x86: strengthen 64-bit p?d_bad()

The x86_64 pgd_bad(), pud_bad(), pmd_bad() inlines have differed from
their x86_32 counterparts in a couple of ways: they've been unnecessarily
weak (e.g. letting 0 or 1 count as good), and were typed as unsigned long.
Strengthen them and return int.

The PAE pmd_bad was too weak before, allowing any junk in the upper half;
but got strengthened by the patch correcting its ~PAGE_MASK to ~PTE_MASK.
The PAE pud_bad already said ~PTE_MASK; and since it folds into pgd_bad,
and we don't set the protection bits at that level, it'll do as is.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/asm-x86/pgtable_64.h

@@ -151,19 +151,19 @@ static inline void native_pgd_clear(pgd_t *pgd)
 
 #ifndef __ASSEMBLY__
 
-static inline unsigned long pgd_bad(pgd_t pgd)
+static inline int pgd_bad(pgd_t pgd)
 {
-	return pgd_val(pgd) & ~(PTE_MASK | _KERNPG_TABLE | _PAGE_USER);
+	return (pgd_val(pgd) & ~(PTE_MASK | _PAGE_USER)) != _KERNPG_TABLE;
 }
 
-static inline unsigned long pud_bad(pud_t pud)
+static inline int pud_bad(pud_t pud)
 {
-	return pud_val(pud) & ~(PTE_MASK | _KERNPG_TABLE | _PAGE_USER);
+	return (pud_val(pud) & ~(PTE_MASK | _PAGE_USER)) != _KERNPG_TABLE;
 }
 
-static inline unsigned long pmd_bad(pmd_t pmd)
+static inline int pmd_bad(pmd_t pmd)
 {
-	return pmd_val(pmd) & ~(PTE_MASK | _KERNPG_TABLE | _PAGE_USER);
+	return (pmd_val(pmd) & ~(PTE_MASK | _PAGE_USER)) != _KERNPG_TABLE;
 }
 
 #define pte_none(x)	(!pte_val((x)))