From d3d9ef6e9f295658bb330d8716d64d4549b9e7f1 Mon Sep 17 00:00:00 2001 From: Nicholas Kazlauskas Date: Fri, 14 Dec 2018 12:26:58 -0500 Subject: [PATCH 0954/2940] drm/amd/display: Skip fast cursor updates for fb changes [Why] The behavior of drm_atomic_helper_cleanup_planes differs depending on whether the commit was asynchronous or not. When it's called from amdgpu_dm_atomic_commit_tail during a typical atomic commit the plane state has been swapped so it calls cleanup_fb on the old plane state. However, in the asynchronous commit codepath the call to drm_atomic_helper_commit also calls dm_plane_helper_cleanup_fb after atomic_async_update has been called. Since the plane state is updated in place and has not been swapped the cleanup_fb call affects the new plane state. This results in a use after free for the given sequence: - Fast update, fb1 pin/ref, fb1 unpin/unref - Fast update, fb2 pin/ref, fb2 unpin/unref - Slow update, fb1 pin/ref, fb2 unpin/unref - Fast update, fb2 pin/ref -> use after free. bug [How] Disallow framebuffer changes in the fast path. Since this includes a NULL framebuffer, this means that only framebuffers that have been previously pin+ref at least once will be used, preventing a use after free. This has a significant throughput reduction for cursor updates where the framebuffer changes. For most desktop usage this isn't a problem, but it does introduce performance regressions for two specific IGT tests: - cursor-vs-flip-toggle - cursor-vs-flip-varying-size Fixes: 2cc751931afc ("drm/amd/display: Add fast path for cursor plane updates") Signed-off-by: Nicholas Kazlauskas Reviewed-by: Andrey Grodzovsky Reviewed-by: Harry Wentland Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c index 6f6d11d98f37..61067d206caf 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -3658,10 +3658,20 @@ static int dm_plane_atomic_check(struct drm_plane *plane, static int dm_plane_atomic_async_check(struct drm_plane *plane, struct drm_plane_state *new_plane_state) { + struct drm_plane_state *old_plane_state = + drm_atomic_get_old_plane_state(new_plane_state->state, plane); + /* Only support async updates on cursor planes. */ if (plane->type != DRM_PLANE_TYPE_CURSOR) return -EINVAL; + /* + * DRM calls prepare_fb and cleanup_fb on new_plane_state for + * async commits so don't allow fb changes. + */ + if (old_plane_state->fb != new_plane_state->fb) + return -EINVAL; + return 0; } -- 2.17.1