From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lu Baolu Subject: Re: [PATCH v3 02/10] swiotlb: Factor out slot allocation and free Date: Thu, 25 Apr 2019 10:07:19 +0800 Message-ID: References: <20190421011719.14909-1-baolu.lu@linux.intel.com> <20190421011719.14909-3-baolu.lu@linux.intel.com> <20190422164555.GA31181@lst.de> <0c6e5983-312b-0d6b-92f5-64861cd6804d@linux.intel.com> <20190423061232.GB12762@lst.de> <20190424144532.GA21480@lst.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190424144532.GA21480-jcswGhMUV9g@public.gmane.org> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Christoph Hellwig Cc: kevin.tian-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, mika.westerberg-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, ashok.raj-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, Konrad Rzeszutek Wilk , alan.cox-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, Robin Murphy , iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, pengfei.xu-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, jacob.jun.pan-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, David Woodhouse List-Id: iommu@lists.linux-foundation.org Hi, On 4/24/19 10:45 PM, Christoph Hellwig wrote: > On Tue, Apr 23, 2019 at 03:32:16PM +0800, Lu Baolu wrote: >> When we add the bounce buffer between IOVA and physical buffer, the >> bounced buffer must starts from the same offset in a page, otherwise, >> IOMMU can't work here. > > Why? Even with the odd hardware descriptors typical in Intel land that > only allow offsets in the first page, not the following ones, having > a zero offset where we previously had one should be fine. > This is not VT-d specific. It's just how generic IOMMU works. Normally, IOMMU works in paging mode. So if a driver issues DMA with IOVA 0xAAAA0123, IOMMU can remap it with a physical address 0xBBBB0123. But we should never expect IOMMU to remap 0xAAAA0123 with physical address of 0xBBBB0000. That's the reason why I said that IOMMU will not work there. swiotlb System IOVA bounce page Memory .---------. .---------. .---------. | | | | | | | | | | | | buffer_start .---------. .---------.buffer_start .---------. | |----->| | | | | | | |************>| | | | | | swiotlb | | IOMMU Page '---------' '---------' mapping '---------' Boundary | | | | | | | | | | | | | |----------------------------->| | | | IOMMU mapping | | | | | | IOMMU Page .---------. .---------. Boundary | | | | | | | | | |----------------------------->| | | | IOMMU mapping | | | | | | | | | | IOMMU Page .---------. .---------. .---------. Boundary | | | | | | | | | |************>| | | |----->| | swiotlb | | buffer_end '---------' '---------' mapping '---------' | | | | | | | | | | | | '---------' '---------' '---------' This is the whole view of iommu bounce page. I expect the buffer_start returned by swiotlb_tbl_map_single() starts from the same page_offset as the buffer_start in IOVA. Best regards, Lu Baolu 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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED autolearn=unavailable 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 3531BC282E1 for ; Thu, 25 Apr 2019 02:13:37 +0000 (UTC) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org [140.211.169.12]) (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 0B7C02175B for ; Thu, 25 Apr 2019 02:13:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0B7C02175B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from mail.linux-foundation.org (localhost [127.0.0.1]) by mail.linuxfoundation.org (Postfix) with ESMTP id 915281997; Thu, 25 Apr 2019 02:13:36 +0000 (UTC) Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 73CDC1990 for ; Thu, 25 Apr 2019 02:13:35 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga09.intel.com (mga09.intel.com [134.134.136.24]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id DF11A854 for ; Thu, 25 Apr 2019 02:13:34 +0000 (UTC) X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by orsmga102.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 24 Apr 2019 19:13:34 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,392,1549958400"; d="scan'208";a="340574172" Received: from allen-box.sh.intel.com (HELO [10.239.159.136]) ([10.239.159.136]) by fmsmga006.fm.intel.com with ESMTP; 24 Apr 2019 19:13:31 -0700 Subject: Re: [PATCH v3 02/10] swiotlb: Factor out slot allocation and free To: Christoph Hellwig References: <20190421011719.14909-1-baolu.lu@linux.intel.com> <20190421011719.14909-3-baolu.lu@linux.intel.com> <20190422164555.GA31181@lst.de> <0c6e5983-312b-0d6b-92f5-64861cd6804d@linux.intel.com> <20190423061232.GB12762@lst.de> <20190424144532.GA21480@lst.de> From: Lu Baolu Message-ID: Date: Thu, 25 Apr 2019 10:07:19 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190424144532.GA21480@lst.de> Content-Language: en-US Cc: kevin.tian@intel.com, mika.westerberg@linux.intel.com, ashok.raj@intel.com, Konrad Rzeszutek Wilk , alan.cox@intel.com, Robin Murphy , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, pengfei.xu@intel.com, jacob.jun.pan@intel.com, David Woodhouse X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="UTF-8"; format="flowed" Sender: iommu-bounces@lists.linux-foundation.org Errors-To: iommu-bounces@lists.linux-foundation.org Message-ID: <20190425020719.RxYsaErZzi85ZABLnzF8uHqsuFedDT6bDS8iEw8s1vw@z> Hi, On 4/24/19 10:45 PM, Christoph Hellwig wrote: > On Tue, Apr 23, 2019 at 03:32:16PM +0800, Lu Baolu wrote: >> When we add the bounce buffer between IOVA and physical buffer, the >> bounced buffer must starts from the same offset in a page, otherwise, >> IOMMU can't work here. > > Why? Even with the odd hardware descriptors typical in Intel land that > only allow offsets in the first page, not the following ones, having > a zero offset where we previously had one should be fine. > This is not VT-d specific. It's just how generic IOMMU works. Normally, IOMMU works in paging mode. So if a driver issues DMA with IOVA 0xAAAA0123, IOMMU can remap it with a physical address 0xBBBB0123. But we should never expect IOMMU to remap 0xAAAA0123 with physical address of 0xBBBB0000. That's the reason why I said that IOMMU will not work there. swiotlb System IOVA bounce page Memory .---------. .---------. .---------. | | | | | | | | | | | | buffer_start .---------. .---------.buffer_start .---------. | |----->| | | | | | | |************>| | | | | | swiotlb | | IOMMU Page '---------' '---------' mapping '---------' Boundary | | | | | | | | | | | | | |----------------------------->| | | | IOMMU mapping | | | | | | IOMMU Page .---------. .---------. Boundary | | | | | | | | | |----------------------------->| | | | IOMMU mapping | | | | | | | | | | IOMMU Page .---------. .---------. .---------. Boundary | | | | | | | | | |************>| | | |----->| | swiotlb | | buffer_end '---------' '---------' mapping '---------' | | | | | | | | | | | | '---------' '---------' '---------' This is the whole view of iommu bounce page. I expect the buffer_start returned by swiotlb_tbl_map_single() starts from the same page_offset as the buffer_start in IOVA. Best regards, Lu Baolu _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu