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 <kirill.shutemov@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Aneesh Kumar K . V <aneesh.kumar@linux.vnet.ibm.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Dann Frazier <dann.frazier@canonical.com>
Cc: Dave Hansen <dave.hansen@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@redhat.com>
Cc: Steve Capper <steve.capper@linaro.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-arch@vger.kernel.org
Cc: linux-mm@kvack.org
Link: http://lkml.kernel.org/r/20170316152655.37789-3-kirill.shutemov@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

include/asm-generic/pgtable.h

@@ -341,6 +341,31 @@ static inline int pte_unused(pte_t pte)
 }
 #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

@@ -1212,8 +1212,13 @@ static int gup_pte_range(pmd_t pmd, unsigned long addr, unsigned long end,
 		 * 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)));
@@ -1264,7 +1269,7 @@ static int gup_huge_pmd(pmd_t orig, pmd_t *pmdp, unsigned long addr,
 	struct page *head, *page;
 	int refs;
 
-	if (write && !pmd_write(orig))
+	if (!pmd_access_permitted(orig, write))
 		return 0;
 
 	refs = 0;
@@ -1299,7 +1304,7 @@ static int gup_huge_pud(pud_t orig, pud_t *pudp, unsigned long addr,
 	struct page *head, *page;
 	int refs;
 
-	if (write && !pud_write(orig))
+	if (!pud_access_permitted(orig, write))
 		return 0;
 
 	refs = 0;
@@ -1335,7 +1340,7 @@ static int gup_huge_pgd(pgd_t orig, pgd_t *pgdp, unsigned long addr,
 	int refs;
 	struct page *head, *page;
 
-	if (write && !pgd_write(orig))
+	if (!pgd_access_permitted(orig, write))
 		return 0;
 
 	refs = 0;