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([38.34.87.7]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-72dab816412sm11055732b3a.66.2025.01.22.04.05.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 22 Jan 2025 04:05:05 -0800 (PST) From: Eduard Zingerman To: bpf@vger.kernel.org, ast@kernel.org Cc: andrii@kernel.org, daniel@iogearbox.net, martin.lau@linux.dev, kernel-team@fb.com, yonghong.song@linux.dev, Eduard Zingerman Subject: [RFC bpf-next v1 6/7] bpf: use register liveness information for func_states_equal Date: Wed, 22 Jan 2025 04:04:41 -0800 Message-ID: <20250122120442.3536298-7-eddyz87@gmail.com> X-Mailer: git-send-email 2.47.1 In-Reply-To: <20250122120442.3536298-1-eddyz87@gmail.com> References: <20250122120442.3536298-1-eddyz87@gmail.com> Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Liveness analysis DFA computes a set of registers live before each instruction. Leverage this information to skip comparison of dead registers in func_states_equal(). This helps with convergance of iterator processing loops, as bpf_reg_state->live marks can't be used when loops are processed. This has certain performance impact for selftests, here is a veristat listing for bigger ones (this patch compared to previous patch): File Program Insns (DIFF) States (DIFF) -------------------- -------------------------- --------------- -------------- iters.bpf.o checkpoint_states_deletion -8617 (-87.68%) -327 (-89.10%) iters.bpf.o iter_nested_iters -140 (-18.13%) -10 (-13.89%) pyperf600_iter.bpf.o on_event -2608 (-41.31%) -29 (-10.32%) Impact on sched_ext: Program Insns (DIFF) States (DIFF) ---------------------- ---------------- --------------- lavd_dispatch -34018 (-22.00%) -1885 (-21.06%) layered_dispatch -1808 (-22.83%) -86 (-13.85%) layered_dump -943 (-20.17%) -44 (-16.30%) layered_init -995 (-18.05%) -80 (-15.41%) refresh_layer_cpumasks -395 (-30.74%) -34 (-28.33%) rustland_init -63 (-13.24%) -3 (-8.11%) rustland_init -63 (-13.24%) -3 (-8.11%) tp_cgroup_attach_task -53 (-26.24%) -4 (-22.22%) central_init -146 (-25.09%) -2 (-5.26%) pair_dispatch -331 (-17.34%) -15 (-10.56%) qmap_dispatch -375 (-17.15%) -26 (-14.94%) userland_dispatch -34 (-21.79%) -4 (-23.53%) Signed-off-by: Eduard Zingerman --- kernel/bpf/verifier.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index d36c5a3309e9..babc2e179c08 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -18223,15 +18223,17 @@ static bool refsafe(struct bpf_verifier_state *old, struct bpf_verifier_state *c * the current state will reach 'bpf_exit' instruction safely */ static bool func_states_equal(struct bpf_verifier_env *env, struct bpf_func_state *old, - struct bpf_func_state *cur, enum exact_level exact) + struct bpf_func_state *cur, u32 insn_idx, enum exact_level exact) { - int i; + u16 live_regs = env->insn_aux_data[insn_idx].live_regs_before; + u16 i; if (old->callback_depth > cur->callback_depth) return false; for (i = 0; i < MAX_BPF_REG; i++) - if (!regsafe(env, &old->regs[i], &cur->regs[i], + if (((1 << i) & live_regs) && + !regsafe(env, &old->regs[i], &cur->regs[i], &env->idmap_scratch, exact)) return false; @@ -18252,6 +18254,7 @@ static bool states_equal(struct bpf_verifier_env *env, struct bpf_verifier_state *cur, enum exact_level exact) { + u32 insn_idx; int i; if (old->curframe != cur->curframe) @@ -18275,9 +18278,12 @@ static bool states_equal(struct bpf_verifier_env *env, * and all frame states need to be equivalent */ for (i = 0; i <= old->curframe; i++) { + insn_idx = i == old->curframe + ? env->insn_idx + : old->frame[i + 1]->callsite; if (old->frame[i]->callsite != cur->frame[i]->callsite) return false; - if (!func_states_equal(env, old->frame[i], cur->frame[i], exact)) + if (!func_states_equal(env, old->frame[i], cur->frame[i], insn_idx, exact)) return false; } return true; -- 2.47.1