x86/fpu: Factor out FPU hw activation/deactivation

We have repeat patterns of:

	if (!use_eager_fpu())
		clts();

... to activate FPU registers, and:

	if (!use_eager_fpu())
		stts();

... to deactivate them.

Encapsulate these in:

	__fpregs_activate_hw();
	__fpregs_activate_hw();

and use them accordingly.

Doing this synchronizes the idiom with the fpu->fpregs_active
software-flag's handling functions, creating clear patterns of:

	__fpregs_activate_hw();
	__fpregs_activate(fpu);

etc., which improves readability.

Reviewed-by: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/fpu/internal.h

@@ -324,14 +324,31 @@ static inline int restore_fpu_checking(struct fpu *fpu)
 	return fpu_restore_checking(fpu);
 }
 
-/* Must be paired with an 'stts' after! */
+/*
+ * Wrap lazy FPU TS handling in a 'hw fpregs activation/deactivation'
+ * idiom, which is then paired with the sw-flag (fpregs_active) later on:
+ */
+
+static inline void __fpregs_activate_hw(void)
+{
+	if (!use_eager_fpu())
+		clts();
+}
+
+static inline void __fpregs_deactivate_hw(void)
+{
+	if (!use_eager_fpu())
+		stts();
+}
+
+/* Must be paired with an 'stts' (fpregs_deactivate_hw()) after! */
 static inline void __fpregs_deactivate(struct fpu *fpu)
 {
 	fpu->fpregs_active = 0;
 	this_cpu_write(fpu_fpregs_owner_ctx, NULL);
 }
 
-/* Must be paired with a 'clts' before! */
+/* Must be paired with a 'clts' (fpregs_activate_hw()) before! */
 static inline void __fpregs_activate(struct fpu *fpu)
 {
 	fpu->fpregs_active = 1;
@@ -362,16 +379,14 @@ static inline int user_has_fpu(void)
  */
 static inline void fpregs_activate(struct fpu *fpu)
 {
-	if (!use_eager_fpu())
+	__fpregs_activate_hw();
-		clts();
 	__fpregs_activate(fpu);
 }
 
 static inline void fpregs_deactivate(struct fpu *fpu)
 {
 	__fpregs_deactivate(fpu);
-	if (!use_eager_fpu())
+	__fpregs_deactivate_hw();
-		stts();
 }
 
 static inline void drop_fpu(struct fpu *fpu)
@@ -455,8 +470,9 @@ switch_fpu_prepare(struct fpu *old_fpu, struct fpu *new_fpu, int cpu)
 			new_fpu->counter++;
 			__fpregs_activate(new_fpu);
 			prefetch(&new_fpu->state);
-		} else if (!use_eager_fpu())
+		} else {
-			stts();
+			__fpregs_deactivate_hw();
+		}
 	} else {
 		old_fpu->counter = 0;
 		old_fpu->last_cpu = -1;

arch/x86/kernel/fpu/core.c

@@ -105,8 +105,7 @@ void __kernel_fpu_begin(void)
 		copy_fpregs_to_fpstate(fpu);
 	} else {
 		this_cpu_write(fpu_fpregs_owner_ctx, NULL);
-		if (!use_eager_fpu())
+		__fpregs_activate_hw();
-			clts();
 	}
 }
 EXPORT_SYMBOL(__kernel_fpu_begin);
@@ -118,8 +117,8 @@ void __kernel_fpu_end(void)
 	if (fpu->fpregs_active) {
 		if (WARN_ON(restore_fpu_checking(fpu)))
 			fpu_reset_state(fpu);
-	} else if (!use_eager_fpu()) {
+	} else {
-		stts();
+		__fpregs_deactivate_hw();
 	}
 
 	kernel_fpu_enable();