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

[Jason Gunthorpe]

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.

Jason