linux-kernel - Re: [PATCH bpf-next] bpf,x86: do RSB balance for trampoline

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Message-ID: <CAADnVQKQ2Pqhb9wNjRuEP5AoGc6-MfLhQLD++gQPf3VB_rV+fQ@mail.gmail.com>
Date: Mon, 10 Nov 2025 08:32:29 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Menglong Dong <menglong.dong@...ux.dev>
Cc: sjenning@...hat.com, Peter Zijlstra <peterz@...radead.org>, 
	Menglong Dong <menglong8.dong@...il.com>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eduard <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, "David S. Miller" <davem@...emloft.net>, David Ahern <dsahern@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, X86 ML <x86@...nel.org>, 
	"H. Peter Anvin" <hpa@...or.com>, jiang.biao@...ux.dev, bpf <bpf@...r.kernel.org>, 
	Network Development <netdev@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH bpf-next] bpf,x86: do RSB balance for trampoline

On Mon, Nov 10, 2025 at 3:43 AM Menglong Dong <menglong.dong@...ux.dev> wrote:
>
>
> Do you think if it is worth to implement the livepatch with
> bpf trampoline by introduce the CONFIG_LIVEPATCH_BPF?
> It's easy to achieve it, I have a POC for it, and the performance
> of the livepatch increase from 99M/s to 200M/s according to
> my bench testing.

what do you mean exactly?
I don't want to add more complexity to bpf trampoline.
Improve current livepatching logic ? jmp vs call isn't special.

> The results above is tested with return-trunk disabled. With the
> return-trunk enabled, the performance decrease from 58M/s to
> 52M/s. The main performance improvement comes from the RSB,
> and the return-trunk will always break the RSB, which makes it has
> no improvement. The calling to per-cpu-ref get and put make
> the bpf trampoline based livepatch has a worse performance
> than ftrace based.
>
> Thanks!
> Menglong Dong
>
> >
>
>
>
>