On Mon, Jan 20, 2020 at 04:43:53PM +0800, Jason Wang wrote: > This is similar to the design of platform IOMMU part of vhost-vdpa. We > decide to send diffs to platform IOMMU there. If it's ok to do that in > driver, we can replace set_map with incremental API like map()/unmap(). > > Then driver need to maintain rbtree itself. I think we really need to see two modes, one where there is a fixed translation without dynamic vIOMMU driven changes and one that supports vIOMMU. There are different optimization goals in the drivers for these two configurations. > > If the first one, then I think memory hotplug is a heavy flow > > regardless. Do you think the extra cycles for the tree traverse > > will be visible in any way? > > I think if the driver can pause the DMA during the time for setting up new > mapping, it should be fine. This is very tricky for any driver if the mapping change hits the virtio rings. :( Even a IOMMU using driver is going to have problems with that.. Jason
