From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [RFC 0/4] Virtio uses DMA API for all devices Date: Sun, 5 Aug 2018 00:29:30 -0700 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" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: 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: Benjamin Herrenschmidt Cc: robh@kernel.org, srikar@linux.vnet.ibm.com, "Michael S. Tsirkin" , mpe@ellerman.id.au, Will Deacon , linux-kernel@vger.kernel.org, linuxram@us.ibm.com, virtualization@lists.linux-foundation.org, Christoph Hellwig , paulus@samba.org, marc.zyngier@arm.com, joe@perches.com, robin.murphy@arm.com, david@gibson.dropbear.id.au, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, haren@linux.vnet.ibm.com, Anshuman Khandual List-Id: virtualization@lists.linuxfoundation.org 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.