Re: [PATCH v2 4/4] coco/tdx-host: Initialize trusted DMA on all capable IOMMUs

[Baolu Lu]

On 10/16/2026 10:58 PM, Jason Gunthorpe wrote:
> On Fri, Oct 16, 2026 at 03:03:23PM +0800, Baolu Lu wrote:
> > On 10/16/2026 1:37 AM, Jason Gunthorpe wrote:
> > > On Thu, Oct 15, 2026 at 04:31:31PM +0800, Xu Yilun wrote:
> > >
> > > > An alternative could be, bringing up one IOMMU when an associated
> > > > device requests link encryption. Then a no-tdx-support iommu fails the
> > > > encryption request naturally.
> > > That is what ARM is planning to do. I think it is reasonable to
> > > trigger creation of the secure iommu when the TSM is connected to TDX.
> > >
> > > Fail connect if the iommu could not be created.
> > Yes, agreed. The Intel iommu driver could use per-device interfaces,
> > just as ARM is planning. There are some differences, though.
> >
> > ARM's interaction with the iommu driver in viommu_init() appears to
> > consist of two steps:
> >
> >   - arm_smmu_get_realm_params(dev, &params): get and validate the
> >     physical iommu information from the arm-smmu-v3 driver;
> >   - cca_psmmu_get(&params): activate the physical smmu for Realm use.
> Okay, I haven't looked, not sure what is in cca_psmmu_get() yet
>
> > So the Intel iommu driver will probably end up with interfaces like:
> >
> >   - dmar_tdxcs_iommu_init(struct device *dev, ...);
> >   - dmar_tdxcs_iommu_release(struct device *dev, ...);
> >
> > These would be called from the connect and disconnect callbacks of
> > the TDX link ops:
> It seems OK
>
> It sounds like you will have a one time init of the secure iommu at
> the time the first PCI device wants to use the TSM? It seems like no
> problem.

Yes.