init: Invoke init_espfix_bsp() from mm_init()

init_espfix_bsp() needs to be invoked before the page table isolation
initialization. Move it into mm_init() which is the place where pti_init()
will be added.

While at it get rid of the #ifdeffery and provide proper stub functions.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/include/asm/espfix.h

@@ -2,7 +2,7 @@
 #ifndef _ASM_X86_ESPFIX_H
 #define _ASM_X86_ESPFIX_H
 
-#ifdef CONFIG_X86_64
+#ifdef CONFIG_X86_ESPFIX64
 
 #include <asm/percpu.h>
 
@@ -11,7 +11,8 @@ DECLARE_PER_CPU_READ_MOSTLY(unsigned long, espfix_waddr);
 
 extern void init_espfix_bsp(void);
 extern void init_espfix_ap(int cpu);
-
-#endif /* CONFIG_X86_64 */
+#else
+static inline void init_espfix_ap(int cpu) { }
+#endif
 
 #endif /* _ASM_X86_ESPFIX_H */

arch/x86/kernel/smpboot.c

@@ -990,12 +990,8 @@ static int do_boot_cpu(int apicid, int cpu, struct task_struct *idle,
 	initial_code = (unsigned long)start_secondary;
 	initial_stack  = idle->thread.sp;
 
-	/*
-	 * Enable the espfix hack for this CPU
-	*/
-#ifdef CONFIG_X86_ESPFIX64
+	/* Enable the espfix hack for this CPU */
 	init_espfix_ap(cpu);
-#endif
 
 	/* So we see what's up */
 	announce_cpu(cpu, apicid);

include/asm-generic/pgtable.h

@@ -1017,6 +1017,11 @@ static inline int pmd_clear_huge(pmd_t *pmd)
 struct file;
 int phys_mem_access_prot_allowed(struct file *file, unsigned long pfn,
 			unsigned long size, pgprot_t *vma_prot);
+
+#ifndef CONFIG_X86_ESPFIX64
+static inline void init_espfix_bsp(void) { }
+#endif
+
 #endif /* !__ASSEMBLY__ */
 
 #ifndef io_remap_pfn_range

init/main.c

@@ -504,6 +504,8 @@ static void __init mm_init(void)
 	pgtable_init();
 	vmalloc_init();
 	ioremap_huge_init();
+	/* Should be run before the first non-init thread is created */
+	init_espfix_bsp();
 }
 
 asmlinkage __visible void __init start_kernel(void)
@@ -673,10 +675,6 @@ asmlinkage __visible void __init start_kernel(void)
 #ifdef CONFIG_X86
 	if (efi_enabled(EFI_RUNTIME_SERVICES))
 		efi_enter_virtual_mode();
-#endif
-#ifdef CONFIG_X86_ESPFIX64
-	/* Should be run before the first non-init thread is created */
-	init_espfix_bsp();
 #endif
 	thread_stack_cache_init();
 	cred_init();