALIGN.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7308/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/processor.h

@@ -238,7 +238,13 @@ typedef struct {
 	unsigned long seg;
 } mm_segment_t;
 
-#define ARCH_MIN_TASKALIGN	8
+#ifdef CONFIG_CPU_HAS_MSA
+# define ARCH_MIN_TASKALIGN	16
+# define FPU_ALIGN		__aligned(16)
+#else
+# define ARCH_MIN_TASKALIGN	8
+# define FPU_ALIGN
+#endif
 
 struct mips_abi;
 
@@ -255,7 +261,7 @@ struct thread_struct {
 	unsigned long cp0_status;
 
 	/* Saved fpu/fpu emulator stuff. */
-	struct mips_fpu_struct fpu;
+	struct mips_fpu_struct fpu FPU_ALIGN;
 #ifdef CONFIG_MIPS_MT_FPAFF
 	/* Emulated instruction count */
 	unsigned long emulated_fp;