Re: [PATCHv5 bpf-next 9/9] bpf,x86: Use single ftrace_ops for direct calls

Jiri Olsa
2025-12-28T15:22:22Z

On Fri, Dec 19, 2025 at 10:27:56AM +0100, Jiri Olsa wrote:

> > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
> > > index 4661b9e606e0..1ad2e307c834 100644
> > > --- a/kernel/trace/Kconfig
> > > +++ b/kernel/trace/Kconfig
> > > @@ -50,6 +50,9 @@ config HAVE_DYNAMIC_FTRACE_WITH_REGS
> > > config HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> > > bool
> > >
> > > +config HAVE_SINGLE_FTRACE_DIRECT_OPS
> > > + bool
> > > +
> >
> > Now you could add:
> >
> > config SINGLE_FTRACE_DIRECT_OPS
> > bool
> > default y
> > depends on HAVE_SINGLE_FTRACE_DIRECT_OPS && DYNAMIC_FTRACE_WITH_DIRECT_CALLS
>
> ok, the dependency is more ovbvious, will change
>
> thanks,
> jirka

actualy, it seems that having it the original way with adding the rest
of the wrappers for !CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS case is
easier AFAICS

jirka

---
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 80527299f859..53bf2cf7ff6f 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -336,6 +336,7 @@ config X86
select SCHED_SMT if SMP
select ARCH_SUPPORTS_SCHED_CLUSTER if SMP
select ARCH_SUPPORTS_SCHED_MC if SMP
+ select HAVE_SINGLE_FTRACE_DIRECT_OPS if X86_64 && DYNAMIC_FTRACE_WITH_DIRECT_CALLS

config INSTRUCTION_DECODER
def_bool y
diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index e5a0d58ed6dc..a8b3f510280a 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -33,12 +33,40 @@ static DEFINE_MUTEX(trampoline_mutex);
#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mutex);

+#ifdef CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS
+static struct bpf_trampoline *direct_ops_ip_lookup(struct ftrace_ops *ops, unsigned long ip)
+{
+ struct hlist_head *head_ip;
+ struct bpf_trampoline *tr;
+
+ mutex_lock(&trampoline_mutex);
+ head_ip = &trampoline_ip_table[hash_64(ip, TRAMPOLINE_HASH_BITS)];
+ hlist_for_each_entry(tr, head_ip, hlist_ip) {
+ if (tr->ip == ip)
+ goto out;
+ }
+ tr = NULL;
+out:
+ mutex_unlock(&trampoline_mutex);
+ return tr;
+}
+#else
+static struct bpf_trampoline *direct_ops_ip_lookup(struct ftrace_ops *ops, unsigned long ip)
+{
+ return ops->private;
+}
+#endif /* CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS */
+
static int bpf_tramp_ftrace_ops_func(struct ftrace_ops *ops, unsigned long ip,
enum ftrace_ops_cmd cmd)
{
- struct bpf_trampoline *tr = ops->private;
+ struct bpf_trampoline *tr;
int ret = 0;

+ tr = direct_ops_ip_lookup(ops, ip);
+ if (!tr)
+ return -EINVAL;
+
if (cmd == FTRACE_OPS_CMD_ENABLE_SHARE_IPMODIFY_SELF) {
/* This is called inside register_ftrace_direct_multi(), so
* tr->mutex is already locked.
@@ -137,6 +165,159 @@ void bpf_image_ksym_del(struct bpf_ksym *ksym)
PAGE_SIZE, true, ksym->name);
}

