generic/pgtable: Introduce {p4d,pgd}_same()

In preparation for introducing '_safe' versions of page table entry 'set'
helpers, introduce generic versions of p4d_same() and pgd_same().
Signed-off-by: NDan Williams <dan.j.williams@intel.com>
Acked-by: NKirill A. Shutemov <kirill.shutemov@linux.intel.com>
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: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@surriel.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/154395943153.32119.1733586547359626311.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: NIngo Molnar <mingo@kernel.org>

include/asm-generic/pgtable.h

@@ -386,6 +386,20 @@ static inline int pud_same(pud_t pud_a, pud_t pud_b)
 }
 #endif
 
+#ifndef __HAVE_ARCH_P4D_SAME
+static inline int p4d_same(p4d_t p4d_a, p4d_t p4d_b)
+{
+	return p4d_val(p4d_a) == p4d_val(p4d_b);
+}
+#endif
+
+#ifndef __HAVE_ARCH_PGD_SAME
+static inline int pgd_same(pgd_t pgd_a, pgd_t pgd_b)
+{
+	return pgd_val(pgd_a) == pgd_val(pgd_b);
+}
+#endif
+
 #ifndef __HAVE_ARCH_DO_SWAP_PAGE
 /*
  * Some architectures support metadata associated with a page. When a