x86/fpu: Split old & new FPU code paths

Now that CR0.TS is no longer being manipulated, we can simplify
switch_fpu_prepare() by no longer nesting the handling of new_fpu
inside the two branches for the old_fpu.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Quentin Casasnovas <quentin.casasnovas@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: pbonzini@redhat.com
Link: http://lkml.kernel.org/r/1475627678-20788-10-git-send-email-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

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

@@ -581,23 +581,17 @@ switch_fpu_prepare(struct fpu *old_fpu, struct fpu *new_fpu, int cpu)
 		/* But leave fpu_fpregs_owner_ctx! */
 		old_fpu->fpregs_active = 0;
 		trace_x86_fpu_regs_deactivated(old_fpu);
+	} else
+		old_fpu->last_cpu = -1;
 
-		/* Don't change CR0.TS if we just switch! */
-		if (fpu.preload) {
-			fpregs_activate(new_fpu);
-			trace_x86_fpu_regs_activated(new_fpu);
+	if (fpu.preload) {
+		if (fpregs_state_valid(new_fpu, cpu))
+			fpu.preload = 0;
+		else
 			prefetch(&new_fpu->state);
-		}
-	} else {
-		old_fpu->last_cpu = -1;
-		if (fpu.preload) {
-			if (fpregs_state_valid(new_fpu, cpu))
-				fpu.preload = 0;
-			else
-				prefetch(&new_fpu->state);
-			fpregs_activate(new_fpu);
-		}
+		fpregs_activate(new_fpu);
 	}
+
 	return fpu;
 }