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 05:57:13PM +0000, Samiullah Khawaja wrote:
> On Wed, May 13, 2026 at 05:46:22PM +0000, Samiullah Khawaja wrote:
> > On Tue, May 12, 2026 at 01:46:16PM -0300, Jason Gunthorpe wrote:
> > > Sashiko pointed out that the driver could drop PAGE_SIZE from the
> > > pgsize_bitmap. That is technically allowed but nothing does it, and
> > > such an iommu_domain would not be used with the DMA API today.
> > > 
> > > Still, it is against the design and it is trivial to fix up. Lift
> > > the PT_WARN_ON to the if branch and just skip the fast path.
> > > 
> > > Fixes: dcd6a011a8d5 ("iommupt: Add map_pages op")
> > > Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
> > > ---
> > > drivers/iommu/generic_pt/iommu_pt.h | 4 ++--
> > > 1 file changed, 2 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/drivers/iommu/generic_pt/iommu_pt.h b/drivers/iommu/generic_pt/iommu_pt.h
> > > index 19b6daf88f2ab1..4877b05291c9d4 100644
> > > --- a/drivers/iommu/generic_pt/iommu_pt.h
> > > +++ b/drivers/iommu/generic_pt/iommu_pt.h
> > > @@ -920,8 +920,8 @@ static int NS(map_range)(struct pt_iommu *iommu_table, dma_addr_t iova,
> > > 		return ret;
> > > 
> > > 	/* Calculate target page size and level for the leaves */
> > > -	if (pt_has_system_page_size(common) && len == PAGE_SIZE) {
> > > -		PT_WARN_ON(!(pgsize_bitmap & PAGE_SIZE));
> > > +	if (pt_has_system_page_size(common) && len == PAGE_SIZE &&
> > > +		likely(pgsize_bitmap & PAGE_SIZE)) {
> > > 		if (log2_mod(iova | paddr, PAGE_SHIFT))
> > > 			return -ENXIO;
> 
> After thought nit:
> 
> 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
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().

Thanks,
Jason