Re: [RFC PATCH v2 12/15] vfio: Support VFIO devices that access the CPU MMU

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Oct 20, 2026 at 12:51:26PM +0100, Ryan Roberts wrote:
> > However.. you still have to affirm which single mm is the mm that the
> > device is going to be doing DMA against. The process the opens the fd
> > should not be forced to be the mm that it gets linked to.
> 
> What is the mm representing here? Ultimately we want to install the KVM
> instance's stage2 pgtables and (pinned) VMID. We currently get that via the
> bound KVM instance (which looks like it still works using the cdev interface?)
> 
> The guest will then install the stage1 pgtables and (pinned) ASID associated
> with the relevant (guest) mm_struct.
> 
> Do we _need_ an mm association in the host?

Ah.. I see, I didn't quite follow that. OK.. Ah everyone else doing
this is using iommufd with a viommu to establish their connection
between device an KVM. eg Jacob Pan's series. That's a probably a
better idea to stay aligned with the common path. Though your reasons
are a little different..

If you manage to get pinned VMID out of KVM then we can implement SMMU
BTM as well!

Jason