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[34.16.131.55]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-acec04796d6sm302970a12.55.2025.01.29.19.38.46 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Jan 2025 19:38:47 -0800 (PST) Date: Thu, 30 Jan 2025 03:38:43 +0000 From: Peilin Ye To: Alexei Starovoitov Cc: bpf , linux-arm-kernel , bpf@ietf.org, Xu Kuohai , Eduard Zingerman , David Vernet , Alexei Starovoitov , 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 , Catalin Marinas , Will Deacon , Quentin Monnet , Mykola Lysenko , Shuah Khan , Josh Don , Barret Rhoden , Neel Natu , Benjamin Segall , LKML Subject: Re: [PATCH bpf-next v1 3/8] bpf: Introduce load-acquire and store-release instructions Message-ID: References: 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: Hi Alexei, On Wed, Jan 29, 2025 at 04:41:31PM -0800, Alexei Starovoitov wrote: > > diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c > > index da729cbbaeb9..ab082ab9d535 100644 > > --- a/kernel/bpf/core.c > > +++ b/kernel/bpf/core.c > > @@ -1663,14 +1663,17 @@ EXPORT_SYMBOL_GPL(__bpf_call_base); > > INSN_3(JMP, JSET, K), \ > > INSN_2(JMP, JA), \ > > INSN_2(JMP32, JA), \ > > + /* Atomic operations. */ \ > > + INSN_3(STX, ATOMIC, B), \ > > + INSN_3(STX, ATOMIC, H), \ > > + INSN_3(STX, ATOMIC, W), \ > > + INSN_3(STX, ATOMIC, DW), \ > > /* Store instructions. */ \ > > /* Register based. */ \ > > INSN_3(STX, MEM, B), \ > > INSN_3(STX, MEM, H), \ > > INSN_3(STX, MEM, W), \ > > INSN_3(STX, MEM, DW), \ > > - INSN_3(STX, ATOMIC, W), \ > > - INSN_3(STX, ATOMIC, DW), \ > > /* Immediate based. */ \ > > INSN_3(ST, MEM, B), \ > > INSN_3(ST, MEM, H), \ > > @@ -2169,6 +2172,8 @@ static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn) > > > > STX_ATOMIC_DW: > > STX_ATOMIC_W: > > + STX_ATOMIC_H: > > + STX_ATOMIC_B: > > switch (IMM) { > > ATOMIC_ALU_OP(BPF_ADD, add) > > ATOMIC_ALU_OP(BPF_AND, and) > > STX_ATOMI_[BH] looks wrong. > It will do atomic64_*() ops in wrong size. > BPF_INSN_MAP() applies to bpf_opcode_in_insntable() > and the verifier will allow such new insns. We still have this check in check_atomic(): if (BPF_SIZE(insn->code) != BPF_W && BPF_SIZE(insn->code) != BPF_DW) { verbose(env, "invalid atomic operand size\n"); return -EINVAL; } (moved to check_atomic_rmw() in PATCH 2/8) Looks like it cannot be triggered before this patch, since STX_ATOMIC_[BH] would've already been rejected by that bpf_opcode_in_insntable() check before reaching check_atomic(). I agree that the interpreter code handling RMW atomics might now look a bit confusing though. In v2 I'll refactor that part and/or add comments to make it clearer in the code that: * only W and DW are allowed for atomic RMW * all of B, H, W and DW are allowed for atomic load/store Thanks, Peilin Ye