From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-9.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 715D4C0650F for ; Mon, 5 Aug 2019 13:23:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 41AD32087B for ; Mon, 5 Aug 2019 13:23:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565011402; bh=bVKtZbN9rtW/cD/kOWvK9wk6jF0LAT151bZvHyQi7sM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=tFzQaWfRO2t5P1OBkNH60NdQXBx1woxWcbiIibO1wT/dwaZhcvFjvFhCZh8G25oWm ShPPe2iSy8qUwct6k06fQpZseFg2KvZT/EzImdwF9MgPsNFPSbUb1LRYIjZOoTsq8w O/3qzrlq7aIgPL92ho5qT4yx973aNbgp6HLN94DM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730806AbfHENXV (ORCPT ); Mon, 5 Aug 2019 09:23:21 -0400 Received: from mail.kernel.org ([198.145.29.99]:59886 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729103AbfHENXT (ORCPT ); Mon, 5 Aug 2019 09:23:19 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id EC0DB2067D; Mon, 5 Aug 2019 13:23:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1565011398; bh=bVKtZbN9rtW/cD/kOWvK9wk6jF0LAT151bZvHyQi7sM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=jGTdrxjfXM/sjUFPhXsGYryjVsqSJaG3dY5/01eEOr/BQn6NPqGPRGbOCkjlr7p2T Hd5IJpnczSSVpg/Lgh1ghTBCnneixcSoqccuPFV3tZbk38cgFpCMOehyMoJp9R/vcY SHH510eXoJo/RhthQg6yg4IpYFCiIuYo9rgCAzhc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Randy Dunlap , Josh Poimboeuf , Thomas Gleixner , Alexei Starovoitov , "Peter Zijlstra (Intel)" , Sasha Levin Subject: [PATCH 5.2 071/131] bpf: Disable GCC -fgcse optimization for ___bpf_prog_run() Date: Mon, 5 Aug 2019 15:02:38 +0200 Message-Id: <20190805124956.311636834@linuxfoundation.org> X-Mailer: git-send-email 2.22.0 In-Reply-To: <20190805124951.453337465@linuxfoundation.org> References: <20190805124951.453337465@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ Upstream commit 3193c0836f203a91bef96d88c64cccf0be090d9c ] On x86-64, with CONFIG_RETPOLINE=n, GCC's "global common subexpression elimination" optimization results in ___bpf_prog_run()'s jumptable code changing from this: select_insn: jmp *jumptable(, %rax, 8) ... ALU64_ADD_X: ... jmp *jumptable(, %rax, 8) ALU_ADD_X: ... jmp *jumptable(, %rax, 8) to this: select_insn: mov jumptable, %r12 jmp *(%r12, %rax, 8) ... ALU64_ADD_X: ... jmp *(%r12, %rax, 8) ALU_ADD_X: ... jmp *(%r12, %rax, 8) The jumptable address is placed in a register once, at the beginning of the function. The function execution can then go through multiple indirect jumps which rely on that same register value. This has a few issues: 1) Objtool isn't smart enough to be able to track such a register value across multiple recursive indirect jumps through the jump table. 2) With CONFIG_RETPOLINE enabled, this optimization actually results in a small slowdown. I measured a ~4.7% slowdown in the test_bpf "tcpdump port 22" selftest. This slowdown is actually predicted by the GCC manual: Note: When compiling a program using computed gotos, a GCC extension, you may get better run-time performance if you disable the global common subexpression elimination pass by adding -fno-gcse to the command line. So just disable the optimization for this function. Fixes: e55a73251da3 ("bpf: Fix ORC unwinding in non-JIT BPF code") Reported-by: Randy Dunlap Signed-off-by: Josh Poimboeuf Signed-off-by: Thomas Gleixner Acked-by: Alexei Starovoitov Acked-by: Peter Zijlstra (Intel) Link: https://lkml.kernel.org/r/30c3ca29ba037afcbd860a8672eef0021addf9fe.1563413318.git.jpoimboe@redhat.com Signed-off-by: Sasha Levin --- include/linux/compiler-gcc.h | 2 ++ include/linux/compiler_types.h | 4 ++++ kernel/bpf/core.c | 2 +- 3 files changed, 7 insertions(+), 1 deletion(-) diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h index e8579412ad214..d7ee4c6bad482 100644 --- a/include/linux/compiler-gcc.h +++ b/include/linux/compiler-gcc.h @@ -170,3 +170,5 @@ #else #define __diag_GCC_8(s) #endif + +#define __no_fgcse __attribute__((optimize("-fno-gcse"))) diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h index 19e58b9138a04..0454d82f8bd82 100644 --- a/include/linux/compiler_types.h +++ b/include/linux/compiler_types.h @@ -187,6 +187,10 @@ struct ftrace_likely_data { #define asm_volatile_goto(x...) asm goto(x) #endif +#ifndef __no_fgcse +# define __no_fgcse +#endif + /* Are two types/vars the same type (ignoring qualifiers)? */ #define __same_type(a, b) __builtin_types_compatible_p(typeof(a), typeof(b)) diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c index f2148db91439e..ceee0730fba58 100644 --- a/kernel/bpf/core.c +++ b/kernel/bpf/core.c @@ -1295,7 +1295,7 @@ bool bpf_opcode_in_insntable(u8 code) * * Decode and execute eBPF instructions. */ -static u64 ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack) +static u64 __no_fgcse ___bpf_prog_run(u64 *regs, const struct bpf_insn *insn, u64 *stack) { #define BPF_INSN_2_LBL(x, y) [BPF_##x | BPF_##y] = &&x##_##y #define BPF_INSN_3_LBL(x, y, z) [BPF_##x | BPF_##y | BPF_##z] = &&x##_##y##_##z -- 2.20.1