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=-5.7 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 EB8E8C433E0 for ; Sun, 17 Jan 2021 17:28:03 +0000 (UTC) Received: from merlin.infradead.org (merlin.infradead.org [205.233.59.134]) (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 A89772222F for ; Sun, 17 Jan 2021 17:28:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A89772222F Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.microsoft.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+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=merlin.20170209; h=Sender:Content-Transfer-Encoding: Content-Type:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=nlTeer8PPL//MK5xddbEeoWQs3LvRAnWsOSOO/PrU9A=; b=Umuu2G4rf40VtrAa3LeOdAMBE O1y/9d0UXg5hOFOpxcClgjqlJkCApaPaUnRfmACxETg8nks3LBGZ2jx/LZqEZJBTWEnengp6bOwwB wwKk8pzq8Aanho2d7/TMYtWOr2zrcnak4BbQXBXctrCD/9/c00aEz+es22O+WB0NnUafKIKLO4WmG P/u+G69CTeB/qz4nVaxQPY8sYlheMeLYd6ppQcZ9YoCY6omHdrCdVBqSbS2kH3SaEMQP1Va/mG90Z XwfIK6r/u/5CrnbMR89+S03RbuKnGoyDJC58tMKRC5LdKkHoeCtIvw40q8FJV3wHp8GCFzHcpPtSG wO5UrSRsA==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l1BoE-00024D-VN; Sun, 17 Jan 2021 17:25:51 +0000 Received: from linux.microsoft.com ([13.77.154.182]) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1l1BoA-00023d-3m for linux-arm-kernel@lists.infradead.org; Sun, 17 Jan 2021 17:25:48 +0000 Received: from [192.168.254.32] (unknown [47.187.219.45]) by linux.microsoft.com (Postfix) with ESMTPSA id A8F0120B7192; Sun, 17 Jan 2021 09:25:42 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com A8F0120B7192 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1610904343; bh=dSxgyZILd6ePeQFGFSfItK/jBXk7vqxGoh5JR1/STnU=; h=Subject:To:Cc:References:From:Date:In-Reply-To:From; b=NaeBDi7O+56Gh0KonoBTBOjzfe3hfWYRl6mCpb1uojoZiibtZgwkuczXfumqIW1Xm qLblMkxvZUO1VO/QuGbp2KyGbuFyRon9vp3BruaNST8Hd5OpKIg1DLmuMYc+LN2Pre JQ1/PqvGORj1UhGIMXUax1j8+WP3nJY/6SRq7ObU= Subject: Re: Live patching on ARM64 To: Mark Rutland References: <20210115123347.GB39776@C02TD0UTHF1T.local> From: "Madhavan T. Venkataraman" Message-ID: Date: Sun, 17 Jan 2021 11:25:41 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20210115123347.GB39776@C02TD0UTHF1T.local> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210117_122546_482243_ABC8280A X-CRM114-Status: GOOD ( 29.35 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Julien Thierry , linux-kernel@vger.kernel.org, Mark Brown , jpoimboe@redhat.com, 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+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 1/15/21 6:33 AM, Mark Rutland wrote: >> It looks like the most recent work in this area has been from the >> following folks: >> >> Mark Brown and Mark Rutland: >> Kernel changes to providing reliable stack traces. >> >> Julien Thierry: >> Providing ARM64 support in objtool. >> >> Torsten Duwe: >> Ftrace with regs. > > IIRC that's about right. I'm also trying to make arm64 patch-safe (more > on that below), and there's a long tail of work there for anyone > interested. > OK. >> I apologize if I have missed anyone else who is working on Live Patching >> for ARM64. Do let me know. >> >> Is there any work I can help with? Any areas that need investigation, any code >> that needs to be written, any work that needs to be reviewed, any testing that >> needs to done? You folks are probably super busy and would not mind an extra >> hand. > > One general thing that I believe we'll need to do is to rework code to > be patch-safe (which implies being noinstr-safe too). For example, we'll > need to rework the instruction patching code such that this cannot end > up patching itself (or anything that has instrumented it) in an unsafe > way. > OK. > Once we have objtool it should be possible to identify those cases > automatically. Currently I'm aware that we'll need to do something in at > least the following places: > > * The entry code -- I'm currently chipping away at this. > OK. > * The insn framework (which is used by some patching code), since the > bulk of it lives in arch/arm64/kernel/insn.c and isn't marked noinstr. > > We can probably shift the bulk of the aarch64_insn_gen_*() and > aarch64_get_*() helpers into a header as __always_inline functions, > which would allow them to be used in noinstr code. As those are > typically invoked with a number of constant arguments that the > compiler can fold, this /might/ work out as an optimization if the > compiler can elide the error paths. > > * The alternatives code, since we call instrumentable and patchable > functions between updating instructions and performing all the > necessary maintenance. There are a number of cases within > __apply_alternatives(), e.g. > > - test_bit() > - cpus_have_cap() > - pr_info_once() > - lm_alias() > - alt_cb, if the callback is not marked as noinstr, or if it calls > instrumentable code (e.g. from the insn framework). > - clean_dcache_range_nopatch(), as read_sanitised_ftr_reg() and > related code can be instrumented. > > This might need some underlying rework elsewhere (e.g. in the > cpufeature code, or atomics framework). > OK. > So on the kernel side, maybe a first step would be to try to headerize > the insn generation code as __always_inline, and see whether that looks > ok? With that out of the way it'd be a bit easier to rework patching > code depending on the insn framework. > OK. I have an understanding of some of the above already. I will come up to speed on the others. I will email you any questions I might have. > I'm not sure about the objtool side, so I'll leave that to Julien and co > to answer. > Thanks for the information. Madhavan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel