s390/maccess: remove potentially broken probe_kernel_write()

Remove the s390 architecture implementation of probe_kernel_write() and
instead use a new function s390_kernel_write() to modify kernel text and
data everywhere.

The s390 implementation of probe_kernel_write() was potentially broken
since it modified memory in a read-modify-write fashion, which read four
bytes, modified the requested bytes within those four bytes and wrote
the result back.
If two cpus would modify the same four byte area at different locations
within that area, this could lead to corruption.
Right now the only places which called probe_kernel_write() did run within
stop_machine_run. Therefore the scenario can't happen right now, however
that might change at any time.

To fix this rename probe_kernel_write() to s390_kernel_write() which can
have special semantics, like only call it while running within stop_machine().

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/ftrace.c

@@ -130,8 +130,7 @@ int ftrace_make_nop(struct module *mod, struct dyn_ftrace *rec,
 	/* Verify that the to be replaced code matches what we expect. */
 	if (memcmp(&orig, &old, sizeof(old)))
 		return -EINVAL;
-	if (probe_kernel_write((void *) rec->ip, &new, sizeof(new)))
-		return -EPERM;
+	s390_kernel_write((void *) rec->ip, &new, sizeof(new));
 	return 0;
 }
 
@@ -159,8 +158,7 @@ int ftrace_make_call(struct dyn_ftrace *rec, unsigned long addr)
 	/* Verify that the to be replaced code matches what we expect. */
 	if (memcmp(&orig, &old, sizeof(old)))
 		return -EINVAL;
-	if (probe_kernel_write((void *) rec->ip, &new, sizeof(new)))
-		return -EPERM;
+	s390_kernel_write((void *) rec->ip, &new, sizeof(new));
 	return 0;
 }
 
@@ -231,14 +229,16 @@ int ftrace_enable_ftrace_graph_caller(void)
 {
 	u8 op = 0x04; /* set mask field to zero */
 
-	return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
+	s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
+	return 0;
 }
 
 int ftrace_disable_ftrace_graph_caller(void)
 {
 	u8 op = 0xf4; /* set mask field to all ones */
 
-	return probe_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
+	s390_kernel_write(__va(ftrace_graph_caller)+1, &op, sizeof(op));
+	return 0;
 }
 
 #endif /* CONFIG_FUNCTION_GRAPH_TRACER */