From mboxrd@z Thu Jan 1 00:00:00 1970 From: Benjamin Herrenschmidt Subject: Re: [RFC] virtio: Use DMA MAP API for devices without an IOMMU Date: Fri, 06 Apr 2018 07:18:33 +1000 Message-ID: <1522963113.21446.211.camel@kernel.crashing.org> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20180405213042-mutt-send-email-mst@kernel.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org To: "Michael S. Tsirkin" Cc: robh@kernel.org, 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, Anshuman Khandual List-Id: virtualization@lists.linuxfoundation.org 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. Cheers, Ben. > > > Anshuman, you need to provide more background here. I don't have time > > right now it's late, but explain about the fact that this is for a > > specific type of secure VM which has only a limited pool of (insecure) > > memory that can be shared with qemu, so all IOs need to bounce via that > > pool, which can be achieved by using swiotlb. > > > > Note: this isn't urgent, we can discuss alternative approaches, this is > > just to start the conversation. > > > > Cheers, > > Ben.