MIPS: save/disable MSA in lose_fpu

The kernel depends upon MSA never being enabled when the FPU is not, a
condition which is currently violated in a few places (whilst saving
sigcontext, following mips_cpu_save). Catch all the problem cases by
disabling MSA in lose_fpu, after saving context if necessary.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7302/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/fpu.h

@@ -21,6 +21,7 @@
 #include <asm/hazards.h>
 #include <asm/processor.h>
 #include <asm/current.h>
+#include <asm/msa.h>
 
 #ifdef CONFIG_MIPS_MT_FPAFF
 #include <asm/mips_mt.h>
@@ -141,13 +142,21 @@ static inline int own_fpu(int restore)
 static inline void lose_fpu(int save)
 {
 	preempt_disable();
-	if (is_fpu_owner()) {
+	if (is_msa_enabled()) {
+		if (save) {
+			save_msa(current);
+			asm volatile("cfc1 %0, $31"
+				: "=r"(current->thread.fpu.fcr31));
+		}
+		disable_msa();
+		clear_thread_flag(TIF_USEDMSA);
+	} else if (is_fpu_owner()) {
 		if (save)
 			_save_fp(current);
-		KSTK_STATUS(current) &= ~ST0_CU1;
-		clear_thread_flag(TIF_USEDFPU);
 		__disable_fpu();
 	}
+	KSTK_STATUS(current) &= ~ST0_CU1;
+	clear_thread_flag(TIF_USEDFPU);
 	preempt_enable();
 }