s390/jump_label: replace stop_machine with smp_call_function

The use of stop_machine to replace the mask bits of the jump label branch
is a very heavy-weight operation. This is in fact not necessary, the
mask of the branch can simply be updated, followed by a signal processor
to all the other CPUs to force them to pick up the modified instruction.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
[heiko.carstens@de.ibm.com]: Change jump_label_make_nop() so we get
                             brcl 0,offset instead of brcl 0,0. This
                             makes sure that only the mask part of the
                             instruction gets changed when updated.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>

arch/s390/kernel/jump_label.c

@@ -22,9 +22,9 @@ struct insn_args {
 
 static void jump_label_make_nop(struct jump_entry *entry, struct insn *insn)
 {
-	/* brcl 0,0 */
+	/* brcl 0,offset */
 	insn->opcode = 0xc004;
-	insn->offset = 0;
+	insn->offset = (jump_entry_target(entry) - jump_entry_code(entry)) >> 1;
 }
 
 static void jump_label_make_branch(struct jump_entry *entry, struct insn *insn)
@@ -77,23 +77,15 @@ static void __jump_label_transform(struct jump_entry *entry,
 	s390_kernel_write(code, &new, sizeof(new));
 }
 
-static int __sm_arch_jump_label_transform(void *data)
+static void __jump_label_sync(void *dummy)
 {
-	struct insn_args *args = data;
-
-	__jump_label_transform(args->entry, args->type, 0);
-	return 0;
 }
 
 void arch_jump_label_transform(struct jump_entry *entry,
 			       enum jump_label_type type)
 {
-	struct insn_args args;
-
-	args.entry = entry;
-	args.type = type;
-
-	stop_machine_cpuslocked(__sm_arch_jump_label_transform, &args, NULL);
+	__jump_label_transform(entry, type, 0);
+	smp_call_function(__jump_label_sync, NULL, 1);
 }
 
 void arch_jump_label_transform_static(struct jump_entry *entry,

arch/s390/mm/maccess.c

@@ -52,21 +52,22 @@ static notrace long s390_kernel_write_odd(void *dst, const void *src, size_t siz
  * Therefore we have a read-modify-write sequence: the function reads eight
  * bytes from destination at an eight byte boundary, modifies the bytes
  * requested and writes the result back in a loop.
- *
- * Note: this means that this function may not be called concurrently on
- *	 several cpus with overlapping words, since this may potentially
- *	 cause data corruption.
  */
+static DEFINE_SPINLOCK(s390_kernel_write_lock);
+
 void notrace s390_kernel_write(void *dst, const void *src, size_t size)
 {
+	unsigned long flags;
 	long copied;
 
+	spin_lock_irqsave(&s390_kernel_write_lock, flags);
 	while (size) {
 		copied = s390_kernel_write_odd(dst, src, size);
 		dst += copied;
 		src += copied;
 		size -= copied;
 	}
+	spin_unlock_irqrestore(&s390_kernel_write_lock, flags);
 }
 
 static int __memcpy_real(void *dest, void *src, size_t count)