On 24/09/2015 06:33, David Gibson wrote: > When we have guest visible IOMMUs, we allow notifiers to be registered > which will be informed of all changes to IOMMU mappings. This is used by > vfio to keep the host IOMMU mappings in sync with guest IOMMU mappings. > > However, unlike with a memory region listener, an iommu notifier won't be > told about any mappings which already exist in the (guest) IOMMU at the > time it is registered. This can cause problems if hotplugging a VFIO > device onto a guest bus which had existing guest IOMMU mappings, but didn't > previously have an VFIO devices (and hence no host IOMMU mappings). > > This adds a memory_region_register_iommu_notifier_replay() function to > handle this case. As well as registering the new notifier it replays > existing mappings. Because the IOMMU memory region doesn't internally > remember the granularity of the guest IOMMU it has a small hack where the > caller must specify a granularity at which to replay mappings. > > If there are finer mappings in the guest IOMMU these will be reported in > the iotlb structures passed to the notifier which it must handle (probably > causing it to flag an error). This isn't new - the VFIO iommu notifier > must already handle notifications about guest IOMMU mappings too short > for it to represent in the host IOMMU. > > Signed-off-by: David Gibson <da...@gibson.dropbear.id.au>
The patch is okay, just two questions: 1) Is there a case where using the no-replay functions makes sense? 2) You could add a ->replay function to the iommu_ops to optimize it, if you want. Paolo
