On Tue, Jan 21, 2020 at 12:00:57PM +0800, Jason Wang wrote: > > On 2020/1/21 上午1:49, 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. > > > I think in this case, you meant the method proposed by Shahaf that sends > diffs of "fixed translation" to device? > > It would be kind of tricky to deal with the following case for example: > > old map [4G, 16G) new map [4G, 8G) > > If we do > > 1) flush [4G, 16G) > 2) add [4G, 8G) > > There could be a window between 1) and 2). > > It requires the IOMMU that can do > > 1) remove [8G, 16G) > 2) flush [8G, 16G) > 3) change [4G, 8G) > > .... Basically what I had in mind is something like qemu memory api 0. begin 1. remove [8G, 16G) 2. add [4G, 8G) 3. commit Anyway, I'm fine with a one-shot API for now, we can improve it later. > > > > 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 > > > Or I wonder whether ATS/PRI can help here. E.g during I/O page fault, > driver/device can wait for the new mapping to be set and then replay the > DMA. > > Thanks > -- MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
