[RFC PATCH 05/14] ftrace: Add architectural helpers for [un]register_ftrace_direct()

[Naveen N. Rao]

Architectures may want to do some validation (such as to ensure that the
trampoline code is reachable from the provided ftrace location) before
accepting ftrace direct registration. Add helpers for the same.

Signed-off-by: Naveen N. Rao <naveen.n.rao at linux.vnet.ibm.com>
---
 include/linux/ftrace.h |  2 ++
 kernel/trace/ftrace.c  | 27 +++++++++++++++++++++------
 2 files changed, 23 insertions(+), 6 deletions(-)

diff --git a/include/linux/ftrace.h b/include/linux/ftrace.h
index 46b4b7ee28c41f..3fdcb4c513bc2d 100644
--- a/include/linux/ftrace.h
+++ b/include/linux/ftrace.h
@@ -290,6 +290,8 @@ int ftrace_modify_direct_caller(struct ftrace_func_entry *entry,
 				unsigned long old_addr,
 				unsigned long new_addr);
 unsigned long ftrace_find_rec_direct(unsigned long ip);
+int arch_register_ftrace_direct(unsigned long ip, unsigned long addr);
+void arch_unregister_ftrace_direct(unsigned long ip, unsigned long addr);
 #else
 # define ftrace_direct_func_count 0
 static inline int register_ftrace_direct(unsigned long ip, unsigned long addr)
diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 7476f2458b6d95..0e259b90527722 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -5005,6 +5005,13 @@ ftrace_set_addr(struct ftrace_ops *ops, unsigned long ip, int remove,
 }
 
 #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+int __weak arch_register_ftrace_direct(unsigned long ip, unsigned long addr)
+{
+	return 0;
+}
+
+void __weak arch_unregister_ftrace_direct(unsigned long ip, unsigned long addr) { }
+
 /**
  * register_ftrace_direct - Call a custom trampoline directly
  * @ip: The address of the nop at the beginning of a function
@@ -5028,6 +5035,7 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
 	struct ftrace_hash *free_hash = NULL;
 	struct dyn_ftrace *rec;
 	int ret = -EBUSY;
+	int arch_ret;
 
 	mutex_lock(&direct_mutex);
 
@@ -5082,18 +5090,24 @@ int register_ftrace_direct(unsigned long ip, unsigned long addr)
 	entry->direct = addr;
 	__add_hash_entry(direct_functions, entry);
 
-	ret = ftrace_set_filter_ip(&direct_ops, ip, 0, 0);
+	arch_ret = arch_register_ftrace_direct(ip, addr);
 
-	if (!ret && !(direct_ops.flags & FTRACE_OPS_FL_ENABLED)) {
-		ret = register_ftrace_function(&direct_ops);
-		if (ret)
-			ftrace_set_filter_ip(&direct_ops, ip, 1, 0);
+	if (!arch_ret) {
+		ret = ftrace_set_filter_ip(&direct_ops, ip, 0, 0);
+
+		if (!ret && !(direct_ops.flags & FTRACE_OPS_FL_ENABLED)) {
+			ret = register_ftrace_function(&direct_ops);
+			if (ret)
+				ftrace_set_filter_ip(&direct_ops, ip, 1, 0);
+		}
 	}
 
-	if (ret) {
+	if (arch_ret || ret) {
 		remove_hash_entry(direct_functions, entry);
 		ftrace_direct_func_count--;
 		kfree(entry);
+		if (!arch_ret)
+			arch_unregister_ftrace_direct(ip, addr);
 	}
  out_unlock:
 	mutex_unlock(&direct_mutex);
@@ -5155,6 +5169,7 @@ int unregister_ftrace_direct(unsigned long ip, unsigned long addr)
 	remove_hash_entry(direct_functions, entry);
 	ftrace_direct_func_count--;
 	kfree(entry);
+	arch_unregister_ftrace_direct(ip, addr);
  out_unlock:
 	mutex_unlock(&direct_mutex);
 
-- 
2.25.4