x86/fpu: Set up the legacy FPU init image from fpu__init_system()

The legacy FPU init image is used on older CPUs who don't run xstate init.
But the init code is called within setup_init_fpu_buf(), an xstate method.

Move this legacy init out of the xstate code and put it into fpu/init.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/kernel/fpu/init.c

@@ -158,6 +158,12 @@ void fpu__init_system(void)
 	/* The FPU has to be operational for some of the later FPU init activities: */
 	fpu__init_cpu();
 
+	/*
+	 * Set up the legacy init FPU context. (xstate init might overwrite this
+	 * with a more modern format, if the CPU supports it.)
+	 */
+	fx_finit(&init_xstate_ctx.i387);
+
 	mxcsr_feature_mask_init();
 	fpu__init_system_xstate();
 	eager_fpu_init();

arch/x86/kernel/fpu/xsave.c

@@ -576,12 +576,6 @@ static void setup_init_fpu_buf(void)
 		return;
 	on_boot_cpu = 0;
 
-	/*
-	 * Setup init_xstate_ctx to represent the init state of
-	 * all the features managed by the xsave
-	 */
-	fx_finit(&init_xstate_ctx.i387);
-
 	if (!cpu_has_xsave)
 		return;