From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [Xen-devel][PATCH] drm/xen-front: Fix mmap attributes for display buffers Date: Tue, 29 Jan 2019 19:07:41 +0000 Message-ID: References: <20190129150422.19867-1-andr2000@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20190129150422.19867-1-andr2000@gmail.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org 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 List-Id: dri-devel@lists.freedesktop.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