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=-0.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 EA992C433E0 for ; Wed, 3 Jun 2020 12:01:26 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C704920678 for ; Wed, 3 Jun 2020 12:01:26 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=mg.codeaurora.org header.i=@mg.codeaurora.org header.b="EzPXgEAb" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725920AbgFCMB0 (ORCPT ); Wed, 3 Jun 2020 08:01:26 -0400 Received: from m43-7.mailgun.net ([69.72.43.7]:39093 "EHLO m43-7.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725855AbgFCMBZ (ORCPT ); Wed, 3 Jun 2020 08:01:25 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1591185685; h=Message-ID: References: In-Reply-To: Subject: Cc: To: From: Date: Content-Transfer-Encoding: Content-Type: MIME-Version: Sender; bh=SeSF64gWAAvQHU3nZPOI+yYNnSV/P3R4z/7sHFFTb98=; b=EzPXgEAbFh38tykk1LdvnKmhdjDrM8aOA2OBo1TqMCNnUVnDjiaatGfpPnpF/SI1afS9b3hl hnov8cXdsBiyRXpKBbvky4QzUjSyUS0sVz1S9ojOmj637NqFmXql/XWZn+LliNYtgoFR9kZ9 iWj+rFFdWfpRpWQm2b4ymglzDko= X-Mailgun-Sending-Ip: 69.72.43.7 X-Mailgun-Sid: WyI1MzIzYiIsICJsaW51eC1hcm0tbXNtQHZnZXIua2VybmVsLm9yZyIsICJiZTllNGEiXQ== Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n10.prod.us-east-1.postgun.com with SMTP id 5ed790f9ea0dfa490e142252 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Wed, 03 Jun 2020 12:00:57 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 46D94C43391; Wed, 3 Jun 2020 12:00:56 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: saiprakash.ranjan) by smtp.codeaurora.org (Postfix) with ESMTPSA id 94B2FC433CA; Wed, 3 Jun 2020 12:00:55 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 03 Jun 2020 17:30:55 +0530 From: Sai Prakash Ranjan To: Robin Murphy Cc: Mathieu Poirier , Suzuki K Poulose , Mike Leach , linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, coresight@lists.linaro.org, Stephen Boyd Subject: Re: [PATCH 2/2] coresight: tmc: Add shutdown callback for TMC ETR/ETF In-Reply-To: References: <28123d1e19f235f97555ee36a5ed8b52d20cbdea.1590947174.git.saiprakash.ranjan@codeaurora.org> <20200601212858.GB24287@xps15> Message-ID: <1549935cf69ac3a006f32eb278821027@codeaurora.org> X-Sender: saiprakash.ranjan@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 Sender: linux-arm-msm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org 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]. [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 -- QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation