powerpc/nohash: Refactor checking of no-change in pte_update()

On nohash/64, a few callers of pte_update() check if there is
really a change in order to avoid an unnecessary write.

Refactor that inside pte_update().

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/076563e611c2b51036686a8d378bfd5ef1726341.1695659959.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/nohash/64/pgtable.h

@@ -181,8 +181,6 @@ static inline int __ptep_test_and_clear_young(struct mm_struct *mm,
 {
 	unsigned long old;
 
-	if (!pte_young(*ptep))
-		return 0;
 	old = pte_update(mm, addr, ptep, _PAGE_ACCESSED, 0, 0);
 	return (old & _PAGE_ACCESSED) != 0;
 }
@@ -198,20 +196,13 @@ static inline int __ptep_test_and_clear_young(struct mm_struct *mm,
 static inline void ptep_set_wrprotect(struct mm_struct *mm, unsigned long addr,
 				      pte_t *ptep)
 {
-
-	if ((pte_val(*ptep) & _PAGE_RW) == 0)
-		return;
-
 	pte_update(mm, addr, ptep, _PAGE_RW, 0, 0);
 }
 
 #define __HAVE_ARCH_HUGE_PTEP_SET_WRPROTECT
 static inline void huge_ptep_set_wrprotect(struct mm_struct *mm,
 					   unsigned long addr, pte_t *ptep)
 {
-	if ((pte_val(*ptep) & _PAGE_RW) == 0)
-		return;
-
 	pte_update(mm, addr, ptep, _PAGE_RW, 0, 1);
 }
 

arch/powerpc/include/asm/nohash/pgtable.h

@@ -47,6 +47,9 @@ static inline pte_basic_t pte_update(struct mm_struct *mm, unsigned long addr, p
 	pte_basic_t old = pte_val(*p);
 	pte_basic_t new = (old & ~(pte_basic_t)clr) | set;
 
+	if (new == old)
+		return old;
+
 	*p = __pte(new);
 
 	if (IS_ENABLED(CONFIG_44x) && (old & _PAGE_USER) && (old & _PAGE_EXEC))