Messages in this thread | | | Date | Mon, 9 Apr 2018 10:27:40 +0200 | From | Daniel Vetter <> | Subject | Re: [PATCH 1/1] drm/xen-zcopy: Add Xen zero-copy helper DRM driver |
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On Fri, Apr 06, 2018 at 02:25:08PM +0300, Oleksandr Andrushchenko wrote: > 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?
Yes.
> What are the other use-cases for that to happen?
Sharing vram or other resources which are not backed by a struct page. See Christian König's recent work to accomplish just that for admgpu.
> > 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?
Yup.
> > -Daniel > Thank you, > Oleksandr
Cheers, Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
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