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=-13.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_IN_DEF_DKIM_WL 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 66707C49EA4 for ; Tue, 22 Jun 2021 20:07:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4B44561352 for ; Tue, 22 Jun 2021 20:07:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233213AbhFVUJe (ORCPT ); Tue, 22 Jun 2021 16:09:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38348 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233094AbhFVUJU (ORCPT ); Tue, 22 Jun 2021 16:09:20 -0400 Received: from mail-qk1-x735.google.com (mail-qk1-x735.google.com [IPv6:2607:f8b0:4864:20::735]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 54EE1C0611FA for ; Tue, 22 Jun 2021 13:06:32 -0700 (PDT) Received: by mail-qk1-x735.google.com with SMTP id f70so42683292qke.13 for ; Tue, 22 Jun 2021 13:06:32 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=vFcGA/y37DyPbCA16zXcaXhlM22oPoQGg4ooUNJCkAo=; b=oE70xO3DZnhRS9D0CKfrI5YQLEhrR7v66Yym0RkSj6xNG+HAKLJcuW5poY76Ikj1m3 izn/UO02g39+emV4Srav7XrCyr7lyK38LGwCo4bFfY7GFuLXhAumopaixv/gyHh0QE92 WJdPx8N8/fXlatfvX+CjN5W5ZdTPjS8OsP/hQdiyMgsfRByf5F7GYMu4wok+ZLpWy7Go VwPB2Gl8gaJN2+Eiy5dEVP+RngrjMEVoQ345F20TCtAUY1HXDlkCesirVpkNcH1nQhU9 xIoBnzRQueZgHpVHm0loRAMptrTdXBfsEm2q8KuRcKkEAeAkA1zvrNa10Uqbd3GsgRhS kiQg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=vFcGA/y37DyPbCA16zXcaXhlM22oPoQGg4ooUNJCkAo=; b=S+GzplWd6QZGZZNqvxIwdi1G0sisURNs7H3zPw0EphDkwBtfTqNl7t2nqr4AwrARsh nIvv/Bz2dWOzTwMfDd8NXwpyvUOFo+RImzXoIuVFwX8zBy1Gi6VNM7H3EEKAvUcIj9js ret4ejozdpPYjNZZOym8SsrQgZKGKTq0a1OV5/EMkIs48TywNI92l7Fx3/UWYQV4kSzY rZBwqqRULoBlSKE9/0sfteYLNIKRuZah5H41zzpx9sbdz+Z1mG1RHlFz09aUssXZFM4Y kRQXwx+86MobeRSkWgzxZgJ91ue1eixI4lEOW4EYy1AC8CTFWy6B5QkLCxwTIDRJBs4f Sh7w== X-Gm-Message-State: AOAM532o6ZIct8dgB07jlk6CbWjaP7YpUekDSO+W62/4DEJOzJfIj79U Lj9+z4sPuGJK8VWgHZnGh8E9PiTpeuWoJz12DDjAUQ== X-Google-Smtp-Source: ABdhPJwancDB4ysHtZ3UshEMyFDmCd7rFxYJq2frEz/W+UiMsBDDnOPFY6v+z4No4rWO4LesJMIAed8JJfH7yL+cobo= X-Received: by 2002:a25:4c42:: with SMTP id z63mr7100722yba.20.1624392391257; Tue, 22 Jun 2021 13:06:31 -0700 (PDT) MIME-Version: 1.0 References: <20210621235248.2521620-1-dianders@chromium.org> <067dd86d-da7f-ac83-6ce6-b8fd5aba0b6f@arm.com> <20210622200219.GA28722@robh.at.kernel.org> In-Reply-To: <20210622200219.GA28722@robh.at.kernel.org> From: Saravana Kannan Date: Tue, 22 Jun 2021 13:05:55 -0700 Message-ID: Subject: Re: [PATCH 0/6] iommu: Enable devices to request non-strict DMA, starting with QCom SD/MMC To: Rob Herring Cc: Doug Anderson , Robin Murphy , Greg Kroah-Hartman , "Rafael J. Wysocki" , "Rafael J. Wysocki" , Will Deacon , Joerg Roedel , Bjorn Andersson , Ulf Hansson , Adrian Hunter , Bjorn Helgaas , Rob Clark , linux-arm-msm , linux-pci@vger.kernel.org, quic_c_gdjako@quicinc.com, "list@263.net:IOMMU DRIVERS , Joerg Roedel ," , Sonny Rao , Sai Prakash Ranjan , Linux MMC List , Veerabhadrarao Badiganti , Rajat Jain , Joel Fernandes , Andy Gross , Bartosz Golaszewski , Dan Williams , Geert Uytterhoeven , Heikki Krogerus , Randy Dunlap , LKML Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-arm-msm@vger.kernel.org On Tue, Jun 22, 2021 at 1:02 PM Rob Herring wrote: > > On Tue, Jun 22, 2021 at 09:06:02AM -0700, Doug Anderson wrote: > > Hi, > > > > On Tue, Jun 22, 2021 at 4:35 AM Robin Murphy wrote: > > > > > > Hi Doug, > > > > > > On 2021-06-22 00:52, Douglas Anderson wrote: > > > > > > > > This patch attempts to put forward a proposal for enabling non-strict > > > > DMA on a device-by-device basis. The patch series requests non-strict > > > > DMA for the Qualcomm SDHCI controller as a first device to enable, > > > > getting a nice bump in performance with what's believed to be a very > > > > small drop in security / safety (see the patch for the full argument). > > > > > > > > As part of this patch series I am end up slightly cleaning up some of > > > > the interactions between the PCI subsystem and the IOMMU subsystem but > > > > I