+#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
+#ifdef CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS
+/*
+ * We have only single direct_ops which contains all the direct call
+ * sites and is the only global ftrace_ops for all trampolines.
+ *
+ * We use 'update_ftrace_direct_*' api for attachment.
+ */
+struct ftrace_ops direct_ops = {
+ .ops_func = bpf_tramp_ftrace_ops_func,
+};
+
+static int direct_ops_alloc(struct bpf_trampoline *tr)
+{
+ tr->fops = &direct_ops;
+ return 0;
+}
+
+static void direct_ops_free(struct bpf_trampoline *tr) { }
+
+static struct ftrace_hash *hash_from_ip(struct bpf_trampoline *tr, void *ptr)
+{
+ unsigned long ip, addr = (unsigned long) ptr;
+ struct ftrace_hash *hash;
+
+ ip = ftrace_location(tr->ip);
+ if (!ip)
+ return NULL;
+ hash = alloc_ftrace_hash(FTRACE_HASH_DEFAULT_BITS);
+ if (!hash)
+ return NULL;
+ if (bpf_trampoline_use_jmp(tr->flags))
+ addr = ftrace_jmp_set(addr);
+ if (!add_ftrace_hash_entry_direct(hash, ip, addr)) {
+ free_ftrace_hash(hash);
+ return NULL;
+ }
+ return hash;
+}
+
+static int direct_ops_add(struct bpf_trampoline *tr, void *addr)
+{
+ struct ftrace_hash *hash = hash_from_ip(tr, addr);
+ int err = -ENOMEM;
+
+ if (hash)
+ err = update_ftrace_direct_add(tr->fops, hash);
+ free_ftrace_hash(hash);
+ return err;
+}
+
+static int direct_ops_del(struct bpf_trampoline *tr, void *addr)
+{
+ struct ftrace_hash *hash = hash_from_ip(tr, addr);
+ int err = -ENOMEM;
+
+ if (hash)
+ err = update_ftrace_direct_del(tr->fops, hash);
+ free_ftrace_hash(hash);
+ return err;
+}
+
+static int direct_ops_mod(struct bpf_trampoline *tr, void *addr, bool lock_direct_mutex)
+{
+ struct ftrace_hash *hash = hash_from_ip(tr, addr);
+ int err = -ENOMEM;
+
+ if (hash)
+ err = update_ftrace_direct_mod(tr->fops, hash, lock_direct_mutex);
+ free_ftrace_hash(hash);
+ return err;
+}
+#else
+/*
+ * We allocate ftrace_ops object for each trampoline and it contains
+ * call site specific for that trampoline.
+ *
+ * We use *_ftrace_direct api for attachment.
+ */
+static int direct_ops_alloc(struct bpf_trampoline *tr)
+{
+ tr->fops = kzalloc(sizeof(struct ftrace_ops), GFP_KERNEL);
+ if (!tr->fops)
+ return -ENOMEM;
+ tr->fops->private = tr;
+ tr->fops->ops_func = bpf_tramp_ftrace_ops_func;
+ return 0;
+}
+
+static void direct_ops_free(struct bpf_trampoline *tr)
+{
+ if (tr->fops) {
+ ftrace_free_filter(tr->fops);
+ kfree(tr->fops);
+ }
+}
+
+static int direct_ops_add(struct bpf_trampoline *tr, void *ptr)
+{
+ unsigned long addr = (unsigned long) ptr;
+ struct ftrace_ops *ops = tr->fops;
+ int ret;
+
+ if (bpf_trampoline_use_jmp(tr->flags))
+ addr = ftrace_jmp_set(addr);
+
+ ret = ftrace_set_filter_ip(ops, tr->ip, 0, 1);
+ if (ret)
+ return ret;
+ return register_ftrace_direct(ops, addr);
+}
+
+static int direct_ops_del(struct bpf_trampoline *tr, void *addr)
+{
+ return unregister_ftrace_direct(tr->fops, (long)addr, false);
+}
+
+static int direct_ops_mod(struct bpf_trampoline *tr, void *ptr, bool lock_direct_mutex)
+{
+ unsigned long addr = (unsigned long) ptr;
+ struct ftrace_ops *ops = tr->fops;
+
+ if (bpf_trampoline_use_jmp(tr->flags))
+ addr = ftrace_jmp_set(addr);
+ if (lock_direct_mutex)
+ return modify_ftrace_direct(ops, addr);
+ return modify_ftrace_direct_nolock(ops, addr);
+}
+#endif /* CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS */
+#else
+static void direct_ops_free(struct bpf_trampoline *tr) { }
+
+static int direct_ops_alloc(struct bpf_trampoline *tr)
+{
+ return 0;
+}
+
+static int direct_ops_add(struct bpf_trampoline *tr, void *addr)
+{
+ return -ENODEV;
+}
+
+static int direct_ops_del(struct bpf_trampoline *tr, void *addr)
+{
+ return -ENODEV;
+}
+
+static int direct_ops_mod(struct bpf_trampoline *tr, void *ptr, bool lock_direct_mutex)
+{
+ return -ENODEV;
+}
+#endif /* CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS */
+
static struct bpf_trampoline *bpf_trampoline_lookup(u64 key, unsigned long ip)
{
struct bpf_trampoline *tr;
@@ -154,16 +335,11 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key, unsigned long ip)
tr = kzalloc(sizeof(*tr), GFP_KERNEL);
if (!tr)
goto out;
-#ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
- tr->fops = kzalloc(sizeof(struct ftrace_ops), GFP_KERNEL);
- if (!tr->fops) {
+ if (direct_ops_alloc(tr)) {
kfree(tr);
tr = NULL;
goto out;
}
- tr->fops->private = tr;
- tr->fops->ops_func = bpf_tramp_ftrace_ops_func;
-#endif

