linux-kernel - Re: [PATCH 8/9] drm/xen-front: Implement GEM operations

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Date:   Fri, 23 Feb 2018 10:26:56 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Oleksandr Andrushchenko <andr2000@...il.com>,
        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, konrad.wilk@...cle.com
Cc:     Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: Re: [PATCH 8/9] drm/xen-front: Implement GEM operations

On 02/21/2018 03:03 AM, Oleksandr Andrushchenko wrote:
> +static struct xen_gem_object *gem_create(struct drm_device *dev, size_t size)
> +{
> +	struct xen_drm_front_drm_info *drm_info = dev->dev_private;
> +	struct xen_gem_object *xen_obj;
> +	int ret;
> +
> +	size = round_up(size, PAGE_SIZE);
> +	xen_obj = gem_create_obj(dev, size);
> +	if (IS_ERR_OR_NULL(xen_obj))
> +		return xen_obj;
> +
> +	if (drm_info->cfg->be_alloc) {
> +		/*
> +		 * backend will allocate space for this buffer, so
> +		 * only allocate array of pointers to pages
> +		 */
> +		xen_obj->be_alloc = true;

If be_alloc is a flag (which I am not sure about) --- should it be set
to true *after* you've successfully allocated your things?

> +		ret = gem_alloc_pages_array(xen_obj, size);
> +		if (ret < 0) {
> +			gem_free_pages_array(xen_obj);
> +			goto fail;
> +		}
> +
> +		ret = alloc_xenballooned_pages(xen_obj->num_pages,
> +				xen_obj->pages);

Why are you allocating balloon pages?

-boris

> +		if (ret < 0) {
> +			DRM_ERROR("Cannot allocate %zu ballooned pages: %d\n",
> +					xen_obj->num_pages, ret);
> +			goto fail;
> +		}
> +
> +		return xen_obj;
> +	}
> +	/*
> +	 * need to allocate backing pages now, so we can share those
> +	 * with the backend
> +	 */
> +	xen_obj->num_pages = DIV_ROUND_UP(size, PAGE_SIZE);
> +	xen_obj->pages = drm_gem_get_pages(&xen_obj->base);
> +	if (IS_ERR_OR_NULL(xen_obj->pages)) {
> +		ret = PTR_ERR(xen_obj->pages);
> +		xen_obj->pages = NULL;
> +		goto fail;
> +	}
> +
> +	return xen_obj;
> +
> +fail:
> +	DRM_ERROR("Failed to allocate buffer with size %zu\n", size);
> +	return ERR_PTR(ret);
> +}
> +
>