don't go all the way to fully remove all the tentacles. Specifically > > > > this patch series only concerns itself with a single aspect: strict > > > > vs. non-strict mode for the IOMMU. I'm hoping that this will be easier > > > > to talk about / reason about for more subsystems compared to overall > > > > deciding what it means for a device to be "external" or "untrusted". > > > > > > > > If something like this patch series ends up being landable, it will > > > > undoubtedly need coordination between many maintainers to land. I > > > > believe it's fully bisectable but later patches in the series > > > > definitely depend on earlier ones. Sorry for the long CC list. :( > > > > > > Unfortunately, this doesn't work. In normal operation, the default > > > domains should be established long before individual drivers are even > > > loaded (if they are modules), let alone anywhere near probing. The fact > > > that iommu_probe_device() sometimes gets called far too late off the > > > back of driver probe is an unfortunate artefact of the original > > > probe-deferral scheme, and causes other problems like potentially > > > malformed groups - I've been forming a plan to fix that for a while now, > > > so I for one really can't condone anything trying to rely on it. > > > Non-deterministic behaviour based on driver probe order for multi-device > > > groups is part of the existing problem, and your proposal seems equally > > > vulnerable to that too. > > > > Doh! :( I definitely can't say I understand the iommu subsystem > > amazingly well. It was working for me, but I could believe that I was > > somehow violating a rule somewhere. > > > > I'm having a bit of a hard time understanding where the problem is > > though. Is there any chance that you missed the part of my series > > where I introduced a "pre_probe" step? Specifically, I see this: > > > > * really_probe() is called w/ a driver and a device. > > * -> calls dev->bus->dma_configure() w/ a "struct device *" > > * -> eventually calls iommu_probe_device() w/ the device. > > * -> calls iommu_alloc_default_domain() w/ the device > > * -> calls iommu_group_alloc_default_domain() > > * -> always allocates a new domain > > > > ...so we always have a "struct device" when a domain is allocated if > > that domain is going to be associated with a device. > > > > I will agree that iommu_probe_device() is called before the driver > > probe, but unless I missed something it's after the device driver is > > loaded. ...and assuming something like patch #1 in this series looks > > OK then iommu_probe_device() will be called after "pre_probe". > > > > So assuming I'm not missing something, I'm not actually relying the > > IOMMU getting init off the back of driver probe. > > > > > > > FWIW we already have a go-faster knob for people who want to tweak the > > > security/performance compromise for specific devices, namely the sysfs > > > interface for changing a group's domain type before binding the relevant > > > driver(s). Is that something you could use in your application, say from > > > an initramfs script? > > > > We've never had an initramfs script in Chrome OS. I don't know all the > > history of why (I'm trying to check), but I'm nearly certain it was a > > conscious decision. Probably it has to do with the fact that we're not > > trying to build a generic distribution where a single boot source can > > boot a huge variety of hardware. We generally have one kernel for a > > class of devices. I believe avoiding the initramfs just keeps things > > simpler. > > > > I think trying to revamp Chrome OS to switch to an initramfs type > > system would be a pretty big undertaking since (as I understand it) > > you can't just run a little command and then return to the normal boot > > flow. Once you switch to initramfs you're committing to finding / > > setting up the rootfs yourself and on Chrome OS I believe that means a > > whole bunch of dm-verity work. > > > > > > ...so probably the initramfs is