Re: [PATCH rc 4/5] iommupt: Check for missing PAGE_SIZE in the pgsize_bitmap

[Jason Gunthorpe <jgg@nvidia.com>]

On Wed, May 13, 2026 at 06:48:26PM +0000, Samiullah Khawaja wrote:
> > > I wonder if the error handling of iova and paddr alignment should also
> > > be deferred to non-fast path? Basically lift the iova and paddr check
> > > in the parent if?
> > 
> > That would break support for < PAGE_SIZE tables which I've tried to
> 
> I was also thinking about support of < PAGE_SIZE tables and wondering
> whether the < PAGE_SIZE tables support is already broken. For examples
> consider following:
> 
> iova = 0x12341800
> paddr = 0x56781800
> len = PAGE_SIZE (4k)
> 
> But pt_has_system_page_size() will be false in such a system.

Yeah, it will be false so it skips that branch. The main code should
be fine and it is covered by the kunit on the 64k arm systems, and the
iommufd self tests on all systems

> > keep generic support for. Similar checks already exist in the generic
> > code in a more general way, probably the first is
> > pt_compute_best_pgsize().
> 
> I was suggesting to rely on the already existing checks in
> pt_compute_best_pgsize() to do error handling, by only entering fast
> path if iova and paddr are also aligned.

When I wrote it didn't think there was a way to trigger it falsely, I
wonder if that wrong.

Yes, it would be easier to think about if it falls through to the slow
path.

Jason