On Fri, Feb 07, 2025 at 12:21:54PM +0000, Shameerali Kolothum Thodi wrote: > Just wondering whether we can have something like the > vfio_register_iommu_driver() for iommufd subsystem by which it can directly > access iommu drivers ops(may be a restricted set).
I very much want to try hard to avoid that. AFAICT you do not need a VFIO device, or access to the HW_INFO of the smmu to start up a SMMU driver. Yes, you cannot later attach a VFIO device with a pSMMU that materially differs from vSMMU setup, but that is fine. qemu has long had a duality where you can either "inherit from host" for an easy setup or be "fully specified" and support live migration/etc. CPUID as a simple example. So, what the smmu patches are doing now is "inherit from host" and that requires a VFIO device to work. I think that is fine. If you want to do full hotplug then you need to "fully specified" on the command line so a working vSMMU can be shown to the guest with no devices, and no kernel involvement. Obviously this is a highly advanced operating mode as things like IIDR and errata need to be considered, but I would guess booting with no vPCI devices is already abnormal. Jason
