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 Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 8EF76C32771 for ; Mon, 26 Sep 2022 17:45:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Ym6RPov/lhf0NExNskj5eZDBZYUZmv6/mCe2Ukxkkhw=; b=y7bTATi0hOscwW tW/cqAfnvAT2DEQqOmo/Q9Hn9Ro+MAzVKZ7uK7WVcH1mFlMOtCgsgLxztSvV88N6oeJVI+Egk0JNL +Pw8UHKDhjYa8B5FnfYHYjfQPKxWzmTm25kdyO5JmVwEhVqFsLVXB0LYodX/C1L7SoTZ+tV69WOtv yjIhfFgpBFuI8OyHKOxWBcQySBa5coUi4M2gD9i/gYKxDrW+IaNkE8v+UwyXwblsv8rbiC/y4y5wn socw6hCJ2lmAN1HYLYGWFaECNwxTuJz4bGsantu4EHaVl27A4JiZ8tkkPPDMuqjI1aoGFtpBYHWd7 YvPevh7louaNWehXlSRA==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ocs9M-0065VY-4A; Mon, 26 Sep 2022 17:44:12 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1ocs9H-0065UI-W2 for linux-arm-kernel@lists.infradead.org; Mon, 26 Sep 2022 17:44:10 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4F7921CE2; Mon, 26 Sep 2022 10:44:08 -0700 (PDT) Received: from FVFF77S0Q05N (unknown [10.57.81.104]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9DA163F73B; Mon, 26 Sep 2022 10:43:57 -0700 (PDT) Date: Mon, 26 Sep 2022 18:43:51 +0100 From: Mark Rutland To: Catalin Marinas Cc: Daniel Borkmann , Xu Kuohai , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, bpf@vger.kernel.org, Florent Revest , Will Deacon , Jean-Philippe Brucker , Steven Rostedt , Ingo Molnar , Oleg Nesterov , Alexei Starovoitov , Andrii Nakryiko , Martin KaFai Lau , Song Liu , Yonghong Song , John Fastabend , KP Singh , Stanislav Fomichev , Hao Luo , Jiri Olsa , Zi Shen Lim , Pasha Tatashin , Ard Biesheuvel , Marc Zyngier , Guo Ren , Masami Hiramatsu Subject: Re: [PATCH bpf-next v2 0/4] Add ftrace direct call for arm64 Message-ID: References: <20220913162732.163631-1-xukuohai@huaweicloud.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220926_104408_172038_80647383 X-CRM114-Status: GOOD ( 26.00 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Sep 26, 2022 at 03:40:20PM +0100, Catalin Marinas wrote: > On Thu, Sep 22, 2022 at 08:01:16PM +0200, Daniel Borkmann wrote: > > On 9/13/22 6:27 PM, Xu Kuohai wrote: > > > This series adds ftrace direct call for arm64, which is required to attach > > > bpf trampoline to fentry. > > > > > > Although there is no agreement on how to support ftrace direct call on arm64, > > > no patch has been posted except the one I posted in [1], so this series > > > continues the work of [1] with the addition of long jump support. Now ftrace > > > direct call works regardless of the distance between the callsite and custom > > > trampoline. > > > > > > [1] https://lore.kernel.org/bpf/20220518131638.3401509-2-xukuohai@huawei.com/ > > > > > > v2: > > > - Fix compile and runtime errors caused by ftrace_rec_arch_init > > > > > > v1: https://lore.kernel.org/bpf/20220913063146.74750-1-xukuohai@huaweicloud.com/ > > > > > > Xu Kuohai (4): > > > ftrace: Allow users to disable ftrace direct call > > > arm64: ftrace: Support long jump for ftrace direct call > > > arm64: ftrace: Add ftrace direct call support > > > ftrace: Fix dead loop caused by direct call in ftrace selftest > > > > Given there's just a tiny fraction touching BPF JIT and most are around core arm64, > > it probably makes sense that this series goes via Catalin/Will through arm64 tree > > instead of bpf-next if it looks good to them. Catalin/Will, thoughts (Ack + bpf-next > > could work too, but I'd presume this just results in merge conflicts)? > > I think it makes sense for the series to go via the arm64 tree but I'd > like Mark to have a look at the ftrace changes first. >From a quick scan, I still don't think this is quite right, and as it stands I believe this will break backtracing (as the instructions before the function entry point will not be symbolized correctly, getting in the way of RELIABLE_STACKTRACE). I think I was insufficiently clear with my earlier feedback there, as I have a mechanism in mind that wa a little simpler. I'll try to reply with some more detail tomorrow, but I don't think this is the right approach, and as mentioned previously (and e.g. at LPC) I'd strongly prefer to *not* implement direct calls, so that we can have more consistent entry/exit handling. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel