Re: [PATCH 2/6] iommupt: allow full-table contiguous leaves in unit tests

[Jason Gunthorpe]

On Sun, Jul 12, 2026 at 10:18:52PM +0100, Daniel Drake wrote:
> The generic_pt tests currently assume that a format should never support
> a contiguous page size that spans the entire mapping range of the table
> it resides in.
> 
> This assumption breaks for BCM2712, which has a 2-level page table.
> Level 1 entries cover 4MB of memory via their corresponding Level 0
> table pages. There is a concept of a 4MB largepage, but that is
> represented as a Level 1 entry pointing at a Level 0 table with the 1024
> usual PTEs with an additional largepage hint applied (for TLB
> optimization purposes). Unlike typical IOMMUs, it is not possible to have
> the Level 1 entry point directly at a 4MB chunk without the need for
> Level 0 mapping.
> 
> This BCM2712 format is well supported by generic_pt: SZ_4M can be
> advertised as a possible size at Level 0 (so that the iommu core feeds
> it 4MB-aligned mapping requests where possible), and drivers can also
> advertise that *all* leaf entries are installed at Level 0. This indicates
> that the tests are overly strict.
> 
> Transform the test to become a validation of the driver's routing intent:
> for every advertised page size, check that pt_pgsz_lg2_to_level() maps that
> size back to the table level under test. This is roughly what the original
> tests were doing, but also allows the BCM2712 case to pass.

Seems fine, but I wonder if it should be conditional on the format
somehow, I put it in to detect mistakes on what was the universal case
that nothing would do this.

Either way

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

Jason