Hi Peter, On 12/8/22 00:49, Peter Xu wrote: > 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.
I don't think it can race because a mutex is hold while doing the virtio_iommu_replay(), and each time a virtio cmd is handled (attach, map, unmap), see virtio_iommu_handle_command. So I think it is safe. Thanks Eric > > 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, >
