[PATCH 2/4] x86/fpu: introduce restore_init_xstate()

[Oleg Nesterov]

Extract the "use_eager_fpu()" code from drop_init_fpu() into the new
simple helper, restore_init_xstate(). The next patch adds another user.

- It is not clear why we do not check use_fxsr() like fpu_restore_checking()
  does. eager_fpu_init_bp() calls setup_init_fpu_buf() too, and we have the
  "eagerfpu=on" kernel option.

- Ignoring the fact that init_xstate_buf is "struct xsave_struct *", not
  "union thread_xstate *", it is not clear why we can not simply use
  fpu_restore_checking() and avoid the code duplication.

- It is not clear why we can't call setup_init_fpu_buf() unconditionally
  to always create init_xstate_buf(). Then do_device_not_available() path
  (at least) could use restore_init_xstate() too. It doesn't need to init
  fpu->state, its content doesn't matter until unlazy_fpu/__switch_to/etc
  which overwrites this memory anyway.

Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
---
 arch/x86/include/asm/fpu-internal.h |   16 ++++++++++------
 1 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/x86/include/asm/fpu-internal.h b/arch/x86/include/asm/fpu-internal.h
index c615ae9..d1f8472 100644
--- a/arch/x86/include/asm/fpu-internal.h
+++ b/arch/x86/include/asm/fpu-internal.h
@@ -340,16 +340,20 @@ static inline void drop_fpu(struct task_struct *tsk)
 	preempt_enable();
 }
 
+static inline void restore_init_xstate(void)
+{
+	if (use_xsave())
+		xrstor_state(init_xstate_buf, -1);
+	else
+		fxrstor_checking(&init_xstate_buf->i387);
+}
+
 static inline void drop_init_fpu(struct task_struct *tsk)
 {
 	if (!use_eager_fpu())
 		drop_fpu(tsk);
-	else {
-		if (use_xsave())
-			xrstor_state(init_xstate_buf, -1);
-		else
-			fxrstor_checking(&init_xstate_buf->i387);
-	}
+	else
+		restore_init_xstate();
 }
 
 /*
-- 
1.5.5.1


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