[PATCH] drm/vram-helper: Reuse existing page mappings in vmap

[Thomas Zimmermann]

For performance, BO page mappings can stay in place even if the
map counter has returned to 0. In these cases, the existing page
mapping has to be reused by the next vmap operation. Otherwise
a new mapping would be installed and the old mapping's pages leak.

Fix the issue by reusing existing page mappings for vmap operations.

Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
Fixes: 1086db71a1db ("drm/vram-helper: Remove invariant parameters from internal kmap function")
Acked-by: Christian König <christian.koenig at amd.com>
Tested-by: Eli Cohen <elic at nvidia.com>
Reported-by: Eli Cohen <elic at nvidia.com>
Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
Cc: Christian König <christian.koenig at amd.com>
Cc: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
Cc: Maxime Ripard <mripard at kernel.org>
Cc: David Airlie <airlied at linux.ie>
Cc: Daniel Vetter <daniel at ffwll.ch>
Cc: dri-devel at lists.freedesktop.org
---
 drivers/gpu/drm/drm_gem_vram_helper.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
index 02ca22e90290..0b232a73c1b7 100644
--- a/drivers/gpu/drm/drm_gem_vram_helper.c
+++ b/drivers/gpu/drm/drm_gem_vram_helper.c
@@ -387,9 +387,16 @@ static int drm_gem_vram_kmap_locked(struct drm_gem_vram_object *gbo,
 	if (gbo->vmap_use_count > 0)
 		goto out;
 
-	ret = ttm_bo_vmap(&gbo->bo, &gbo->map);
-	if (ret)
-		return ret;
+	/*
+	 * VRAM helpers unmap the BO only on demand. So the previous
+	 * page mapping might still be around. Only vmap if the there's
+	 * no mapping present.
+	 */
+	if (dma_buf_map_is_null(&gbo->map)) {
+		ret = ttm_bo_vmap(&gbo->bo, &gbo->map);
+		if (ret)
+			return ret;
+	}
 
 out:
 	++gbo->vmap_use_count;
@@ -577,6 +584,7 @@ static void drm_gem_vram_bo_driver_move_notify(struct drm_gem_vram_object *gbo,
 		return;
 
 	ttm_bo_vunmap(bo, &gbo->map);
+	dma_buf_map_clear(&gbo->map); /* explicitly clear mapping for next vmap call */
 }
 
 static int drm_gem_vram_bo_driver_move(struct drm_gem_vram_object *gbo,
-- 
2.29.2