Re: [PATCH V3 4/9] iommufd: pfn reader for file mappings

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Oct 04, 2024 at 11:48:15AM -0700, Steve Sistare wrote:

> +static long pin_memfd_pages(struct pfn_reader_user *user, unsigned long start,
> +			    unsigned long npages)
> +{
> +	unsigned long end, nr, i, j, npin, offset, npages_out;
> +	long nfolios;
> +	int rc;
> +	struct folio *folio;
> +	struct page **upages = user->upages;
> +
> +	nfolios = user->ufolios_len / sizeof(*user->ufolios);
> +	end = start + (npages << PAGE_SHIFT) - 1;
> +
> +	nfolios = memfd_pin_folios(user->file, start, end, user->ufolios,
> +				   nfolios, &offset);
> +	if (nfolios <= 0)
> +		return nfolios;
> +
> +	offset >>= PAGE_SHIFT;
> +	npages_out = 0;
> +
> +	for (i = 0; i < nfolios; i++) {
> +		folio = user->ufolios[i];
> +		nr = folio_nr_pages(folio);
> +		npin = min(nr - offset, npages);

What happens if all the folios don't fit into the upages array once
expanded? It looks like they are leaked?

I suppose the later patch gets this all sane, but I wonder if we need
this inbetween step?

Jason