From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH net] bpf: fix liveness marking Date: Sat, 07 Oct 2017 23:29:11 +0100 (WEST) Message-ID: <20171007.232911.831489164694199337.davem@davemloft.net> References: <20171005232056.2234669-1-ast@fb.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: daniel@iogearbox.net, ecree@solarflare.com, netdev@vger.kernel.org, kernel-team@fb.com To: ast@fb.com Return-path: Received: from shards.monkeyblade.net ([184.105.139.130]:43144 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752685AbdJGW32 (ORCPT ); Sat, 7 Oct 2017 18:29:28 -0400 In-Reply-To: <20171005232056.2234669-1-ast@fb.com> Sender: netdev-owner@vger.kernel.org List-ID: From: Alexei Starovoitov Date: Thu, 5 Oct 2017 16:20:56 -0700 > while processing Rx = Ry instruction the verifier does > regs[insn->dst_reg] = regs[insn->src_reg] > which often clears write mark (when Ry doesn't have it) > that was just set by check_reg_arg(Rx) prior to the assignment. > That causes mark_reg_read() to keep marking Rx in this block as > REG_LIVE_READ (since the logic incorrectly misses that it's > screened by the write) and in many of its parents (until lucky > write into the same Rx or beginning of the program). > That causes is_state_visited() logic to miss many pruning opportunities. > > Furthermore mark_reg_read() logic propagates the read mark > for BPF_REG_FP as well (though it's readonly) which causes > harmless but unnecssary work during is_state_visited(). > Note that do_propagate_liveness() skips FP correctly, > so do the same in mark_reg_read() as well. > It saves 0.2 seconds for the test below > > program before after > bpf_lb-DLB_L3.o 2604 2304 > bpf_lb-DLB_L4.o 11159 3723 > bpf_lb-DUNKNOWN.o 1116 1110 > bpf_lxc-DDROP_ALL.o 34566 28004 > bpf_lxc-DUNKNOWN.o 53267 39026 > bpf_netdev.o 17843 16943 > bpf_overlay.o 8672 7929 > time ~11 sec ~4 sec > > Fixes: dc503a8ad984 ("bpf/verifier: track liveness for pruning") > Signed-off-by: Alexei Starovoitov Looks great, applied.