Re: [RFC PATCH v4 03/16] iommu/arm-smmu-v3: Add initial pSMMU realm viommu plumbing

From: Baolu Lu

Date: Fri Sep 18 2026 - 01:54:28 EST

On 9/16/2026 8:39 PM, Jason Gunthorpe wrote:
On Wed, Sep 16, 2026 at 05:54:57AM +0000, Tian, Kevin wrote:
At least for ARM there is effectively no entanglement with the actual
host iommu driver. The viommu is entirely provided by software in the
RMM world, so it can have its own dedicated driver. In ARM T=1
transactions are alwayus routed to the RMM's iommu and there is no
relation to the host.

I am interested how Intel works here, but I thought it was similar.
Largely yes. Main difference at Intel side is that TDX still relies on the
host to initiate iotlb invalidation (upon notification from KVM on S-EPT
change). Currently we put this logic in intel-iommu driver but it's more
about wrapping invalidation info and passing it to the firmware. Moving
it into the tsm driver should be straightforward.

Maybe there'll be other subtle connections to host iommu driver but
it doesn't sound a hard problem to solve.
Okay, so I saw the driver posting for basic iommu support, can we try
to rework that to be split out like Aneesh is doing so everything
about TDX calls lives in tsm and intel iommu only provides a small API
surface to exchange whatever details are needed to bootstrap TDX
module?

Are you referring to this series?

https://lore.kernel.org/linux-iommu/20260915074235.1219183-1-baolu.lu@xxxxxxxxxxxxxxx/

It initializes the iommu managed by the secure world (the TDX module).

I’m happy to rework it as you suggested by moving most of the TDX-
related code into the tsm driver and leaving the host iommu driver to
provide only the necessary assistance.

Thanks,
baolu