a no-go for me, but I'm still crossing > > my fingers that the pre_probe() might be legit if you take a second > > look at it? > > Couldn't you have a driver flag that has the same effect as twiddling > sysfs? At the being of probe, check the flag and go set the underlying > sysfs setting in the device. My understanding of what Robin is saying is that we'd need this info well before the driver is even available. The pre_probe() is effectively doing the same thing you are suggesting. > Though you may want this to be per device, not per driver. To do that > early, I think you'd need a DT property. I wouldn't be totally opposed > to that and I appreciate you not starting there. :) Which is what I'm suggest elsewhere in the thread: https://lore.kernel.org/lkml/CAGETcx83qCZF5JN5cqXxdSFiEgfc4jYESJg-RepL2wJXJv0Eww@mail.gmail.com/ -Saravana 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=-3.5 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 4EFA5C49EA4 for ; Tue, 22 Jun 2021 20:06:37 +0000 (UTC) Received: from smtp3.osuosl.org (smtp3.osuosl.org [140.211.166.136]) (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 E5C6761352 for ; 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Tue, 22 Jun 2021 13:06:31 -0700 (PDT) MIME-Version: 1.0 References: <20210621235248.2521620-1-dianders@chromium.org> <067dd86d-da7f-ac83-6ce6-b8fd5aba0b6f@arm.com> <20210622200219.GA28722@robh.at.kernel.org> In-Reply-To: <20210622200219.GA28722@robh.at.kernel.org> Date: Tue, 22 Jun 2021 13:05:55 -0700 Message-ID: Subject: Re: [PATCH 0/6] iommu: Enable devices to request non-strict DMA, starting with QCom SD/MMC To: Rob Herring Cc: Ulf Hansson , Heikki Krogerus , "Rafael J. Wysocki" , linux-pci@vger.kernel.org, Joel Fernandes , Rajat Jain , Will Deacon , Rob Clark , "Rafael J. Wysocki" , quic_c_gdjako@quicinc.com, Bartosz Golaszewski , Andy Gross , Geert Uytterhoeven , Veerabhadrarao Badiganti , linux-arm-msm , Bjorn Helgaas , Dan Williams , Adrian Hunter , Sonny Rao , Greg Kroah-Hartman , Randy Dunlap , Linux MMC List , Doug Anderson , LKML , "list@263.net:IOMMU DRIVERS , Joerg Roedel , " , Robin Murphy X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Saravana Kannan via iommu Reply-To: Saravana Kannan Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Tue, Jun 22, 2021 at 1:02 PM Rob Herring wrote: > > On Tue, Jun 22, 2021 at 09:06:02AM -0700, Doug Anderson wrote: > > Hi, > > > > On Tue, Jun 22, 2021 at 4:35 AM Robin Murphy wrote: > > > > > > Hi Doug, > > > > > > On 2021-06-22 00:52, Douglas Anderson wrote: > > > > > > > > This patch attempts to put forward a proposal for enabling non-strict > > > > DMA on a device-by-device basis. The patch series requests non-strict > > > > DMA for the Qualcomm SDHCI controller as a first device to enable, > > > > getting a nice bump in performance with what's believed to be a very > > > > small drop in security / safety (see the patch for the full argument). > > > > > > > > As part of this patch series I am end up slightly cleaning up some of > > > > the interactions between the PCI subsystem and the IOMMU subsystem but > > > > I don't go all the way to fully remove all the tentacles. Specifically > > > > this patch series only concerns itself with a single aspect: strict > > > > vs. non-strict mode for the IOMMU. I'm hoping that this will be easier > > > > to talk about / reason about for more subsystems compared to overall > > > > deciding what it means for a device to be "external" or "untrusted". > > > > > > > > If something like this patch series ends up being landable, it will > > > > undoubtedly need coordination between many maintainers to land. I > > > > believe it's fully bisectable but later patches in the series > > > > definitely depend on earlier ones. Sorry for the long CC list. :( > > > > > > Unfortunately, this doesn't work. In normal operation, the default > > > domains should be established long before individual drivers are even > > > loaded (if they are modules), let alone anywhere near