From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org (bombadil.infradead.org [IPv6:2607:7c80:54:e::133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 41jsqR3BdLzF2D1 for ; Sun, 5 Aug 2018 17:29:39 +1000 (AEST) Date: Sun, 5 Aug 2018 00:29:30 -0700 From: Christoph Hellwig To: Benjamin Herrenschmidt Cc: Christoph Hellwig , "Michael S. Tsirkin" , Will Deacon , Anshuman Khandual , virtualization@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, aik@ozlabs.ru, robh@kernel.org, joe@perches.com, elfring@users.sourceforge.net, david@gibson.dropbear.id.au, jasowang@redhat.com, mpe@ellerman.id.au, linuxram@us.ibm.com, haren@linux.vnet.ibm.com, paulus@samba.org, srikar@linux.vnet.ibm.com, robin.murphy@arm.com, jean-philippe.brucker@arm.com, marc.zyngier@arm.com Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Message-ID: <20180805072930.GB23288@infradead.org> References: <20180802200646-mutt-send-email-mst@kernel.org> <20180802225738-mutt-send-email-mst@kernel.org> <20180803070507.GA1344@infradead.org> <20180803160246.GA13794@infradead.org> <22310f58605169fe9de83abf78b59f593ff7fbb7.camel@kernel.crashing.org> <20180804082120.GB4421@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Sun, Aug 05, 2018 at 11:10:15AM +1000, Benjamin Herrenschmidt wrote: > - One you have rejected, which is to have a way for "no-iommu" virtio > (which still doesn't use an iommu on the qemu side and doesn't need > to), to be forced to use some custom DMA ops on the VM side. > > - One, which sadly has more overhead and will require modifying more > pieces of the puzzle, which is to make qemu uses an emulated iommu. > Once we make qemu do that, we can then layer swiotlb on top of the > emulated iommu on the guest side, and pass that as dma_ops to virtio. Or number three: have a a virtio feature bit that tells the VM to use whatever dma ops the platform thinks are appropinquate for the bus it pretends to be on. Then set a dma-range that is limited to your secure memory range (if you really need it to be runtime enabled only after a device reset that rescans) and use the normal dma mapping code to bounce buffer.