mm/gup: Move permission checks into helpers

This is a preparation patch for the transition of x86 to the generic GUP_fast()
implementation.

On x86, we would need to do additional permission checks to determine if
access is allowed.

Let's abstract it out into separate helpers.

Signed-off-by: Kirill A. Shutemov <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Aneesh Kumar K . V <[e-mail]>
Cc: Borislav Petkov <[e-mail]>
Cc: Catalin Marinas <[e-mail]>
Cc: Dann Frazier <[e-mail]>
Cc: Dave Hansen <[e-mail]>
Cc: H. Peter Anvin <[e-mail]>
Cc: Linus Torvalds <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Rik van Riel <[e-mail]>
Cc: Steve Capper <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Ingo Molnar <[e-mail]>

include/asm-generic/pgtable.h

···
 }
 #endif
 
+#ifndef pte_access_permitted
+#define pte_access_permitted(pte, write) \
+	(pte_present(pte) && (!(write) || pte_write(pte)))
+#endif
+
+#ifndef pmd_access_permitted
+#define pmd_access_permitted(pmd, write) \
+	(pmd_present(pmd) && (!(write) || pmd_write(pmd)))
+#endif
+
+#ifndef pud_access_permitted
+#define pud_access_permitted(pud, write) \
+	(pud_present(pud) && (!(write) || pud_write(pud)))
+#endif
+
+#ifndef p4d_access_permitted
+#define p4d_access_permitted(p4d, write) \
+	(p4d_present(p4d) && (!(write) || p4d_write(p4d)))
+#endif
+
+#ifndef pgd_access_permitted
+#define pgd_access_permitted(pgd, write) \
+	(pgd_present(pgd) && (!(write) || pgd_write(pgd)))
+#endif
+
 #ifndef __HAVE_ARCH_PMD_SAME
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
 static inline int pmd_same(pmd_t pmd_a, pmd_t pmd_b)

mm/gup.c

···
 		 * Similar to the PMD case below, NUMA hinting must take slow
 		 * path using the pte_protnone check.
 		 */
-		if (!pte_present(pte) || pte_special(pte) ||
-			pte_protnone(pte) || (write && !pte_write(pte)))
+		if (pte_protnone(pte))
+			goto pte_unmap;
+
+		if (!pte_access_permitted(pte, write))
+			goto pte_unmap;
+
+		if (pte_special(pte))
 			goto pte_unmap;
 
 		VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
···
 	struct page *head, *page;
 	int refs;
 
-	if (write && !pmd_write(orig))
+	if (!pmd_access_permitted(orig, write))
 		return 0;
 
 	refs = 0;
···
 	struct page *head, *page;
 	int refs;
 
-	if (write && !pud_write(orig))
+	if (!pud_access_permitted(orig, write))
 		return 0;
 
 	refs = 0;
···
 	int refs;
 	struct page *head, *page;
 
-	if (write && !pgd_write(orig))
+	if (!pgd_access_permitted(orig, write))
 		return 0;
 
 	refs = 0;