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 03:06:07PM -0300, Jason Gunthorpe wrote:
>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

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.
>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.
>
>Thanks,
>Jason

No change needed. Putting this here again:

Reviewed-by: Samiullah Khawaja <skhawaja@google.com>

Thanks,
Sami