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=-3.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS 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 9FCA5C43387 for ; Fri, 4 Jan 2019 18:06:59 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 65D05218D3 for ; Fri, 4 Jan 2019 18:06:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="uaGykmv3" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 65D05218D3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=goodmis.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Subject: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=O9Ln5qDEhDgVQ67e0OooLg6xcyExmyqmhQZY6nu+oOY=; b=uaGykmv3IYSbUL /U7CtwiQqGJDHdIr8ZMwUEtOmZwR05hGlIws7zQe/mw9f5FmTNYHqS28YnBco1CSMlLRrXIliO6BQ 5AM4UKprLCPf4ZvsPyDjDIkb4xAI8xTYkh9mEtfP8HdSzaJSnY0yKS9fT/+iOjnEpLv8/9Ztz7Bsm H0OEWdVoCjym0Um++83KiG0fJopN7nkVszzJDK1zPFdoTg3D+rwQblCAnsyXBTaxS4x+9cuUzAvaG Q7b9Ng70cuW+cLy7vtvFEZYnuLng8LKFPrJK03MxFv4vC6gKqUyXP/WQiwQn1bz9NKedMN1hsd3+W lZ/7kO2itXmiYaVsiZbw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gfTs0-0002nf-GV; Fri, 04 Jan 2019 18:06:56 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gfTrw-0002kB-RG for linux-arm-kernel@lists.infradead.org; Fri, 04 Jan 2019 18:06:54 +0000 Received: from gandalf.local.home (cpe-66-24-56-78.stny.res.rr.com [66.24.56.78]) (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 4D612218D3; Fri, 4 Jan 2019 18:06:50 +0000 (UTC) Date: Fri, 4 Jan 2019 13:06:48 -0500 From: Steven Rostedt To: Mark Rutland Subject: Re: [PATCH v6] arm64: implement ftrace with regs Message-ID: <20190104130648.02657f3f@gandalf.local.home> In-Reply-To: <20190104175017.GA7157@lakrids.cambridge.arm.com> References: <20190104141053.360F768D93@newverein.lst.de> <20190104175017.GA7157@lakrids.cambridge.arm.com> X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190104_100652_900334_96DB267E X-CRM114-Status: GOOD ( 13.21 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Arnd Bergmann , Julien Thierry , Catalin Marinas , Ard Biesheuvel , Will Deacon , linux-kernel@vger.kernel.org, AKASHI Takahiro , Ingo Molnar , Torsten Duwe , Josh Poimboeuf , Amit Daniel Kachhap , live-patching@vger.kernel.org, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, 4 Jan 2019 17:50:18 +0000 Mark Rutland wrote: > At Linux Plumbers, I had a conversation with Steve Rostedt, and we came > to the conclusion that (withut heavyweight synchronization) patching two > NOPs at runtime isn't safe, since a CPU might have executed the first > NOP as a NOP before another CPU patches both instructions. So a CPU > might execute: > > NOP > BL ftrace_regs_caller > > ... rather than the expected: > > MOV X9, X30 > BL ftrace_regs_caller > > ... and therefore X9 contains some UNKNOWN value, rather than the > original LR value. > > I wonder if we could solve that by patching the kernel at build-time, to > add the MOV X9, X30 in place of the first NOP. If we were to do that, we > could also update the addresses to pooint at the second NOP, simplifying > the changes to the runtime code. You can also patch it at boot up when there's only one CPU running, and interrupts are disabled. -- Steve _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel