On Wed, Feb 12, 2025 at 08:50:07AM -0400, Jason Gunthorpe wrote: > On Tue, Feb 11, 2025 at 04:41:51PM -0800, Jacob Pan wrote: > > > I see the same on arm64 with v9.0, assigned an ixgbe nic via VFIO. > > Huh, I figured it worked on ARM.. Crosvm would be a more useful test because it doesn't implement any BYPASS feature, but I don't have it set up at the moment. It's not a problem on QEMU since it supports the BYPASS feature and doesn't need identity-mapped domains. > > There is no requirement that an iommu driver implement identity, this > is all an optimization. If it doesn't work in alot of cases can we > just remove it? It would simplfy a lot.. No objection. Identity domains are useful if the use-case of virtio-iommu is assigning devices to guest userspace, in which case you'd want to bypass the IOMMU for the devices that are still owned by the kernel. But VMMs have at least two alternatives to identity-mapping (BYPASS feature and tailored topology). Thanks, Jean
