x86/fpu: Make setup_init_fpu_buf() run-once explicitly

Remove the dependency on the init_xstate_buf == NULL check to
implement once-per-bootup logic in eager_fpu_init(), by making
setup_init_fpu_buf() run once per bootup explicitly.

This is in preparation to make init_xstate_buf statically
allocated.

The various boot-once quirks in the FPU init code will be removed
in a later cleanup stage.
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/kernel/fpu/xsave.c

@@ -565,8 +565,14 @@ void setup_xstate_comp(void)
 /*
  * setup the xstate image representing the init state
  */
-static void __init setup_init_fpu_buf(void)
+static void setup_init_fpu_buf(void)
 {
+	static int on_boot_cpu = 1;
+
+	if (!on_boot_cpu)
+		return;
+	on_boot_cpu = 0;
+
 	/*
 	 * Setup init_xstate_buf to represent the init state of
 	 * all the features managed by the xsave
@@ -738,8 +744,7 @@ void __init_refok eager_fpu_init(void)
 		return;
 	}
 
-	if (!init_xstate_buf)
-		setup_init_fpu_buf();
+	setup_init_fpu_buf();
 }
 
 /*