x86: make mm/gup.c more virtualization friendly

Since pte_flags() is much cheaper than pte_val() in some virtualized
environments (namely, Xen), use the former whereever possible.
Signed-off-by: Jan Beulich <jbeulich@novell.com>
Cc: "Nick Piggin" <npiggin@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/mm/gup.c

@@ -82,7 +82,7 @@ static noinline int gup_pte_range(pmd_t pmd, unsigned long addr,
 		pte_t pte = gup_get_pte(ptep);
 		struct page *page;
 
-		if ((pte_val(pte) & (mask | _PAGE_SPECIAL)) != mask) {
+		if ((pte_flags(pte) & (mask | _PAGE_SPECIAL)) != mask) {
 			pte_unmap(ptep);
 			return 0;
 		}
@@ -116,10 +116,10 @@ static noinline int gup_huge_pmd(pmd_t pmd, unsigned long addr,
 	mask = _PAGE_PRESENT|_PAGE_USER;
 	if (write)
 		mask |= _PAGE_RW;
-	if ((pte_val(pte) & mask) != mask)
+	if ((pte_flags(pte) & mask) != mask)
 		return 0;
 	/* hugepages are never "special" */
-	VM_BUG_ON(pte_val(pte) & _PAGE_SPECIAL);
+	VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
 	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 
 	refs = 0;
@@ -173,10 +173,10 @@ static noinline int gup_huge_pud(pud_t pud, unsigned long addr,
 	mask = _PAGE_PRESENT|_PAGE_USER;
 	if (write)
 		mask |= _PAGE_RW;
-	if ((pte_val(pte) & mask) != mask)
+	if ((pte_flags(pte) & mask) != mask)
 		return 0;
 	/* hugepages are never "special" */
-	VM_BUG_ON(pte_val(pte) & _PAGE_SPECIAL);
+	VM_BUG_ON(pte_flags(pte) & _PAGE_SPECIAL);
 	VM_BUG_ON(!pfn_valid(pte_pfn(pte)));
 
 	refs = 0;

include/asm-x86/pgtable.h

@@ -206,7 +206,7 @@ static inline int pte_exec(pte_t pte)
 
 static inline int pte_special(pte_t pte)
 {
-	return pte_val(pte) & _PAGE_SPECIAL;
+	return pte_flags(pte) & _PAGE_SPECIAL;
 }
 
 static inline unsigned long pte_pfn(pte_t pte)