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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 1C475C433DF for ; Wed, 3 Jun 2020 12:21:52 +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 E020020674 for ; Wed, 3 Jun 2020 12:21:51 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="KvSLVOyT" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E020020674 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com 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-Type: Content-Transfer-Encoding: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=f4hsZ18q6A20xTBkc9AkfhyiWMPAudRCgnBd+CwWScQ=; b=KvSLVOyTLvdg/MGTw5F3+3gis AY7rZK/C5STJavX3Kks99+KeYB3nTok+Abm7fxUV4qSzwPN1EIzPWw96faigKG7J03Hhzg2d+QOyk 99wztSzhHbYDHHs9gX5QIYQpWl03RPV0uE21qA5ADfdBy9EMvJfh2szuX6Ir3cq8py4GaUZaTe5ya IjnxT9WGUNAjy6ueu4V+S86wuV29It7E6awA/Ss1pQHriCsxdR3Udx5FZ6YuOdJt40v7eetDe1pWR ESSmUCf7onNfzpMrorDKXWbidbmeEqZ84QhSEeNXNvSY7J6O1sEJreRAINyNsSLPJNDuq8dRDG3g7 A66ZUec7w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jgSOu-0006sn-LH; Wed, 03 Jun 2020 12:21:44 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jgSOr-0006s0-CR for linux-arm-kernel@lists.infradead.org; Wed, 03 Jun 2020 12:21:43 +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 DCEE531B; Wed, 3 Jun 2020 05:21:37 -0700 (PDT) Received: from [10.57.0.45] (unknown [10.57.0.45]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A2F1A3F305; Wed, 3 Jun 2020 05:21:34 -0700 (PDT) Subject: Re: [PATCH 2/2] coresight: tmc: Add shutdown callback for TMC ETR/ETF To: Sai Prakash Ranjan References: <28123d1e19f235f97555ee36a5ed8b52d20cbdea.1590947174.git.saiprakash.ranjan@codeaurora.org> <20200601212858.GB24287@xps15> <1549935cf69ac3a006f32eb278821027@codeaurora.org> From: Robin Murphy Message-ID: <6c1a4fbd-98cb-a49c-0ced-1318d5d5e7c8@arm.com> Date: Wed, 3 Jun 2020 13:21:30 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:68.0) Gecko/20100101 Thunderbird/68.8.0 MIME-Version: 1.0 In-Reply-To: <1549935cf69ac3a006f32eb278821027@codeaurora.org> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200603_052141_469463_1CD9C63E X-CRM114-Status: GOOD ( 18.13 ) 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: Mathieu Poirier , Suzuki K Poulose , linux-arm-msm@vger.kernel.org, coresight@lists.linaro.org, linux-kernel@vger.kernel.org, Stephen Boyd , linux-arm-kernel@lists.infradead.org, Mike Leach Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-06-03 13:00, Sai Prakash Ranjan wrote: > Hi Robin, Mathieu > > On 2020-06-03 17:07, Robin Murphy wrote: >> On 2020-06-01 22:28, Mathieu Poirier wrote: >>> That being said I'm sure that dependencies on an IOMMU isn't a >>> problem confined >>> to coresight. I am adding Robin Murphy, who added this commit [1], to >>> the thread >>> in the hope that he can provide guidance on the right way to do this. >> >> Right, it's not specific to CoreSight, and it's not even specific to >> IOMMUs really. In short, blame kexec ;) >> > > Yes it is not specific to coresight, we are targeting this for all > consumers/clients of SMMU(atleast on SC7180 SoC). We have display throwing > NoC/interconnect errors[1] during reboot after SMMU is disabled. > This is also not specific to kexec either as you explained here [2] about > a case with display which is exacly what is happening in our system [1]. Sure, but those instances are begging the question of why the SMMU is disabled at reboot in the first place ;) Robin. > > [1] > https://lore.kernel.org/lkml/1591009402-681-1-git-send-email-mkrishn@codeaurora.org/ > > [2] > https://lore.kernel.org/lkml/5858bdac-b7f9-ac26-0c0d-c9653cef841d@arm.com/ > >> The fundamental thing is that devices should stop any DMA activity at >> shutdown. For a normal poweroff you can typically get away without >> doing so, but over kexec, ongoing DMA traffic may corrupt memory in >> the new kernel (at worst, I think even DMA reads could potentially >> cause unexpected cache behaviour that might lead to mishaps, given the >> right combination of memory attributes). >> >> IOMMUs merely help to make the situation more serious. For similar >> kexec reasons, they need to disable any existing translations at >> shutdown (imagine if the second kernel didn't have an IOMMU driver). >> And at that point, even the normal poweroff case becomes problematic, >> because any device DMA that hasn't been shut down beforehand is now >> not necessarily going benignly to memory as it would in the no-IOMMU >> case above, but potentially to random physical addresses, with all the >> hilarity ensuing that you would expect from that. >> > > Thanks, > Sai _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel