x86/fpu: Factor out fpu__copy()

Introduce fpu__copy() and use it in arch_dup_task_struct(),
thus moving another chunk of FPU logic to fpu/core.c.

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

@@ -567,6 +567,7 @@ static inline unsigned short get_fpu_mxcsr(struct task_struct *tsk)
 extern void fpstate_cache_init(void);
 
 extern int fpstate_alloc(struct fpu *fpu);
+extern int fpu__copy(struct task_struct *dst, struct task_struct *src);
 
 static inline void fpstate_free(struct fpu *fpu)
 {

arch/x86/kernel/fpu/core.c

@@ -178,6 +178,24 @@ int fpstate_alloc(struct fpu *fpu)
 }
 EXPORT_SYMBOL_GPL(fpstate_alloc);
 
+int fpu__copy(struct task_struct *dst, struct task_struct *src)
+{
+	dst->thread.fpu.counter = 0;
+	dst->thread.fpu.has_fpu = 0;
+	dst->thread.fpu.state = NULL;
+
+	task_disable_lazy_fpu_restore(dst);
+
+	if (tsk_used_math(src)) {
+		int err = fpstate_alloc(&dst->thread.fpu);
+
+		if (err)
+			return err;
+		fpu_copy(dst, src);
+	}
+	return 0;
+}
+
 /*
  * Allocate the backing store for the current task's FPU registers
  * and initialize the registers themselves as well.

arch/x86/kernel/process.c

@@ -83,17 +83,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
 {
 	*dst = *src;
 
-	dst->thread.fpu.counter = 0;
-	dst->thread.fpu.has_fpu = 0;
-	dst->thread.fpu.state = NULL;
-	task_disable_lazy_fpu_restore(dst);
-	if (tsk_used_math(src)) {
-		int err = fpstate_alloc(&dst->thread.fpu);
-		if (err)
-			return err;
-		fpu_copy(dst, src);
-	}
-	return 0;
+	return fpu__copy(dst, src);
 }
 
 void arch_release_task_struct(struct task_struct *tsk)