On Thu, Mar 28, 2019 at 11:54:02AM -0500, Shiraz Saleem wrote:
> +/* ib_umem_add_sg_table - Add N contiguous pages to scatter table
> + *
> + * sg: current scatterlist entry
> + * page_list: array of npage struct page pointers
> + * npages: number of pages in page_list
> + * nents: [out] number of entries in the scatterlist
> + *
> + * Return new end of scatterlist
> + */
> +static struct scatterlist *ib_umem_add_sg_table(struct scatterlist *sg,
> + struct page **page_list,
> + unsigned long npages,
> + int *nents)
> +{
> + unsigned long first_pfn;
> + unsigned long i = 0;
> + bool update_cur_sg = false;
> + bool first = !sg_page(sg);
> +
> + /* Check if new page_list is contiguous with end of previous page_list.
> + * sg->length here is a multiple of PAGE_SIZE and sg->offset is 0.
> + */
> + if (!first && (page_to_pfn(sg_page(sg)) + (sg->length >> PAGE_SHIFT) ==
> + page_to_pfn(page_list[0])))
> + update_cur_sg = true;
> +
> + while (i != npages) {
> + unsigned long len;
> + struct page *first_page = page_list[i];
> +
> + first_pfn = page_to_pfn(first_page);
> +
> + /* Compute the number of contiguous pages we have starting
> + * at i
> + */
> + for (len = 0; i != npages &&
> + first_pfn + len == page_to_pfn(page_list[i]);
> + len++)
> + i++;
> +
> + /* Squash N contiguous pages from page_list into current sge */
> + if (update_cur_sg) {
> + sg_set_page(sg, sg_page(sg),
> + sg->length + (len << PAGE_SHIFT), 0);
There is another problem here.. The sg->length is an 'unsigned int' so
this add can technically overflow. Need to also check 'if length +
len > UINT_MAX' before combining.
There is also dma_get_max_seg_size(), maybe that is the right limit?
Maybe the IB core should just call dma_set_max_seg_size(2G) for all
drivers?
I'm looking at the iommu code and thinking if you pass a sg->length >
max_seg_size it probably does something bad ..
Jason