probing. The fact > > > that iommu_probe_device() sometimes gets called far too late off the > > > back of driver probe is an unfortunate artefact of the original > > > probe-deferral scheme, and causes other problems like potentially > > > malformed groups - I've been forming a plan to fix that for a while now, > > > so I for one really can't condone anything trying to rely on it. > > > Non-deterministic behaviour based on driver probe order for multi-device > > > groups is part of the existing problem, and your proposal seems equally > > > vulnerable to that too. > > > > Doh! :( I definitely can't say I understand the iommu subsystem > > amazingly well. It was working for me, but I could believe that I was > > somehow violating a rule somewhere. > > > > I'm having a bit of a hard time understanding where the problem is > > though. Is there any chance that you missed the part of my series > > where I introduced a "pre_probe" step? Specifically, I see this: > > > > * really_probe() is called w/ a driver and a device. > > * -> calls dev->bus->dma_configure() w/ a "struct device *" > > * -> eventually calls iommu_probe_device() w/ the device. > > * -> calls iommu_alloc_default_domain() w/ the device > > * -> calls iommu_group_alloc_default_domain() > > * -> always allocates a new domain > > > > ...so we always have a "struct device" when a domain is allocated if > > that domain is going to be associated with a device. > > > > I will agree that iommu_probe_device() is called before the driver > > probe, but unless I missed something it's after the device driver is > > loaded. ...and assuming something like patch #1 in this series looks > > OK then iommu_probe_device() will be called after "pre_probe". > > > > So assuming I'm not missing something, I'm not actually relying the > > IOMMU getting init off the back of driver probe. > > > > > > > FWIW we already have a go-faster knob for people who want to tweak the > > > security/performance compromise for specific devices, namely the sysfs > > > interface for changing a group's domain type before binding the relevant > > > driver(s). Is that something you could use in your application, say from > > > an initramfs script? > > > > We've never had an initramfs script in Chrome OS. I don't know all the > > history of why (I'm trying to check), but I'm nearly certain it was a > > conscious decision. Probably it has to do with the fact that we're not > > trying to build a generic distribution where a single boot source can > > boot a huge variety of hardware. We generally have one kernel for a > > class of devices. I believe avoiding the initramfs just keeps things > > simpler. > > > > I think trying to revamp Chrome OS to switch to an initramfs type > > system would be a pretty big undertaking since (as I understand it) > > you can't just run a little command and then return to the normal boot > > flow. Once you switch to initramfs you're committing to finding / > > setting up the rootfs yourself and on Chrome OS I believe that means a > > whole bunch of dm-verity work. > > > > > > ...so probably the initramfs is a no-go for me, but I'm still crossing > > my fingers that the pre_probe() might be legit if you take a second > > look at it? > > Couldn't you have a driver flag that has the same effect as twiddling > sysfs? At the being of probe, check the flag and go set the underlying > sysfs setting in the device. My understanding of what Robin is saying is that we'd need this info well before the driver is even available. The pre_probe() is effectively doing the same thing you are suggesting. > Though you may want this to be per device, not per driver. To do that > early, I think you'd need a DT property. I wouldn't be totally opposed > to that and I appreciate you not starting there. :) Which is what I'm suggest elsewhere in the thread: https://lore.kernel.org/lkml/CAGETcx83qCZF5JN5cqXxdSFiEgfc4jYESJg-RepL2wJXJv0Eww@mail.gmail.com/ -Saravana _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu