Presumably w-bits (aw-bits?) implies using intel-iommu, there's a opportunity for the vfio iommu backend to return -ENOSPC (-28) if we exceed the default number of in-flight DMA mappings per container. The default limit is 65535. You can try increasing this by changing the dma_entry_limit module option on the vfio_iommu_type1 module. Note that in a typical vIOMMU config there's a container per device, so the number of VFs attached is possibly not a factor. It is however a lot of DMA mappings for a single device if this is the issue and you'd generally want to boot the guest with iommu=pt in order to have reasonable assigned device performance with a vIOMMU, which would also greatly reduce the number of mappings.
-- You received this bug notification because you are a member of qemu- devel-ml, which is subscribed to QEMU. https://bugs.launchpad.net/bugs/1851664 Title: qemu-system-x86_64: "VFIO_MAP_DMA : -28" error when we attache 6 VF's to guest machine Status in QEMU: Incomplete Bug description: We are trying to attach 6 VF's to the guest machine on 4.1.1 qemu emulator. We are observing "VFIO_MAP_DMA : -28" error. We are using w-bits=48 bits while lunching VM. To manage notifications about this bug go to: https://bugs.launchpad.net/qemu/+bug/1851664/+subscriptions
