x86: debug pmd_bad()

Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/pgtable_32.c

@@ -381,3 +381,10 @@ void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
 }
 
 #endif
+
+int pmd_bad(pmd_t pmd)
+{
+	WARN_ON_ONCE(pmd_bad_v1(pmd) != pmd_bad_v2(pmd));
+
+	return pmd_bad_v1(pmd);
+}

include/asm-x86/pgtable_32.h

@@ -90,7 +90,11 @@ extern unsigned long pg0[];
 /* To avoid harmful races, pmd_none(x) should check only the lower when PAE */
 #define pmd_none(x)	(!(unsigned long)pmd_val(x))
 #define pmd_present(x)	(pmd_val(x) & _PAGE_PRESENT)
-#define	pmd_bad(x)	((pmd_val(x) \
+
+extern int pmd_bad(pmd_t pmd);
+
+#define pmd_bad_v1(x)	((pmd_val(x) & (~PAGE_MASK & ~_PAGE_USER)) != _KERNPG_TABLE)
+#define	pmd_bad_v2(x)	((pmd_val(x) \
 			  & ~(PAGE_MASK | _PAGE_USER | _PAGE_PSE | _PAGE_NX)) \
 			 != _KERNPG_TABLE)