Re: EBUSY when using NVMe Block Driver with multiple devices in the same IOMMU group

[Chaitanya Kulkarni]

> First, multiple QEMU instances cannot access nvme:// devices sharing the
> same IOMMU group. I don't think this will ever be possible because it
> opens a backdoor around process memory isolation.
> 
> However, a single QEMU (or qemu-storage-daemon) instance should be able
> to access multiple nvme:// devices in the same IOMMU group.
> Unfortunately the code currently doesn't support that.
> util/vfio-helpers.c:qemu_vfio_init_pci() has no logic for sharing
> groups/containers. Opening the group fails with EBUSY because the kernel
> only allows the file to be opened once at any given time.
> 
> It's possible to extend the util/vfio-helpers.c code to reuse VFIO
> groups (and share VFIO containers), but I'm not aware of anyone who is
> currently working on that.
> 
> Stefan

Thanks a lot for detailed explanation, it is really helpful.

-ck