tr->key = key;
tr->ip = ftrace_location(ip);
@@ -206,7 +382,7 @@ static int unregister_fentry(struct bpf_trampoline *tr, u32 orig_flags,
int ret;

if (tr->func.ftrace_managed)
- ret = unregister_ftrace_direct(tr->fops, (long)old_addr, false);
+ ret = direct_ops_del(tr, old_addr);
else
ret = bpf_trampoline_update_fentry(tr, orig_flags, old_addr, NULL);

@@ -220,15 +396,7 @@ static int modify_fentry(struct bpf_trampoline *tr, u32 orig_flags,
int ret;

if (tr->func.ftrace_managed) {
- unsigned long addr = (unsigned long) new_addr;
-
- if (bpf_trampoline_use_jmp(tr->flags))
- addr = ftrace_jmp_set(addr);
-
- if (lock_direct_mutex)
- ret = modify_ftrace_direct(tr->fops, addr);
- else
- ret = modify_ftrace_direct_nolock(tr->fops, addr);
+ ret = direct_ops_mod(tr, new_addr, lock_direct_mutex);
} else {
ret = bpf_trampoline_update_fentry(tr, orig_flags, old_addr,
new_addr);
@@ -251,15 +419,7 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
}

if (tr->func.ftrace_managed) {
- unsigned long addr = (unsigned long) new_addr;
-
- if (bpf_trampoline_use_jmp(tr->flags))
- addr = ftrace_jmp_set(addr);
-
- ret = ftrace_set_filter_ip(tr->fops, (unsigned long)ip, 0, 1);
- if (ret)
- return ret;
- ret = register_ftrace_direct(tr->fops, addr);
+ ret = direct_ops_add(tr, new_addr);
} else {
ret = bpf_trampoline_update_fentry(tr, 0, NULL, new_addr);
}
@@ -910,10 +1070,7 @@ void bpf_trampoline_put(struct bpf_trampoline *tr)
*/
hlist_del(&tr->hlist_key);
hlist_del(&tr->hlist_ip);
- if (tr->fops) {
- ftrace_free_filter(tr->fops);
- kfree(tr->fops);
- }
+ direct_ops_free(tr);
kfree(tr);
out:
mutex_unlock(&trampoline_mutex);
diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
index bfa2ec46e075..d7042a09fe46 100644
--- a/kernel/trace/Kconfig
+++ b/kernel/trace/Kconfig
@@ -50,6 +50,9 @@ config HAVE_DYNAMIC_FTRACE_WITH_REGS
config HAVE_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
bool

+config HAVE_SINGLE_FTRACE_DIRECT_OPS
+ bool
+
config HAVE_DYNAMIC_FTRACE_WITH_CALL_OPS
bool

diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
index 02030f62d737..4ed910d3d00d 100644
--- a/kernel/trace/ftrace.c
+++ b/kernel/trace/ftrace.c
@@ -2631,8 +2631,13 @@ unsigned long ftrace_find_rec_direct(unsigned long ip)
static void call_direct_funcs(unsigned long ip, unsigned long pip,
struct ftrace_ops *ops, struct ftrace_regs *fregs)
{
- unsigned long addr = READ_ONCE(ops->direct_call);
+ unsigned long addr;

+#ifdef CONFIG_HAVE_SINGLE_FTRACE_DIRECT_OPS
+ addr = ftrace_find_rec_direct(ip);
+#else
+ addr = READ_ONCE(ops->direct_call);
+#endif
if (!addr)
return;