netdev - [PATCH bpf-next v2 2/2] bpf: Make BPF_JIT_DEFAULT

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Date:   Sat, 19 Feb 2022 11:15:02 +0800
From:   Tiezhu Yang <yangtiezhu@...ngson.cn>
To:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        John Fastabend <john.fastabend@...il.com>,
        KP Singh <kpsingh@...nel.org>
Cc:     Xuefeng Li <lixuefeng@...ngson.cn>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v2 2/2] bpf: Make BPF_JIT_DEFAULT_ON selectable in Kconfig

Currently, only x86, arm64 and s390 select ARCH_WANT_DEFAULT_BPF_JIT,
the other archs do not select ARCH_WANT_DEFAULT_BPF_JIT. On the archs
without ARCH_WANT_DEFAULT_BPF_JIT, if we want to set bpf_jit_enable to
1 by default, the only way is to enable CONFIG_BPF_JIT_ALWAYS_ON, then
the users can not change it to 0 or 2, it seems bad for some users. We
can select ARCH_WANT_DEFAULT_BPF_JIT for those archs if it is proper,
but at least for now, make BPF_JIT_DEFAULT_ON selectable can give them
a chance.

Additionally, with this patch, under !BPF_JIT_ALWAYS_ON, we can disable
BPF_JIT_DEFAULT_ON on the archs with ARCH_WANT_DEFAULT_BPF_JIT when make
menuconfig, it seems flexible for some developers.

Signed-off-by: Tiezhu Yang <yangtiezhu@...ngson.cn>
---
 kernel/bpf/Kconfig | 13 +++++++++++--
 1 file changed, 11 insertions(+), 2 deletions(-)

diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
index cbf3f65..461ac60 100644
--- a/kernel/bpf/Kconfig
+++ b/kernel/bpf/Kconfig
@@ -54,6 +54,7 @@ config BPF_JIT
 config BPF_JIT_ALWAYS_ON
 	bool "Permanently enable BPF JIT and remove BPF interpreter"
 	depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
+	select BPF_JIT_DEFAULT_ON
 	help
 	  Enables BPF JIT and removes BPF interpreter to avoid speculative
 	  execution of BPF instructions by the interpreter.
@@ -63,8 +64,16 @@ config BPF_JIT_ALWAYS_ON
 	  in failure.
 
 config BPF_JIT_DEFAULT_ON
-	def_bool ARCH_WANT_DEFAULT_BPF_JIT || BPF_JIT_ALWAYS_ON
-	depends on HAVE_EBPF_JIT && BPF_JIT
+	bool "Defaultly enable BPF JIT and remove BPF interpreter"
+	default y if ARCH_WANT_DEFAULT_BPF_JIT
+	depends on BPF_SYSCALL && HAVE_EBPF_JIT && BPF_JIT
+	help
+	  Enables BPF JIT and removes BPF interpreter to avoid speculative
+	  execution of BPF instructions by the interpreter.
+
+	  When CONFIG_BPF_JIT_DEFAULT_ON is enabled but CONFIG_BPF_JIT_ALWAYS_ON
+	  is disabled, /proc/sys/net/core/bpf_jit_enable is set to 1 by default
+	  and can be changed to 0 or 2.
 
 config BPF_UNPRIV_DEFAULT_OFF
 	bool "Disable unprivileged BPF by default"
-- 
2.1.0