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Thu, 02 Apr 2026 02:26:50 -0700 (PDT) From: Yafang Shao To: jpoimboe@kernel.org, jikos@kernel.org, mbenes@suse.cz, pmladek@suse.com, joe.lawrence@redhat.com, rostedt@goodmis.org, mhiramat@kernel.org, mathieu.desnoyers@efficios.com, kpsingh@kernel.org, mattbobrowski@google.com, song@kernel.org, jolsa@kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, martin.lau@linux.dev, eddyz87@gmail.com, memxor@gmail.com, yonghong.song@linux.dev Cc: live-patching@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, bpf@vger.kernel.org, Yafang Shao Subject: [RFC PATCH 4/4] livepatch: Implement livepatch hybrid mode Date: Thu, 2 Apr 2026 17:26:07 +0800 Message-ID: <20260402092607.96430-5-laoar.shao@gmail.com> X-Mailer: git-send-email 2.50.1 In-Reply-To: <20260402092607.96430-1-laoar.shao@gmail.com> References: <20260402092607.96430-1-laoar.shao@gmail.com> Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Livepatching allows for rapid experimentation with new kernel features without interrupting production workloads. However, static livepatches lack the flexibility required to tune features based on task-specific attributes, such as cgroup membership, which is critical in multi-tenant k8s environments. Furthermore, hardcoding logic into a livepatch prevents dynamic adjustments based on the runtime environment. To address this, we propose a hybrid approach using BPF. Our production use case involves: 1. Deploying a Livepatch function to serve as a stable BPF hook. 2. Utilizing bpf_override_return() to dynamically modify the return value of that hook based on the current task's context. A significant challenge arises when atomic-replace is enabled. In this mode, deploying a new livepatch changes the target function's address, forcing a re-attachment of the BPF program. This re-attachment latency is unacceptable in critical paths, such as those handling networking policies. To solve this, we introduce a hybrid livepatch mode that allows specific patches to remain non-replaceable, ensuring the function address remains stable and the BPF program stays attached. Signed-off-by: Yafang Shao --- kernel/livepatch/core.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c index 04f9e84f114f..5a44154131c8 100644 --- a/kernel/livepatch/core.c +++ b/kernel/livepatch/core.c @@ -665,6 +665,8 @@ static int klp_add_nops(struct klp_patch *patch) klp_for_each_object(old_patch, old_obj) { int err; + if (!old_patch->replaceable) + continue; err = klp_add_object_nops(patch, old_obj); if (err) return err; @@ -837,6 +839,8 @@ void klp_free_replaced_patches_async(struct klp_patch *new_patch) klp_for_each_patch_safe(old_patch, tmp_patch) { if (old_patch == new_patch) return; + if (!old_patch->replaceable) + continue; klp_free_patch_async(old_patch); } } @@ -1239,6 +1243,8 @@ void klp_unpatch_replaced_patches(struct klp_patch *new_patch) if (old_patch == new_patch) return; + if (!old_patch->replaceable) + continue; old_patch->enabled = false; klp_unpatch_objects(old_patch); } -- 2.47.3