From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751447AbeBWOfz (ORCPT ); Fri, 23 Feb 2018 09:35:55 -0500 Received: from userp2130.oracle.com ([156.151.31.86]:57448 "EHLO userp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751314AbeBWOfy (ORCPT ); Fri, 23 Feb 2018 09:35:54 -0500 Subject: Re: [PATCH 5/9] drm/xen-front: Implement handling of shared display buffers To: Oleksandr Andrushchenko , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, airlied@linux.ie, daniel.vetter@intel.com, seanpaul@chromium.org, gustavo@padovan.org, jgross@suse.com, konrad.wilk@oracle.com Cc: Oleksandr Andrushchenko References: <1519200222-20623-1-git-send-email-andr2000@gmail.com> <1519200222-20623-6-git-send-email-andr2000@gmail.com> <11ce6c96-1739-435c-4b6f-c9f5d02a2905@oracle.com> From: Boris Ostrovsky Message-ID: <36003bb4-6fc9-f8f9-2817-103bf0f543e9@oracle.com> Date: Fri, 23 Feb 2018 09:36:16 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=8812 signatures=668677 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=710 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1711220000 definitions=main-1802230182 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/23/2018 02:53 AM, Oleksandr Andrushchenko wrote: > On 02/23/2018 02:25 AM, Boris Ostrovsky wrote: >> On 02/21/2018 03:03 AM, Oleksandr Andrushchenko wrote: >>> static int __init xen_drv_init(void) >>> { >>> + /* At the moment we only support case with XEN_PAGE_SIZE == >>> PAGE_SIZE */ >>> + BUILD_BUG_ON(XEN_PAGE_SIZE != PAGE_SIZE); >> >> Why BUILD_BUG_ON? This should simply not load if page sizes are >> different. >> >> > This is a compile time check, so if kernel/Xen is configured > to use page size combination which is not supported by the > driver it will fail during compilation. This seems correct to me, > because you shouldn't even try to load the driver which > cannot handle different page sizes to not make any harm. This will prevent whole kernel from building. So, for example, randconfig builds will fail. >> >> >> >>> + ret = gnttab_map_refs(map_ops, NULL, buf->pages, buf->num_pages); >>> + BUG_ON(ret); >> >> We should try not to BUG*(). There are a few in this patch (and possibly >> others) that I think can be avoided. >> > I will rework BUG_* for map/unmap code to handle errors, > but will still leave > /* either pages or sgt, not both */ > BUG_ON(cfg->pages && cfg->sgt); > which is a real driver bug and must not happen Why not return an error? In fact, AFAICS you only call it in patch 9 where both of these can be tested, in which case something like -EINVAL would look reasonable. -boris