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[209.132.180.67]) by mx.google.com with ESMTP id t2si32120333plq.56.2019.04.28.22.17.28; Sun, 28 Apr 2019 22:17:43 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727079AbfD2FQh (ORCPT + 99 others); Mon, 29 Apr 2019 01:16:37 -0400 Received: from mga03.intel.com ([134.134.136.65]:29193 "EHLO mga03.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725468AbfD2FQh (ORCPT ); Mon, 29 Apr 2019 01:16:37 -0400 X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by orsmga103.jf.intel.com with ESMTP/TLS/DHE-RSA-AES256-GCM-SHA384; 28 Apr 2019 22:16:37 -0700 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.60,408,1549958400"; d="scan'208";a="295363562" Received: from allen-box.sh.intel.com (HELO [10.239.159.136]) ([10.239.159.136]) by orsmga004.jf.intel.com with ESMTP; 28 Apr 2019 22:16:34 -0700 Cc: baolu.lu@linux.intel.com, David Woodhouse , Joerg Roedel , ashok.raj@intel.com, jacob.jun.pan@intel.com, alan.cox@intel.com, kevin.tian@intel.com, mika.westerberg@linux.intel.com, pengfei.xu@intel.com, Konrad Rzeszutek Wilk , Marek Szyprowski , Robin Murphy , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org 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> <20190426150433.GA19930@lst.de> From: Lu Baolu Message-ID: <93b3d627-782d-cae0-2175-77a5a8b3fe6e@linux.intel.com> Date: Mon, 29 Apr 2019 13:10:17 +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: <20190426150433.GA19930@lst.de> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Christoph, On 4/26/19 11:04 PM, Christoph Hellwig wrote: > On Thu, Apr 25, 2019 at 10:07:19AM +0800, Lu Baolu wrote: >> 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. > > Well, with the iommu it doesn't happen. With swiotlb it obviosuly > can happen, so drivers are fine with it. Why would that suddenly > become an issue when swiotlb is called from the iommu code? > I would say IOMMU is DMA remapping, not DMA engine. :-) Best regards, Lu Baolu