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

Tian, Kevin
2023-03-02T08:06:35Z

> 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.