On Wed, Jan 21, 2026 at 05:24:28PM -0800, Nicolin Chen wrote:

VMM needs a domain holding the mappings between gPA to hPA. It can be an S1
domain or an S2 nesting parent domain, depending on whether the VM is built
with a vSMMU or not.

Given that the IOAS for this gPA mapping is the same across SMMU instances,
this domain can be shared across devices even if they sit behind different
SMMUs, so long as the underlying page table is compatible between the SMMU
instances.

There is no direct information about the page table from the master device,
but a comparison can be done between the physical SMMU that the domain was
allocated for and the physical SMMU that the device is behind.

I would very much prefer this works by inspecting the cfg from the
iopgtable..

You can get it by doing 

	struct io_pgtable_cfg *pgtbl_cfg =
		&io_pgtable_ops_to_pgtable(domain->pgtbl_ops)->cfg;

I think it is important that the domain->smmu pointer be removed as
well

Jason