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

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@xxxxxxxx>
+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?
Thank you,

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