linux-kernel - Re: [PATCH v5 bpf-next 0/4] ftrace: host klp and bpf trampoline together

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Date:   Thu, 21 Jul 2022 22:59:30 +0000
From:   Song Liu <songliubraving@...com>
To:     Steven Rostedt <rostedt@...dmis.org>
CC:     bpf <bpf@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Kernel Team <Kernel-team@...com>, Jiri Olsa <jolsa@...nel.org>,
        Song Liu <song@...nel.org>
Subject: Re: [PATCH v5 bpf-next 0/4] ftrace: host klp and bpf trampoline
 together

Hi Steven, 

> On Jul 19, 2022, at 5:21 PM, Song Liu <song@...nel.org> wrote:
> 
> Changes v4 => v5:
> 1. Cleanup direct_mutex handling in register_ftrace_function.
>   (Steven Rostedt, Petr Mladek).
> 2. Various smallish fixes. (Steven Rostedt, Petr Mladek).
> 
> Changes v3 => v4:
> 1. Fix build errors for different config. (kernel test robot)
> 
> Changes v2 => v3:
> 1. Major rewrite after discussions with Steven Rostedt. [1]
> 2. Remove SHARE_IPMODIFY flag from ftrace code. Instead use the callback
>   function to communicate this information. (Steven)
> 3. Add cleanup_direct_functions_after_ipmodify() to clear SHARE_IPMODIFY
>   on the DIRECT ops when the IPMODIFY ops is removed.
> 
> Changes v1 => v2:
> 1. Fix build errors for different config. (kernel test robot)
> 
> Kernel Live Patch (livepatch, or klp) and bpf trampoline are important
> features for modern systems. This set allows the two to work on the same
> kernel function as the same time.
> 
> live patch uses ftrace with IPMODIFY, while bpf trampoline use direct
> ftrace. Existing policy does not allow the two to attach to the same kernel
> function. This is changed by fine tuning ftrace IPMODIFY policy, and allows
> one IPMODIFY ftrace_ops and one DIRECT ftrace_ops on the same kernel
> function at the same time. Please see patch 2 and 4 for more details.
> 
> Note that, one of the constraint here is to let bpf trampoline use direct
> call when it is not working on the same function as live patch. This is
> achieved by allowing ftrace code to ask bpf trampoline to make changes.
> 
> [1] https://lore.kernel.org/all/20220602193706.2607681-2-song@kernel.org/

How does this version look to you? 

Thanks,
Song