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...t; > for all virtio devices). > > From all that I've gather so far: no you do not want that. We really > need to figure out virtio "dma" interacts with the host / device. > > If you look at the current iommu spec it does talk of physical address > with a little careveout for VIRTIO_F_IOMMU_PLATFORM. That's true, although that doesn't exist in the legacy virtio spec, and we have an existing emulation platform which puts legacy virtio devices behind an IOMMU. Currently, Linux is unable to boot on this platform unless the IOMMU is configured as bypass. If we...

On Tue, Jul 31, 2018 at 03:36:22PM -0500, Benjamin Herrenschmidt wrote: > On Tue, 2018-07-31 at 10:30 -0700, Christoph Hellwig wrote: > > > However the question people raise is that DMA API is already full of > > > arch-specific tricks the likes of which are outlined in your post linked > > > above. How is this one much worse? > > > > None of these warts

On Tue, Jul 31, 2018 at 03:36:22PM -0500, Benjamin Herrenschmidt wrote: > On Tue, 2018-07-31 at 10:30 -0700, Christoph Hellwig wrote: > > > However the question people raise is that DMA API is already full of > > > arch-specific tricks the likes of which are outlined in your post linked > > > above. How is this one much worse? > > > > None of these warts

...tion platforms have an IOMMU > for all virtio devices). >From all that I've gather so far: no you do not want that. We really need to figure out virtio "dma" interacts with the host / device. If you look at the current iommu spec it does talk of physical address with a little careveout for VIRTIO_F_IOMMU_PLATFORM. So between that and our discussion in this thread and its previous iterations I think we need to stick to the current always physical, bypass system dma ops mode of virtio operation as the default. We just need to figure out how to deal with devices that deviate from...