RE: [PATCH 04/14] iommufd: Use the iommufd_group to avoid duplicate reserved groups and msi setup

From: Jason Gunthorpe jgg@nvidia.com Sent: Saturday, February 25, 2023 8:28 AM

These items only needs to be done once per group, not once per device. The once per device was a way to make the device list work. Since we are abandoning this we can optimize things a bit.

Are we sure that a device hot-plugged into the group won't increase the list of reserved IOVA ranges?

Currently iommu_get_group_resv_regions() queries reserved regions per device and then merge them into the specified list.

Of course VFIO cannot cope with it since its group_attach() is done only once. But if such scenario does exist then the current per-device reservation in iommufd looks an improvement.