drm/amd/display: Do not skip unrelated mode changes in DSC validation

Starting with commit 17ce8a6907f7 ("drm/amd/display: Add dsc pre-validation in
atomic check"), amdgpu resets the CRTC state mode_changed flag to false when
recomputing the DSC configuration results in no timing change for a particular
stream.

However, this is incorrect in scenarios where a change in MST/DSC configuration
happens in the same KMS commit as another (unrelated) mode change. For example,
the integrated panel of a laptop may be configured differently (e.g., HDR
enabled/disabled) depending on whether external screens are attached. In this
case, plugging in external DP-MST screens may result in the mode_changed flag
being dropped incorrectly for the integrated panel if its DSC configuration
did not change during precomputation in pre_validate_dsc().

At this point, however, dm_update_crtc_state() has already created new streams
for CRTCs with DSC-independent mode changes. In turn,
amdgpu_dm_commit_streams() will never release the old stream, resulting in a
memory leak. amdgpu_dm_atomic_commit_tail() will never acquire a reference to
the new stream either, which manifests as a use-after-free when the stream gets
disabled later on:

BUG: KASAN: use-after-free in dc_stream_release+0x25/0x90 [amdgpu]
Write of size 4 at addr ffff88813d836524 by task kworker/9:9/29977

Workqueue: events drm_mode_rmfb_work_fn
Call Trace:
 <TASK>
 dump_stack_lvl+0x6e/0xa0
 print_address_description.constprop.0+0x88/0x320
 ? dc_stream_release+0x25/0x90 [amdgpu]
 print_report+0xfc/0x1ff
 ? srso_alias_return_thunk+0x5/0xfbef5
 ? __virt_addr_valid+0x225/0x4e0
 ? dc_stream_release+0x25/0x90 [amdgpu]
 kasan_report+0xe1/0x180
 ? dc_stream_release+0x25/0x90 [amdgpu]
 kasan_check_range+0x125/0x200
 dc_stream_release+0x25/0x90 [amdgpu]
 dc_state_destruct+0x14d/0x5c0 [amdgpu]
 dc_state_release.part.0+0x4e/0x130 [amdgpu]
 dm_atomic_destroy_state+0x3f/0x70 [amdgpu]
 drm_atomic_state_default_clear+0x8ee/0xf30
 ? drm_mode_object_put.part.0+0xb1/0x130
 __drm_atomic_state_free+0x15c/0x2d0
 atomic_remove_fb+0x67e/0x980

Since there is no reliable way of figuring out whether a CRTC has unrelated
mode changes pending at the time of DSC validation, remember the value of the
mode_changed flag from before the point where a CRTC was marked as potentially
affected by a change in DSC configuration. Reset the mode_changed flag to this
earlier value instead in pre_validate_dsc().

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/5004
Fixes: 17ce8a6907f7 ("drm/amd/display: Add dsc pre-validation in atomic check")
Signed-off-by: Yussuf Khalil <dev@pp3345.net>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit cc7c7121ae082b7b82891baa7280f1ff2608f22b)

3 files changed, 9 insertions, 1 deletions

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 085cc98bd875..a9c398b1516b 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -12524,6 +12524,11 @@ static int amdgpu_dm_atomic_check(struct drm_device *dev,
 
 	if (dc_resource_is_dsc_encoding_supported(dc)) {
 		for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
+			dm_new_crtc_state = to_dm_crtc_state(new_crtc_state);
+			dm_new_crtc_state->mode_changed_independent_from_dsc = new_crtc_state->mode_changed;
+		}
+
+		for_each_oldnew_crtc_in_state(state, crtc, old_crtc_state, new_crtc_state, i) {
 			if (drm_atomic_crtc_needs_modeset(new_crtc_state)) {
 				ret = add_affected_mst_dsc_crtcs(state, crtc);
 				if (ret) {
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
index 800813671748..d15812d51d72 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
@@ -984,6 +984,7 @@ struct dm_crtc_state {
 
 	bool freesync_vrr_info_changed;
 
+	bool mode_changed_independent_from_dsc;
 	bool dsc_force_changed;
 	bool vrr_supported;
 	struct mod_freesync_config freesync_config;
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
index 7be50e8c0636..5d8c4c7020b1 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_mst_types.c
@@ -1744,9 +1744,11 @@ int pre_validate_dsc(struct drm_atomic_state *state,
 			int ind = find_crtc_index_in_state_by_stream(state, stream);
 
 			if (ind >= 0) {
+				struct dm_crtc_state *dm_new_crtc_state = to_dm_crtc_state(state->crtcs[ind].new_state);
+
 				DRM_INFO_ONCE("%s:%d MST_DSC no mode changed for stream 0x%p\n",
 						__func__, __LINE__, stream);
-				state->crtcs[ind].new_state->mode_changed = 0;
+				dm_new_crtc_state->base.mode_changed = dm_new_crtc_state->mode_changed_independent_from_dsc;
 			}
 		}
 	}