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Wed, 21 Oct 2026 10:11:44 -0700 (PDT) Received: from localhost ([153.61.198.241]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2ea3b43478csm14601635ad.28.2026.10.21.10.11.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 Oct 2026 10:11:43 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Wed, 21 Oct 2026 17:11:42 +0000 Message-Id: Cc: "John Fastabend" , "Martin KaFai Lau" , "Song Liu" , "Yonghong Song" , "Jiri Olsa" , "Emil Tsalapatis" , "Ihor Solodrai" , "Quentin Monnet" , "Puranjay Mohan" , "Xu Kuohai" , =?utf-8?q?Bj=C3=B6rn_T=C3=B6pel?= , "Pu Lehui" , "Catalin Marinas" , "Will Deacon" , "Mark Rutland" , , , "Shahab Vahedi" , "Russell King" , "Tiezhu Yang" , "Hengqi Chen" , "Johan Almbladh" , "Paul Burton" , "James E.J. Bottomley" , "Helge Deller" , "Hari Bathini" , "Christophe Leroy (CS GROUP)" , "Naveen N Rao" , "Luke Nelson" , "Xi Wang" , "Ilya Leoshkevich" , "Heiko Carstens" , "Vasily Gorbik" , "David S. Miller" , "Wang YanQing" , "Jakub Kicinski" , "Jonathan Corbet" , , "Tianci Cao" , "Yazhou Tang" , "Shenghao Yuan" Subject: Re: [PATCH bpf-next v2 1/8] bpf: Add UHMUL and SHMUL instructions From: "Alexei Starovoitov" To: , , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" , "David Vernet" , In-Reply-To: <20261021-bpf-hmul-v2-1-88e260099f7d@outlook.com> References: <20261021-bpf-hmul-v2-0-88e260099f7d@outlook.com> <20261021-bpf-hmul-v2-1-88e260099f7d@outlook.com> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit X-Mailing-List: linux-doc@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 On Tue, Oct 20, 2026 at 10:40 PM tangyazhou@zju.edu.cn wrote: > +static inline bool bpf_insn_is_hmul(const struct bpf_insn *insn) > +{ > + return BPF_CLASS(insn->code) == BPF_ALU64 && > + BPF_OP(insn->code) == BPF_MUL && > + bpf_is_hmul_variant(insn->off); > +} Patch 5 adds this check to 13 JITs and nfp to opt them out. Lets make JITs opt in instead, like bpf_jit_supports_callx(). The verifier checks it once. x86, arm64 and riscv patches add bpf_jit_supports_hmul() that returns true. bpf_prog_is_offloaded() covers nfp. When JIT is on and it doesn't support them the prog is rejected with a message in the log instead of silent fallback to the interpreter. Then patch 5 goes away and only arm64 and riscv acks are needed. Like: diff --git a/include/linux/filter.h b/include/linux/filter.h index e0218e6..6ee8d1a 100644 --- a/include/linux/filter.h +++ b/include/linux/filter.h @@ -152,6 +152,13 @@ struct ctl_table_header; #define BPF_ALU32_IMM(OP, DST, IMM) \ BPF_ALU32_IMM_OFF(OP, DST, IMM, 0) +static inline bool bpf_insn_is_hmul(const struct bpf_insn *insn) +{ + return BPF_CLASS(insn->code) == BPF_ALU64 && + BPF_OP(insn->code) == BPF_MUL && + (insn->off == BPF_UHMUL || insn->off == BPF_SHMUL); +} + /* Endianess conversion, cpu_to_{l,b}e(), {l,b}e_to_cpu() */ #define BPF_ENDIAN(TYPE, DST, LEN) \ @@ -1281,6 +1288,7 @@ bool bpf_jit_supports_kfunc_call(void); bool bpf_jit_supports_callx(void); bool bpf_jit_supports_kfunc_ret_reg_pair(void); bool bpf_jit_supports_unwind(void); +bool bpf_jit_supports_hmul(void); bool bpf_jit_supports_stack_args(void); bool bpf_jit_supports_arena_args(void); bool bpf_jit_supports_far_kfunc_call(void); diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h index f29b0aa..90c30e5 100644 --- a/include/uapi/linux/bpf.h +++ b/include/uapi/linux/bpf.h @@ -34,6 +34,12 @@ #define BPF_FROM_LE BPF_TO_LE #define BPF_FROM_BE BPF_TO_BE +/* BPF_MUL off values for high-half multiplication; BPF_ALU64 only. */ +enum bpf_mul_variant { + BPF_UHMUL = 1, + BPF_SHMUL = 2, +}; + /* jmp encodings */ #define BPF_JNE 0x50 /* jump != */ #define BPF_JLT 0xa0 /* LT is unsigned, '<' */ diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index 3030beb..e17704a 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -3405,6 +3405,12 @@ bool __weak bpf_jit_supports_unwind(void) return false; } +/* uhmul and shmul */ +bool __weak bpf_jit_supports_hmul(void) +{ + return false; +} + /* * How this arch places a by-value kfunc argument, or NULL for one that has * not opted in and so only takes an argument of a single eightbyte, which diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 5601d20..9a3c97d 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -21194,6 +21194,17 @@ static int fd_array_get_map_idx(struct bpf_verifier_env *env, u32 idx) return -EPROTO; } +/* The interpreter supports uhmul and shmul. JITs opt in. */ +static int check_hmul_jit(struct bpf_verifier_env *env) +{ + if (bpf_prog_is_offloaded(env->prog->aux) || + (env->prog->jit_requested && !bpf_jit_supports_hmul())) { + verbose(env, "JIT doesn't support uhmul and shmul\n"); + return -EOPNOTSUPP; + } + return 0; +} + static int check_alu_fields(struct bpf_verifier_env *env, struct bpf_insn *insn) { u8 class = BPF_CLASS(insn->code); @@ -21249,6 +21260,13 @@ static int check_alu_fields(struct bpf_verifier_env *env, struct bpf_insn *insn) case BPF_MUL: case BPF_DIV: case BPF_MOD: + if (bpf_insn_is_hmul(insn)) { + if (BPF_SRC(insn->code) == BPF_X ? insn->imm : insn->src_reg) { + verbose(env, "BPF_ALU uses reserved fields\n"); + return -EINVAL; + } + return check_hmul_jit(env); + } if (BPF_SRC(insn->code) == BPF_X) { if (insn->imm != 0 || (insn->off != 0 && insn->off != 1) || (insn->off == 1 && opcode != BPF_MOD && opcode != BPF_DIV)) { pw-bot: cr