powerpc/mm: Move around testing of _PAGE_PRESENT in hash code

Instead of adding _PAGE_PRESENT to the access permission mask
in each low level routine independently, we add it once from
hash_page().

We also move the preliminary access check (the racy one before
the PTE is locked) up so it applies to the huge page case. This
duplicates code in __hash_page_huge() which we'll remove in a
subsequent patch to fix a race in there.

Signed-off-by: Benjamin Herrenschmidt <[e-mail]>

arch/powerpc/mm/hash_low_64.S

···
 	std	r8,STK_PARM(r8)(r1)
 	std	r9,STK_PARM(r9)(r1)
 	
-	/* Add _PAGE_PRESENT to access */
-	ori	r4,r4,_PAGE_PRESENT
-
 	/* Save non-volatile registers.
 	 * r31 will hold "old PTE"
 	 * r30 is "new PTE"
···
 	std	r6,STK_PARM(r6)(r1)
 	std	r8,STK_PARM(r8)(r1)
 	std	r9,STK_PARM(r9)(r1)
-
-	/* Add _PAGE_PRESENT to access */
-	ori	r4,r4,_PAGE_PRESENT
 
 	/* Save non-volatile registers.
 	 * r31 will hold "old PTE"
···
 	std	r6,STK_PARM(r6)(r1)
 	std	r8,STK_PARM(r8)(r1)
 	std	r9,STK_PARM(r9)(r1)
-
-	/* Add _PAGE_PRESENT to access */
-	ori	r4,r4,_PAGE_PRESENT
 
 	/* Save non-volatile registers.
 	 * r31 will hold "old PTE"

arch/powerpc/mm/hash_utils_64.c

···
 		return 1;
 	}
 
+	/* Add _PAGE_PRESENT to the required access perm */
+	access |= _PAGE_PRESENT;
+
+	/* Pre-check access permissions (will be re-checked atomically
+	 * in __hash_page_XX but this pre-check is a fast path
+	 */
+	if (access & ~pte_val(*ptep)) {
+		DBG_LOW(" no access !\n");
+		return 1;
+	}
+
 #ifdef CONFIG_HUGETLB_PAGE
 	if (hugeshift)
 		return __hash_page_huge(ea, access, vsid, ptep, trap, local,
···
 	DBG_LOW(" i-pte: %016lx %016lx\n", pte_val(*ptep),
 		pte_val(*(ptep + PTRS_PER_PTE)));
 #endif
-	/* Pre-check access permissions (will be re-checked atomically
-	 * in __hash_page_XX but this pre-check is a fast path
-	 */
-	if (access & ~pte_val(*ptep)) {
-		DBG_LOW(" no access !\n");
-		return 1;
-	}
-
 	/* Do actual hashing */
 #ifdef CONFIG_PPC_64K_PAGES
 	/* If _PAGE_4K_PFN is set, make sure this is a 4k segment */