Re: [PATCH 1/1] drm/xen-zcopy: Add Xen zero-copy helper DRM driver

Oleksandr Andrushchenko
2018-04-06T11:25:43Z

On 04/03/2018 12:47 PM, Daniel Vetter wrote:
> On Thu, Mar 29, 2018 at 04:19:31PM +0300, Oleksandr Andrushchenko wrote:
>> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
>> +static int to_refs_grant_foreign_access(struct xen_gem_object *xen_obj)
>> +{
>> + grant_ref_t priv_gref_head;
>> + int ret, j, cur_ref, num_pages;
>> + struct sg_page_iter sg_iter;
>> +
>> + ret = gnttab_alloc_grant_references(xen_obj->num_pages,
>> + &priv_gref_head);
>> + if (ret < 0) {
>> + DRM_ERROR("Cannot allocate grant references\n");
>> + return ret;
>> + }
>> +
>> + j = 0;
>> + num_pages = xen_obj->num_pages;
>> + for_each_sg_page(xen_obj->sgt->sgl, &sg_iter, xen_obj->sgt->nents, 0) {
>> + struct page *page;
>> +
>> + page = sg_page_iter_page(&sg_iter);
> Quick drive-by: You can't assume that an sgt is struct page backed.
Do you mean that someone could give me sgt which never
seen sg_assign_page for its entries?
What are the other use-cases for that to happen?
> And you probably want to check this at import/attach time.
The check you mean is to make sure that when I call
page = sg_page_iter_page(&sg_iter);
I have to make sure that I get a valid page?
> -Daniel
Thank you,
Oleksandr