From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id CAF10C169C4 for ; Tue, 29 Jan 2019 19:07:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A813D20869 for ; Tue, 29 Jan 2019 19:07:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729298AbfA2THq (ORCPT ); Tue, 29 Jan 2019 14:07:46 -0500 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:43006 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726984AbfA2THp (ORCPT ); Tue, 29 Jan 2019 14:07:45 -0500 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4BE87A78; Tue, 29 Jan 2019 11:07:45 -0800 (PST) Received: from [10.1.35.17] (e110479-lin.cambridge.arm.com [10.1.35.17]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C2C883F557; Tue, 29 Jan 2019 11:07:42 -0800 (PST) Subject: Re: [Xen-devel][PATCH] drm/xen-front: Fix mmap attributes for display buffers To: Oleksandr Andrushchenko , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, daniel.vetter@intel.com, jgross@suse.com, boris.ostrovsky@oracle.com, kraxel@redhat.com, noralf@tronnes.org, hch@infradead.org Cc: Oleksandr Andrushchenko References: <20190129150422.19867-1-andr2000@gmail.com> From: Julien Grall Message-ID: Date: Tue, 29 Jan 2019 19:07:41 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190129150422.19867-1-andr2000@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Oleksandr, On 1/29/19 3:04 PM, Oleksandr Andrushchenko wrote: > From: Oleksandr Andrushchenko > > When GEM backing storage is allocated those are normal pages, > so there is no point using pgprot_writecombine while mmaping. > This fixes mismatch of buffer pages' memory attributes between > the frontend and backend which may cause screen artifacts. > > Fixes: c575b7eeb89f ("drm/xen-front: Add support for Xen PV display frontend") > > Signed-off-by: Oleksandr Andrushchenko > Suggested-by: Julien Grall > --- > drivers/gpu/drm/xen/xen_drm_front_gem.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/xen/xen_drm_front_gem.c b/drivers/gpu/drm/xen/xen_drm_front_gem.c > index d303a2e17f5e..9d5c03d7668d 100644 > --- a/drivers/gpu/drm/xen/xen_drm_front_gem.c > +++ b/drivers/gpu/drm/xen/xen_drm_front_gem.c > @@ -235,8 +235,7 @@ static int gem_mmap_obj(struct xen_gem_object *xen_obj, > vma->vm_flags &= ~VM_PFNMAP; > vma->vm_flags |= VM_MIXEDMAP; > vma->vm_pgoff = 0; > - vma->vm_page_prot = > - pgprot_writecombine(vm_get_page_prot(vma->vm_flags)); > + vma->vm_page_prot = vm_get_page_prot(vma->vm_flags); The patch looks good to me. It would be worth expanding the comment a bit before to explain that we overwrite vm_page_prot to use cacheable attribute as required by the Xen ABI. With the comment updated: Acked-by: Julien Grall Cheers, -- Julien Grall