Hi, Eric, On Wed, Dec 07, 2022 at 02:36:44PM +0100, Eric Auger wrote: > When assigning VFIO devices protected by a virtio-iommu we need to replay > the mappings when adding a new IOMMU MR and when attaching a device to > a domain. While we do a "remap" we currently fail to first unmap the > existing IOVA mapping and just map the new one. With some device/group > topology this can lead to errors in VFIO when trying to DMA_MAP IOVA > ranges onto existing ones.
I'm not sure whether virtio-iommu+vfio will suffer from DMA races like when we were working on the vt-d replay for vfio. The issue is whether DMA can happen right after UNMAP but before MAP of the same page if the page was always mapped. The vt-d resolved it by using iova_tree so in a replay vt-d knows the page didn't change, so it avoids unmap+map. It only notifies newly unmapped or newly mapped. Thanks, -- Peter Xu
