x86/idt: Move early IDT handler setup to IDT code

The early IDT handler setup is done in C entry code on 64-bit kernels and in
ASM entry code on 32-bit kernels.

Move the 64-bit variant to the IDT code so it can be shared with 32-bit
in the next step.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Steven Rostedt <rostedt@goodmis.org>
Link: http://lkml.kernel.org/r/20170828064958.679561404@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/desc.h

@@ -504,6 +504,15 @@ static inline void load_current_idt(void)
 		load_idt((const struct desc_ptr *)&idt_descr);
 }
 
+extern void idt_setup_early_handler(void);
+extern void idt_setup_early_traps(void);
+
+#ifdef CONFIG_X86_64
+extern void idt_setup_early_pf(void);
+#else
+static inline void idt_setup_early_pf(void) { }
+#endif
+
 extern void idt_invalidate(void *addr);
 
 #endif /* _ASM_X86_DESC_H */

arch/x86/kernel/head64.c

@@ -255,8 +255,6 @@ static void __init copy_bootdata(char *real_mode_data)
 
 asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 {
-	int i;
-
 	/*
 	 * Build-time sanity checks on the kernel image and module
 	 * area mappings. (these are purely build-time and produce no code)
@@ -282,9 +280,7 @@ asmlinkage __visible void __init x86_64_start_kernel(char * real_mode_data)
 
 	kasan_early_init();
 
-	for (i = 0; i < NUM_EXCEPTION_VECTORS; i++)
-		set_intr_gate(i, early_idt_handler_array[i]);
-	load_idt((const struct desc_ptr *)&idt_descr);
+	idt_setup_early_handler();
 
 	copy_bootdata(__va(real_mode_data));
 

arch/x86/kernel/idt.c

@@ -25,6 +25,18 @@ const struct desc_ptr debug_idt_descr = {
 };
 #endif
 
+/**
+ * idt_setup_early_handler - Initializes the idt table with early handlers
+ */
+void __init idt_setup_early_handler(void)
+{
+	int i;
+
+	for (i = 0; i < NUM_EXCEPTION_VECTORS; i++)
+		set_intr_gate(i, early_idt_handler_array[i]);
+	load_idt(&idt_descr);
+}
+
 /**
  * idt_invalidate - Invalidate interrupt descriptor table
  * @addr:	The virtual address of the 'invalid' IDT