From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751439AbeDFCxV (ORCPT ); Thu, 5 Apr 2018 22:53:21 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:57782 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751315AbeDFCxT (ORCPT ); Thu, 5 Apr 2018 22:53:19 -0400 Subject: Re: [RFC] virtio: Use DMA MAP API for devices without an IOMMU To: Benjamin Herrenschmidt , "Michael S. Tsirkin" References: <20180405105631.9514-1-khandual@linux.vnet.ibm.com> <3e1b113b-79ca-b700-5be9-10c66d74aabe@linux.vnet.ibm.com> <20180405175326-mutt-send-email-mst@kernel.org> <1522940983.21446.205.camel@kernel.crashing.org> <20180405213042-mutt-send-email-mst@kernel.org> <1522963113.21446.211.camel@kernel.crashing.org> Cc: robh@kernel.org, aik@ozlabs.ru, jasowang@redhat.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, joe@perches.com, david@gibson.dropbear.id.au, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net From: Anshuman Khandual Date: Fri, 6 Apr 2018 08:23:10 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1 MIME-Version: 1.0 In-Reply-To: <1522963113.21446.211.camel@kernel.crashing.org> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 x-cbid: 18040602-0008-0000-0000-000004E75044 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18040602-0009-0000-0000-00001E7A685E Message-Id: <70cb433f-a8f7-5199-3c96-a760c7624804@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-04-06_02:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1804060027 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/06/2018 02:48 AM, Benjamin Herrenschmidt wrote: > On Thu, 2018-04-05 at 21:34 +0300, Michael S. Tsirkin wrote: >>> In this specific case, because that would make qemu expect an iommu, >>> and there isn't one. >> >> >> I think that you can set iommu_platform in qemu without an iommu. > > No I mean the platform has one but it's not desirable for it to be used > due to the performance hit. Also the only requirement is to bounce the I/O buffers through SWIOTLB implemented as DMA API which the virtio core understands. There is no need for an IOMMU to be involved for the device representation in this case IMHO.