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From:   Pu Lehui <pulehui@huaweicloud.com>
To:     bpf@vger.kernel.org, linux-riscv@lists.infradead.org,
        linux-kernel@vger.kernel.org
Cc:     =?UTF-8?q?Bj=C3=B6rn=20T=C3=B6pel?= <bjorn@kernel.org>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Andrii Nakryiko <andrii@kernel.org>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>, Yonghong Song <yhs@fb.com>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Pu Lehui <pulehui@huawei.com>,
        Pu Lehui <pulehui@huaweicloud.com>
Subject: [RFC PATCH bpf-next 1/4] bpf: Rollback to text_poke when arch not supported ftrace direct call
Date:   Mon, 19 Dec 2022 21:37:33 +0800
Message-Id: <20221219133736.1387008-2-pulehui@huaweicloud.com>
In-Reply-To: <20221219133736.1387008-1-pulehui@huaweicloud.com>
References: <20221219133736.1387008-1-pulehui@huaweicloud.com>
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From: Pu Lehui <pulehui@huawei.com>

The current bpf trampoline attach to kernel functions via ftrace direct
call API, while text_poke is applied for bpf2bpf attach and tail call
optimization. For architectures that do not support ftrace direct call,
text_poke is still able to attach bpf trampoline to kernel functions.
Let's relax it by rollback to text_poke when architecture not supported.

Signed-off-by: Pu Lehui <pulehui@huawei.com>
---
 kernel/bpf/trampoline.c | 8 ++------
 1 file changed, 2 insertions(+), 6 deletions(-)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index d6395215b849..386197a7952c 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -228,15 +228,11 @@ static int modify_fentry(struct bpf_trampoline *tr, void *old_addr, void *new_ad
 static int register_fentry(struct bpf_trampoline *tr, void *new_addr)
 {
 	void *ip = tr->func.addr;
-	unsigned long faddr;
 	int ret;
 
-	faddr = ftrace_location((unsigned long)ip);
-	if (faddr) {
-		if (!tr->fops)
-			return -ENOTSUPP;
+	if (IS_ENABLED(CONFIG_DYNAMIC_FTRACE_WITH_DIRECT_CALLS) &&
+	    !!ftrace_location((unsigned long)ip))
 		tr->func.ftrace_managed = true;
-	}
 
 	if (bpf_trampoline_module_get(tr))
 		return -ENOENT;
-- 
2.25.1