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=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_NEOMUTT autolearn=unavailable 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 580CFC31E4B for ; Fri, 14 Jun 2019 13:31:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 391A320851 for ; Fri, 14 Jun 2019 13:31:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727949AbfFNNbi (ORCPT ); Fri, 14 Jun 2019 09:31:38 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34012 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727673AbfFNNbi (ORCPT ); Fri, 14 Jun 2019 09:31:38 -0400 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id A2758308219E; Fri, 14 Jun 2019 13:31:37 +0000 (UTC) Received: from treble (ovpn-121-232.rdu2.redhat.com [10.10.121.232]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 620DC1798D; Fri, 14 Jun 2019 13:31:36 +0000 (UTC) Date: Fri, 14 Jun 2019 08:31:34 -0500 From: Josh Poimboeuf To: Peter Zijlstra Cc: Alexei Starovoitov , x86@kernel.org, linux-kernel@vger.kernel.org, Alexei Starovoitov , Daniel Borkmann , netdev@vger.kernel.org, bpf@vger.kernel.org, Song Liu , Kairui Song Subject: Re: [PATCH 7/9] x86/unwind/orc: Fall back to using frame pointers for generated code Message-ID: <20190614132615.qsbnvvnidba7cl55@treble> References: <4f536ec4facda97406273a22a4c2677f7cb22148.1560431531.git.jpoimboe@redhat.com> <20190613220054.tmonrgfdeie2kl74@ast-mbp.dhcp.thefacebook.com> <20190614013051.6gnwduy4dsygbamj@treble> <20190614014244.st7fbr6areazmyrb@ast-mbp.dhcp.thefacebook.com> <20190614015848.todgfogryjn573nd@treble> <20190614022848.ly4vlgsz6fa4bcbl@treble> <20190614045037.zinbi2sivthcfrtg@treble> <20190614060006.na6nfl6shawsyj3i@ast-mbp.dhcp.thefacebook.com> <20190614074136.GR3436@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20190614074136.GR3436@hirez.programming.kicks-ass.net> User-Agent: NeoMutt/20180716 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.47]); Fri, 14 Jun 2019 13:31:37 +0000 (UTC) Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Fri, Jun 14, 2019 at 09:41:37AM +0200, Peter Zijlstra wrote: > On Thu, Jun 13, 2019 at 11:00:09PM -0700, Alexei Starovoitov wrote: > > > There is something wrong with > > commit d15d356887e7 ("perf/x86: Make perf callchains work without CONFIG_FRAME_POINTER") > > It assumes we can always unwind stack, which is, imo, not a weird thing. > > > If I simply revert it and have CONFIG_UNWINDER_FRAME_POINTER=y > > JITed stacks work just fine, because > > bpf_get_stackid()->get_perf_callchain() > > need to start unwinding before any bpf stuff. > > How does stack unwinding work if we try and unwind from an interrupt > that hits inside a BPF program? That too needs to work properly. > > > After that commit it needs to go through which is a bug on its own. > > imo patch 1 doesn't really fix that issue. > > This we agree on, patch 1 doesn't solve that at all. But we also should > not loose the initial regs->ip value. > > > As far as mangled rbp can we partially undo old > > commit 177366bf7ceb ("bpf: change x86 JITed program stack layout") > > that introduced that rbp adjustment. > > > Going through bpf code is only interesting in case of panics somewhere > > in bpf helpers. Back then we didn't even have ksym of jited code. > > I disagree here, interrupts/NMIs hitting inside BPF should be able to > reliably unwind the entire stack. Back then is irrelevant, these days we > expect a reliable unwind. Right. Also, JIT code can call into C code, which could a) try to unwind b) call WARN() c) hit a panic d) get preempted by code which does any of the above e) etc > > Anyhow I agree that we need to make the jited frame proper, > > but unwinding need to start before any bpf stuff. > > That's a bigger issue. > > I strongly disagree, we should be able to unwind through bpf. -- Josh