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[34.16.141.147]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-734d444a9fasm7386454b3a.60.2025.03.03.14.17.02 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 03 Mar 2025 14:17:03 -0800 (PST) Date: Mon, 3 Mar 2025 22:16:57 +0000 From: Peilin Ye To: Alexei Starovoitov Cc: bpf@vger.kernel.org, linux-arm-kernel@lists.infradead.org, oe-kbuild-all@lists.linux.dev, bpf@ietf.org, Alexei Starovoitov , Xu Kuohai , Eduard Zingerman , David Vernet , Daniel Borkmann , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Jonathan Corbet , "Paul E. McKenney" , Puranjay Mohan , Ilya Leoshkevich , Heiko Carstens , Vasily Gorbik , Catalin Marinas , Will Deacon , Quentin Monnet , Mykola Lysenko , Shuah Khan , Ihor Solodrai Subject: Re: [PATCH bpf-next v4 04/10] bpf: Introduce load-acquire and store-release instructions Message-ID: References: <2c82b29f3530b961b41f94a4942e490ab35a31c8.1740978603.git.yepeilin@google.com> <202503031631.OeUhVRHz-lkp@intel.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Mar 03, 2025 at 10:43:07AM -0800, Alexei Starovoitov wrote: > > compiler: arc-elf-gcc (GCC) 13.2.0 > > ... > > > kernel/bpf/core.c:2228:25: note: in expansion of macro 'LOAD_ACQUIRE' > > 2228 | LOAD_ACQUIRE(DW, u64) > > | ^~~~~~~~~~~~ *facepalm* > Peilin, > > how do you plan on fixing this? > So far I could only think of making compilation conditional for CONFIG_64BIT > and let the verifier reject these insns on 32-bit arches. Agreed - after searching for "Need native word sized stores/loads for atomicity." on lore, it appears that we can't have 64-bit smp_{load_acquire,store_release}() on 32-bit arches. My draft fix is: diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 323af18d7d49..6df1d3e379a4 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -2225,7 +2225,9 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) LOAD_ACQUIRE(B, u8) LOAD_ACQUIRE(H, u16) LOAD_ACQUIRE(W, u32) +#ifdef CONFIG_64BIT LOAD_ACQUIRE(DW, u64) +#endif #undef LOAD_ACQUIRE default: goto default_label; @@ -2241,7 +2243,9 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) STORE_RELEASE(B, u8) STORE_RELEASE(H, u16) STORE_RELEASE(W, u32) +#ifdef CONFIG_64BIT STORE_RELEASE(DW, u64) +#endif #undef STORE_RELEASE default: goto default_label; diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index dac7af73ac8a..d0e4c6bab37d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -7814,8 +7814,16 @@ static int check_atomic(struct bpf_verifier_env *env, struct bpf_insn *insn) case BPF_CMPXCHG: return check_atomic_rmw(env, insn); case BPF_LOAD_ACQ: + if (BPF_SIZE(insn->code) == BPF_DW && BITS_PER_LONG != 64) { + verbose(env, "64-bit load-acquire is only supported on 64-bit arches\n"); + return -ENOTSUPP; + } return check_atomic_load(env, insn); case BPF_STORE_REL: + if (BPF_SIZE(insn->code) == BPF_DW && BITS_PER_LONG != 64) { + verbose(env, "64-bit store-release is only supported on 64-bit arches\n"); + return -ENOTSUPP; + } return check_atomic_store(env, insn); default: verbose(env, "BPF_ATOMIC uses invalid atomic opcode %02x\n", Thanks, Peilin Ye