Re: [PATCH v2 1/3] iommufd/viommu: Allow associating a KVM VM fd with a vIOMMU

[Jason Gunthorpe]

On Thu, Mar 12, 2026 at 11:15:16PM -0700, Nicolin Chen wrote:
> On Mon, Mar 09, 2026 at 04:47:02PM +0530, Aneesh Kumar K.V (Arm) wrote:
> > Add optional KVM association to IOMMU_VIOMMU_ALLOC by introducing
> > IOMMU_VIOMMU_KVM_FD and iommu_viommu_alloc::kvm_vm_fd.
> > 
> > When the flag is set, iommufd validates that kvm_vm_fd refers to a KVM
> > VM file and stores a referenced struct file in the vIOMMU object, so
> > later iommufd operations can safely resolve the owning VM.
> > 
> > This is preparatory plumbing for subsequent patches that bind TDI state
> > to the associated KVM VM.
> > 
> > The patch also switch file_is_kvm from EXPORT_SYMBOL_FOR_KVM_INTERNAL to
> > EXPORT_SYMBOL_GPL so that iommu module can use that.
> 
> struct vfio_device has the kvm pointer already. So, I think it
> could be forwarded from VFIO side v.s. via userspace ioctl.
> 
> Shammer had two patches before and Jason partially reviewed. I
> took those for a side project but haven't sent anywhere. Would
> you please check if they for you?
> 
> https://github.com/nicolinc/iommufd/commits/wip/viommu_kvm

That looks pretty reasonable

Raises the point we should not allow mixing kvm pointers, so no matter
what the vfio, idev, viommu all need to agree, and the code should
check that too, eg when associating an idev with a viommu

Jason