linux-kernel - [Xen-devel][PATCH] drm/xen-front: Fix mmap attributes for display buffers

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Date:   Tue, 29 Jan 2019 17:04:22 +0200
From:   Oleksandr Andrushchenko <andr2000@...il.com>
To:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, daniel.vetter@...el.com,
        jgross@...e.com, boris.ostrovsky@...cle.com, kraxel@...hat.com,
        noralf@...nnes.org, hch@...radead.org, julien.grall@....com
Cc:     andr2000@...il.com,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>
Subject: [Xen-devel][PATCH] drm/xen-front: Fix mmap attributes for display buffers

From: Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>

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 <oleksandr_andrushchenko@...m.com>
Suggested-by: Julien Grall <julien.grall@....com>
---
 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);
 
 	/*
 	 * vm_operations_struct.fault handler will be called if CPU access
@@ -283,7 +282,7 @@ void *xen_drm_front_gem_prime_vmap(struct drm_gem_object *gem_obj)
 		return NULL;
 
 	return vmap(xen_obj->pages, xen_obj->num_pages,
-		    VM_MAP, pgprot_writecombine(PAGE_KERNEL));
+		    VM_MAP, PAGE_KERNEL);
 }
 
 void xen_drm_front_gem_prime_vunmap(struct drm_gem_object *gem_obj,
-- 
2.20.1