Re: [PATCH 6/9] iommufd: Have pfn_reader process DMABUF iopt_pages

[Jason Gunthorpe <jgg@nvidia.com>]

On Thu, Nov 20, 2025 at 08:04:37AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Saturday, November 8, 2025 12:50 AM
> > +
> > +static int pfn_reader_fill_dmabuf(struct pfn_reader_dmabuf *dmabuf,
> > +				  struct pfn_batch *batch,
> > +				  unsigned long start_index,
> > +				  unsigned long last_index)
> > +{
> > +	unsigned long start = dmabuf->start_offset + start_index * PAGE_SIZE;
> > +
> > +	/*
> > +	 * This works in PAGE_SIZE indexes, if the dmabuf is sliced and
> > +	 * starts/ends at a sub page offset then the batch to domain code will
> > +	 * adjust it.
> > +	 */
> 
> dmabuf->start_offset comes from pages->dmabuf.start, which is initialized as:
> 
> 	pages->dmabuf.start = start - start_byte;
> 
> so it's always page-aligned. Where is the sub-page offset coming from?

I need to go over this again to check it, this sub-page stuff is
a bit convoluted. start_offset should include the sub page offset
here..

> > @@ -1687,6 +1737,12 @@ static void __iopt_area_unfill_domain(struct
> > iopt_area *area,
> > 
> >  	lockdep_assert_held(&pages->mutex);
> > 
> > +	if (iopt_is_dmabuf(pages)) {
> > +		iopt_area_unmap_domain_range(area, domain, start_index,
> > +					     last_index);
> > +		return;
> > +	}
> > +
> 
> this belongs to patch3?

This is part of programming the domain with the dmabuf, the patch3 was
about the revoke which is a slightly different topic though they are
both similar.

Thanks,
Jason