From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from gate.crashing.org (gate.crashing.org [63.228.1.57]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 415S4H4zB7zDrcd for ; Wed, 13 Jun 2018 23:18:23 +1000 (AEST) Message-ID: <10bbd7122aaa67f51de7a8328df8154212a13f23.camel@kernel.crashing.org> Subject: Re: [RFC V2] virtio: Add platform specific DMA API translation for virito devices From: Benjamin Herrenschmidt To: Christoph Hellwig Cc: Ram Pai , "Michael S. Tsirkin" , robh@kernel.org, pawel.moll@arm.com, Tom Lendacky , aik@ozlabs.ru, jasowang@redhat.com, cohuck@redhat.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, joe@perches.com, "Rustad, Mark D" , david@gibson.dropbear.id.au, linuxppc-dev@lists.ozlabs.org, elfring@users.sourceforge.net, Anshuman Khandual Date: Wed, 13 Jun 2018 23:11:01 +1000 In-Reply-To: <5dbcafa73b065bc619fd6adc9ef47eb6367b8378.camel@kernel.crashing.org> References: <20180522063317.20956-1-khandual@linux.vnet.ibm.com> <20180523213703-mutt-send-email-mst@kernel.org> <20180524072104.GD6139@ram.oc3035372033.ibm.com> <0c508eb2-08df-3f76-c260-90cf7137af80@linux.vnet.ibm.com> <20180531204320-mutt-send-email-mst@kernel.org> <20180607052306.GA1532@infradead.org> <20180607185234-mutt-send-email-mst@kernel.org> <20180611023909.GA5726@ram.oc3035372033.ibm.com> <07b804fccd7373c650be79ac9fa77ae7f2375ced.camel@kernel.crashing.org> <20180613074141.GA12033@infradead.org> <5dbcafa73b065bc619fd6adc9ef47eb6367b8378.camel@kernel.crashing.org> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2018-06-13 at 22:25 +1000, Benjamin Herrenschmidt wrote: > On Wed, 2018-06-13 at 00:41 -0700, Christoph Hellwig wrote: > > On Mon, Jun 11, 2018 at 01:29:18PM +1000, Benjamin Herrenschmidt wrote: > > > At the risk of repeating myself, let's just do the first pass which is > > > to switch virtio over to always using the DMA API in the actual data > > > flow code, with a hook at initialization time that replaces the DMA ops > > > with some home cooked "direct" ops in the case where the IOMMU flag > > > isn't set. > > > > > > This will be equivalent to what we have today but avoids having 2 > > > separate code path all over the driver. > > > > > > Then a second stage, I think, is to replace this "hook" so that the > > > architecture gets a say in the matter. > > > > I don't think we can actually use dma_direct_ops. It still allows > > architectures to override parts of the dma setup, which virtio seems > > to blindly assume phys == dma and not cache flushing. > > By direct ops I didn't mean *the* dma_direct_ops but a virtio-local > variants that effectively reproduces the existing expectations (ie, > virtio-dma-legacy-ops or something). Actually ... the stuff in lib/dma-direct.c seems to be just it, no ? There's no cache flushing and there's no architecture hooks that I can see other than the AMD security stuff which is probably fine. Or am I missing something ? Cheers, Ben. > > > I think the right way forward is to either add a new > > VIRTIO_F_IS_PCI_DEVICE (or redefine the existing iommu flag if deemed > > possible). And then make sure recent qemu always sets it. > > Ben.