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Message-ID: <12782324.O9o76ZdvQC@7950hx>
Date: Tue, 18 Nov 2025 09:20:32 +0800
From: Menglong Dong <menglong.dong@...ux.dev>
To: ast@...nel.org, rostedt@...dmis.org,
Menglong Dong <menglong8.dong@...il.com>
Cc: daniel@...earbox.net, john.fastabend@...il.com, andrii@...nel.org,
martin.lau@...ux.dev, eddyz87@...il.com, song@...nel.org,
yonghong.song@...ux.dev, kpsingh@...nel.org, sdf@...ichev.me,
haoluo@...gle.com, jolsa@...nel.org, mhiramat@...nel.org,
mark.rutland@....com, mathieu.desnoyers@...icios.com, jiang.biao@...ux.dev,
bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-trace-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next v2 6/6] bpf: implement "jmp" mode for trampoline
On 2025/11/17 11:49, Menglong Dong wrote:
> Implement the "jmp" mode for the bpf trampoline. For the ftrace_managed
> case, we need only to set the FTRACE_OPS_FL_JMP on the tr->fops if "jmp"
> is needed.
>
> For the bpf poke case, we will check the origin poke type with the
> "origin_flags", and current poke type with "tr->flags". The function
> bpf_trampoline_update_fentry() is introduced to do the job.
>
> The "jmp" mode will only be enabled with CONFIG_DYNAMIC_FTRACE_WITH_JMP
> enabled and BPF_TRAMP_F_SHARE_IPMODIFY is not set. With
> BPF_TRAMP_F_SHARE_IPMODIFY, we need to get the origin call ip from the
> stack, so we can't use the "jmp" mode.
>
> Signed-off-by: Menglong Dong <dongml2@...natelecom.cn>
> ---
> v2:
> - rename bpf_text_poke to bpf_trampoline_update_fentry
> - remove the BPF_TRAMP_F_JMPED and check the current mode with the origin
> flags instead.
> ---
> kernel/bpf/trampoline.c | 68 ++++++++++++++++++++++++++++++-----------
> 1 file changed, 51 insertions(+), 17 deletions(-)
>
> diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
> index 2dcc999a411f..80ab435d6e00 100644
> --- a/kernel/bpf/trampoline.c
> +++ b/kernel/bpf/trampoline.c
> @@ -175,24 +175,42 @@ static struct bpf_trampoline *bpf_trampoline_lookup(u64 key)
> return tr;
> }
>
> -static int unregister_fentry(struct bpf_trampoline *tr, void *old_addr)
> +static int bpf_trampoline_update_fentry(struct bpf_trampoline *tr, u32 orig_flags,
> + void *old_addr, void *new_addr)
> {
> + enum bpf_text_poke_type new_t = BPF_MOD_CALL, old_t = BPF_MOD_CALL;
> void *ip = tr->func.addr;
> +
> + if (!new_addr)
> + new_t = BPF_MOD_NOP;
> + else if (bpf_trampoline_use_jmp(tr->flags))
> + new_t = BPF_MOD_JUMP;
> +
> + if (!old_addr)
> + old_t = BPF_MOD_NOP;
> + else if (bpf_trampoline_use_jmp(orig_flags))
> + old_t = BPF_MOD_JUMP;
> +
> + return bpf_arch_text_poke(ip, old_t, new_t, old_addr, new_addr);
> +}
> +
> +static int unregister_fentry(struct bpf_trampoline *tr, u32 orig_flags,
> + void *old_addr)
> +{
> int ret;
>
> if (tr->func.ftrace_managed)
> ret = unregister_ftrace_direct(tr->fops, (long)old_addr, false);
> else
> - ret = bpf_arch_text_poke(ip, BPF_MOD_CALL, BPF_MOD_NOP,
> - old_addr, NULL);
> + ret = bpf_trampoline_update_fentry(tr, orig_flags, old_addr, NULL);
>
> return ret;
> }
>
> -static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_addr,
> +static int modify_fentry(struct bpf_trampoline *tr, u32 orig_flags,
