> From: Jason Gunthorpe <j...@nvidia.com> > Sent: Thursday, September 21, 2023 2:20 AM > > On Wed, Sep 20, 2023 at 12:17:24PM -0600, Alex Williamson wrote: > > > > The iommufd design requires one open of the /dev/iommu to be shared > > > across all the vfios. > > > > "requires"? It's certainly of limited value to have multiple iommufd > > instances rather than create multiple address spaces within a single > > iommufd, but what exactly precludes an iommufd per device if QEMU, or > > any other userspace so desired? Thanks, > > From the kernel side requires is too strong I suppose >
Agree. But with limited value let's stay with one iommufd per qemu instance to reduce the maintenance burden. It is also more future-friendly towards nested translation or the need of centralized PASID tracking when supporting SIOV/ENQCMD, etc. Supporting those new features between multiple iommufd's would incur unnecessary complexities.
