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

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Date:   Tue, 3 Apr 2018 11:47:34 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Oleksandr Andrushchenko <andr2000@...il.com>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, airlied@...ux.ie,
        daniel.vetter@...el.com, seanpaul@...omium.org,
        gustavo@...ovan.org, jgross@...e.com, boris.ostrovsky@...cle.com,
        konrad.wilk@...cle.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [PATCH 1/1] drm/xen-zcopy: Add Xen zero-copy helper DRM driver

On Thu, Mar 29, 2018 at 04:19:31PM +0300, Oleksandr Andrushchenko wrote:
> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.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.

And you probably want to check this at import/attach time.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch