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

[Samiullah Khawaja <skhawaja@google.com>]

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?
>>		map.leaf_pgsize_lg2 = PAGE_SHIFT;
>>-- 
>>2.43.0
>>
>
>Reviewed-by: Samiullah Khawaja <skhawaja@google.com>