> + void *old_addr, void *new_addr,
> bool lock_direct_mutex)
> {
> - void *ip = tr->func.addr;
> int ret;
>
> if (tr->func.ftrace_managed) {
> @@ -201,10 +219,8 @@ static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_ad
> else
> ret = modify_ftrace_direct_nolock(tr->fops, (long)new_addr);
> } else {
> - ret = bpf_arch_text_poke(ip,
> - old_addr ? BPF_MOD_CALL : BPF_MOD_NOP,
> - new_addr ? BPF_MOD_CALL : BPF_MOD_NOP,
> - old_addr, new_addr);
> + ret = bpf_trampoline_update_fentry(tr, orig_flags, old_addr,
> + new_addr);
> }
> return ret;
> }
> @@ -229,8 +245,7 @@ static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
> return ret;
> ret = register_ftrace_direct(tr->fops, (long)new_addr);
> } else {
> - ret = bpf_arch_text_poke(ip, BPF_MOD_NOP, BPF_MOD_CALL,
> - NULL, new_addr);
> + ret = bpf_trampoline_update_fentry(tr, 0, NULL, new_addr);
> }
>
> return ret;
> @@ -416,7 +431,7 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
> return PTR_ERR(tlinks);
>
> if (total == 0) {
> - err = unregister_fentry(tr, tr->cur_image->image);
> + err = unregister_fentry(tr, orig_flags, tr->cur_image->image);
> bpf_tramp_image_put(tr->cur_image);
> tr->cur_image = NULL;
> goto out;
> @@ -440,9 +455,17 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
>
> #ifdef CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS
> again:
> - if ((tr->flags & BPF_TRAMP_F_SHARE_IPMODIFY) &&
> - (tr->flags & BPF_TRAMP_F_CALL_ORIG))
> - tr->flags |= BPF_TRAMP_F_ORIG_STACK;
> + if (tr->flags & BPF_TRAMP_F_CALL_ORIG) {
> + if (tr->flags & BPF_TRAMP_F_SHARE_IPMODIFY) {
> + tr->flags |= BPF_TRAMP_F_ORIG_STACK;
> + } else if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_JMP)) {
> + /* Use "jmp" instead of "call" for the trampoline
> + * in the origin call case, and we don't need to
> + * skip the frame.
> + */
> + tr->flags &= ~BPF_TRAMP_F_SKIP_FRAME;
> + }
> + }
> #endif
>
> size = arch_bpf_trampoline_size(&tr->func.model, tr->flags,
> @@ -473,10 +496,16 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
> if (err)
> goto out_free;
>
> + if (bpf_trampoline_use_jmp(tr->flags))
> + tr->fops->flags |= FTRACE_OPS_FL_JMP;
> + else
> + tr->fops->flags &= ~FTRACE_OPS_FL_JMP;
This should be wrapped by "#ifdef CONFIG_DYNAMIC_FTRACE_WITH_JMP".
I'll change it in v3 after more human comments.
> +
> WARN_ON(tr->cur_image && total == 0);
> if (tr->cur_image)
> /* progs already running at this address */
> - err = modify_fentry(tr, tr->cur_image->image, im->image, lock_direct_mutex);
> + err = modify_fentry(tr, orig_flags, tr->cur_image->image,
> + im->image, lock_direct_mutex);
> else
> /* first time registering */
> err = register_fentry(tr, im->image);
> @@ -499,8 +528,13 @@ static int bpf_trampoline_update(struct bpf_trampoline *tr, bool lock_direct_mut
> tr->cur_image = im;
> out:
> /* If any error happens, restore previous flags */
> - if (err)
> + if (err) {
> tr->flags = orig_flags;
> + if (bpf_trampoline_use_jmp(tr->flags))
> + tr->fops->flags |= FTRACE_OPS_FL_JMP;
> + else
> + tr->fops->flags &= ~FTRACE_OPS_FL_JMP;
> + }
> kfree(tlinks);
> return err;
>
>
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