On 02/23/2018 05:26 PM, Boris Ostrovsky wrote:
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?
this is a configuration option telling about the way the buffer gets allocated: either by the frontend or backend (be_alloc -> buffer allocated by the backend)
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?
in this use-case we map pages provided by the backend (yes, I know this can be a problem from both security POV and that DomU can die holding pages of Dom0 forever: but still it is a configuration option, so user decides if her use-case needs this and takes responsibility for such a decision).
Please see description of the buffering modes in xen_drm_front.h specifically for backend allocated buffers: ******************************************************************************* * 2. Buffers allocated by the backend ******************************************************************************* * * This mode of operation is run-time configured via guest domain configuration * through XenStore entries. * * For systems which do not provide IOMMU support, but having specific * requirements for display buffers it is possible to allocate such buffers * at backend side and share those with the frontend. * For example, if host domain is 1:1 mapped and has DRM/GPU hardware expecting * physically contiguous memory, this allows implementing zero-copying * use-cases.
-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);
+}