On Tue, 20 Oct 2026 16:06:37 +0100 Ryan Roberts <[email protected]> wrote:
> On 20/10/2026 15:09, Jason Gunthorpe wrote: > > 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.. > > Just to check, you're referring to [1]? > > I was under the impression that I could open the VFIO device through the cdev > interface, then bind it to the KVM instance via KVM_DEV_VFIO_FILE_ADD... Why > do > I need an iommufd at all? The cdev is not unlocked to actually access the device until it's bound to iommufd. Thanks, Alex
