On Mon, Jan 20, 2020 at 05:49:39PM +0000, Jason Gunthorpe wrote: > 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 I think for starters we can assume this doesn't happen, so any change doesn't affect any buffers in use. Certainly true e.g. for memory hotplug. -- MST
