x86/mm: Stop pretending pgtable_l5_enabled is a variable

pgtable_l5_enabled is defined using cpu_feature_enabled() but we refer
to it as a variable. This is misleading.

Make pgtable_l5_enabled() a function.

We cannot literally define it as a function due to circular dependencies
between header files. Function-alike macros is close enough.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20180518103528.59260-4-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 73bd8c9..77ec014 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -439,7 +439,7 @@ static noinline int vmalloc_fault(unsigned long address)
 	if (pgd_none(*pgd_k))
 		return -1;
 
-	if (pgtable_l5_enabled) {
+	if (pgtable_l5_enabled()) {
 		if (pgd_none(*pgd)) {
 			set_pgd(pgd, *pgd_k);
 			arch_flush_lazy_mmu_mode();
@@ -454,7 +454,7 @@ static noinline int vmalloc_fault(unsigned long address)
 	if (p4d_none(*p4d_k))
 		return -1;
 
-	if (p4d_none(*p4d) && !pgtable_l5_enabled) {
+	if (p4d_none(*p4d) && !pgtable_l5_enabled()) {
 		set_p4d(p4d, *p4d_k);
 		arch_flush_lazy_mmu_mode();
 	} else {