x86/fpu: Make the system/cpu init distinction clear in the xstate code as well

Rename existing xstate init functions along the system/cpu init principles:

	fpu__init_system_xstate(): called once per system bootup
	fpu__init_cpu_xstate():    called per CPU onlining

Also make the fpu__init_cpu_xstate() early code invariant:
if xfeatures_mask is not set yet then don't crash but return.
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

@@ -39,6 +39,9 @@ extern unsigned int mxcsr_feature_mask;
 extern void fpu__cpu_init(void);
 extern void eager_fpu_init(void);
 
+extern void fpu__init_system_xstate(void);
+extern void fpu__init_cpu_xstate(void);
+
 DECLARE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
 
 extern void convert_from_fxsr(struct user_i387_ia32_struct *env,

arch/x86/kernel/fpu/xsave.c

@@ -460,10 +460,14 @@ static void prepare_fx_sw_frame(void)
 }
 
 /*
- * Enable the extended processor state save/restore feature
+ * Enable the extended processor state save/restore feature.
+ * Called once per CPU onlining.
  */
-static inline void xstate_enable(void)
+void fpu__init_cpu_xstate(void)
 {
+	if (!xfeatures_mask)
+		return;
+
 	cr4_set_bits(X86_CR4_OSXSAVE);
 	xsetbv(XCR_XFEATURE_ENABLED_MASK, xfeatures_mask);
 }
@@ -640,11 +644,12 @@ static void __init init_xstate_size(void)
 
 /*
  * Enable and initialize the xsave feature.
+ * Called once per system bootup.
  *
  * ( Not marked __init because of false positive section warnings
  *   generated by xsave_init(). )
  */
-static void /* __init */ xstate_enable_boot_cpu(void)
+void fpu__init_system_xstate(void)
 {
 	unsigned int eax, ebx, ecx, edx;
 
@@ -666,7 +671,8 @@ static void /* __init */ xstate_enable_boot_cpu(void)
 	 */
 	xfeatures_mask = xfeatures_mask & XCNTXT_MASK;
 
-	xstate_enable();
+	/* Enable xstate instructions to be able to continue with initialization: */
+	fpu__init_cpu_xstate();
 
 	/*
 	 * Recompute the context size for enabled features
@@ -698,8 +704,8 @@ static void /* __init */ xstate_enable_boot_cpu(void)
 }
 
 /*
- * For the very first instance, this calls xstate_enable_boot_cpu();
- * for all subsequent instances, this calls xstate_enable().
+ * For the very first instance, this calls fpu__init_system_xstate();
+ * for all subsequent instances, this calls fpu__init_cpu_xstate().
  */
 void xsave_init(void)
 {
@@ -715,9 +721,9 @@ void xsave_init(void)
 
 	if (on_boot_cpu) {
 		on_boot_cpu = 0;
-		xstate_enable_boot_cpu();
+		fpu__init_system_xstate();
 	} else {
-		xstate_enable();
+		fpu__init_cpu_xstate();
 	}
 }