Re: [RFC 00/18] vfio: Adopt iommufd

On Tue, Apr 26, 2022 at 10:21:59AM -0600, Alex Williamson wrote: > We also need to be able to advise libvirt as to how each iommufd object > or user of that object factors into the VM locked memory requirement. > When used by vfio-pci, we're only mapping VM RAM, so we'd ask libvirt > to set the locked memory limit to the size of VM RAM per iommufd, > regardless of the number of devices using a given iommufd. However, I > don't know if all users of iommufd will be exclusively mapping VM RAM. > Combinations of devices where some map VM RAM and others map QEMU > buffer space could still require some incremental increase per device > (I'm not sure if vfio-nvme is such a device). It seems like heuristics > will still be involved even after iommufd solves the per-device > vfio-pci locked memory limit issue. Thanks, If the model is to pass the FD, how about we put a limit on the FD itself instead of abusing the locked memory limit? We could have a no-way-out ioctl that directly limits the # of PFNs covered by iopt_pages inside an iommufd.