x86/fpu: Split fpu__cpu_init() into early-boot and cpu-boot parts

There are two kinds of FPU initialization sequences necessary to bring FPU
functionality up: once per system bootup activities, such as detection,
feature initialization, etc. of attributes that are shared by all CPUs
in the system - and per cpu initialization sequences run when a CPU is
brought online (either during bootup or during CPU hotplug onlining),
such as CR0/CR4 register setting, etc.

The FPU code is mixing these roles together, with no clear distinction.

Start sorting this out by splitting the main FPU detection routine
(fpu__cpu_init()) into two parts: fpu__init_system() for
one per system init activities, and fpu__init_cpu() for the
per CPU onlining init activities.

Note that xstate_init() is called from both variants for the time being,
because it has a dual nature as well. We'll fix that in upcoming patches.

Just do the split and call it as we used to before, don't introduce any
change in initialization behavior yet, beyond duplicate (and harmless)
fpu__init_cpu() and xstate_init() calls - which we'll fix in later
patches.
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

@@ -118,13 +118,9 @@ static void fpstate_xstate_init_size(void)
 }
 
 /*
- * Called on the boot CPU at bootup to set up the initial FPU state that
- * is later cloned into all processes.
- *
- * Also called on secondary CPUs to set up the FPU state of their
- * idle threads.
+ * Enable all supported FPU features. Called when a CPU is brought online.
  */
-void fpu__cpu_init(void)
+void fpu__init_cpu(void)
 {
 	unsigned long cr0;
 	unsigned long cr4_mask = 0;
@@ -150,12 +146,29 @@ void fpu__cpu_init(void)
 		cr0 |= X86_CR0_EM;
 	write_cr0(cr0);
 
+	xsave_init();
+}
+
+/*
+ * Called on the boot CPU once per system bootup, to set up the initial FPU state that
+ * is later cloned into all processes.
+ */
+void fpu__init_system(void)
+{
+	/* The FPU has to be operational for some of the later FPU init activities: */
+	fpu__init_cpu();
 
 	mxcsr_feature_mask_init();
 	xsave_init();
 	eager_fpu_init();
 }
 
+void fpu__cpu_init(void)
+{
+	fpu__init_cpu();
+	fpu__init_system();
+}
+
 static int __init no_387(char *s)
 {
 	setup_clear_cpu_cap(X86_FEATURE_FPU);