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=-0.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no 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 24D2FC2D0B1 for ; Fri, 6 Dec 2019 07:21:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id EF79621835 for ; Fri, 6 Dec 2019 07:20:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=dlink.ru header.i=@dlink.ru header.b="p5R61v4R" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726400AbfLFHU6 (ORCPT ); Fri, 6 Dec 2019 02:20:58 -0500 Received: from mail.dlink.ru ([178.170.168.18]:39462 "EHLO fd.dlink.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725858AbfLFHU6 (ORCPT ); Fri, 6 Dec 2019 02:20:58 -0500 Received: by fd.dlink.ru (Postfix, from userid 5000) id 6F7E41B21545; Fri, 6 Dec 2019 10:20:53 +0300 (MSK) DKIM-Filter: OpenDKIM Filter v2.11.0 fd.dlink.ru 6F7E41B21545 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=dlink.ru; s=mail; t=1575616853; bh=YBcb2XIhpGvQl1++v0zJOJ1RxMw2N0RI5FMDXHCH0qA=; h=Date:From:To:Cc:Subject:In-Reply-To:References; b=p5R61v4RR88Ijn3tXZdHEevK2Wg/cSQTyAZgPSNpcQ9ZAvQmfxseTgq5xYQXBhl40 TWLwSh4S8Y88vlPq2CK2Qi++JDSCaWwH6hp1WBL7rC6JP3CZ5KuyLLouRt/QBD2meU GNSDYdNkkDLsOHOAAP7MeEF/Rp2uODW7Q4XXdYK0= Received: from mail.rzn.dlink.ru (mail.rzn.dlink.ru [178.170.168.13]) by fd.dlink.ru (Postfix) with ESMTP id 54F6E1B21308; Fri, 6 Dec 2019 10:20:41 +0300 (MSK) DKIM-Filter: OpenDKIM Filter v2.11.0 fd.dlink.ru 54F6E1B21308 Received: from mail.rzn.dlink.ru (localhost [127.0.0.1]) by mail.rzn.dlink.ru (Postfix) with ESMTP id 0DBDB1B226AC; Fri, 6 Dec 2019 10:20:41 +0300 (MSK) Received: from mail.rzn.dlink.ru (localhost [127.0.0.1]) by mail.rzn.dlink.ru (Postfix) with ESMTPA; Fri, 6 Dec 2019 10:20:41 +0300 (MSK) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Fri, 06 Dec 2019 10:20:40 +0300 From: Alexander Lobakin To: Paul Burton Cc: Paul Burton , Hassan Naveed , Ralf Baechle , James Hogan , Alexei Starovoitov , Daniel Borkmann , Martin KaFai Lau , Song Liu , Yonghong Song , Andrii Nakryiko , netdev@vger.kernel.org, bpf@vger.kernel.org, linux-mips@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: MIPS eBPF JIT support on pre-32R2 In-Reply-To: <20191205184450.lbrkenmursz4zpdm@lantea.localdomain> References: <09d713a59665d745e21d021deeaebe0a@dlink.ru> <20191205184450.lbrkenmursz4zpdm@lantea.localdomain> User-Agent: Roundcube Webmail/1.4.0 Message-ID: <647fa62c7111a27a2cc217cf06cbe355@dlink.ru> X-Sender: alobakin@dlink.ru Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Paul Burton wrote 05.12.2019 21:44: > Hi Alexander, Hi Paul! > On Thu, Dec 05, 2019 at 03:45:27PM +0300, Alexander Lobakin wrote: >> Hey all, >> >> I'm writing about lines arch/mips/net/ebpf_jit.c:1806-1807: >> >> if (!prog->jit_requested || MIPS_ISA_REV < 2) >> return prog; >> >> Do pre-32R2 architectures (32R1, maybe even R3000-like) actually >> support >> this eBPF JIT code? > > No, they don't; the eBPF JIT makes unconditional use of at least the > (d)ins & (d)ext instructions which were added in MIPSr2, so it would > result in reserved instruction exceptions & panics if enabled on > pre-MIPSr2 CPUs. > >> If they do, then the condition 'MIPS_ISA_REV < 2' >> should be removed as it is always true for them and tells CC to remove >> JIT completely. >> >> If they don't support instructions from this JIT, then the line >> arch/mips/Kconfig:50: >> >> select HAVE_EBPF_JIT if (!CPU_MICROMIPS) >> >> should be changed to something like: >> >> select HAVE_EBPF_JIT if !CPU_MICROMIPS && TARGET_ISA_REV >= 2 >> >> (and then the mentioned 'if' condition would become redundant) > > Good spot; I agree entirely, this dependency should be reflected in > Kconfig. > >> At the moment it is possible to build a kernel without both JIT and >> interpreter, but with CONFIG_BPF_SYSCALL=y (what should not be allowed >> I suppose?) within the following configuration: >> >> - select any pre-32R2 CPU (e.g. CONFIG_CPU_MIPS32_R1); >> - enable CONFIG_BPF_JIT (CONFIG_MIPS_EBPF_JIT will be autoselected); >> - enable CONFIG_BPF_JIT_ALWAYS_ON (this removes BPF interpreter from >> the system). >> >> I may prepare a proper patch by myself if needed (after >> clarification). > > That would be great, thanks! Great, I'll send it in about ~2-3 hours. > One thing to note is that I hope we'll restore the cBPF JIT with this > patch: > > https://lore.kernel.org/linux-mips/20191205182318.2761605-1-paulburton@kernel.org/T/#u > > The cBPF JIT looks like it should work on older pre-MIPSr2 CPUs, so the > only way this is relevant is that your patch might have a minor > conflict. But I thought I'd mention it anyway :) Yes, I thought about this too. If pre-32R2 CPUs don't support our eBPF JIT, we'd better restore cBPF for them, so they could speed-up at least "classic" instructions. Glad you've decided to do that. > Thanks, > Paul Regards, ᚷ ᛖ ᚢ ᚦ ᚠ ᚱ