drm/vc4: kms: Wait on previous FIFO users before a commit

If we're having two subsequent, non-blocking, commits on two different
CRTCs that share no resources, there's no guarantee on the order of
execution of both commits.

However, the second one will consider the first one as the old state,
and will be in charge of freeing it once that second commit is done.

If the first commit happens after that second commit, it might access
some resources related to its state that has been freed, resulting in a
use-after-free bug.

The standard DRM objects are protected against this, but our HVS private
state isn't so let's make sure we wait for all the previous FIFO users
to finish their commit before going with our own.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201204151138.1739736-5-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_kms.c

@@ -40,6 +40,11 @@ static struct vc4_ctm_state *to_vc4_ctm_state(struct drm_private_state *priv)
 struct vc4_hvs_state {
 	struct drm_private_state base;
 	unsigned int unassigned_channels;
+
+	struct {
+		unsigned in_use: 1;
+		struct drm_crtc_commit *pending_commit;
+	} fifo_state[HVS_NUM_CHANNELS];
 };
 
 static struct vc4_hvs_state *
@@ -182,6 +187,32 @@ vc4_ctm_commit(struct vc4_dev *vc4, struct drm_atomic_state *state)
 		  VC4_SET_FIELD(ctm_state->fifo, SCALER_OLEDOFFS_DISPFIFO));
 }
 
+static struct vc4_hvs_state *
+vc4_hvs_get_new_global_state(struct drm_atomic_state *state)
+{
+	struct vc4_dev *vc4 = to_vc4_dev(state->dev);
+	struct drm_private_state *priv_state;
+
+	priv_state = drm_atomic_get_new_private_obj_state(state, &vc4->hvs_channels);
+	if (IS_ERR(priv_state))
+		return ERR_CAST(priv_state);
+
+	return to_vc4_hvs_state(priv_state);
+}
+
+static struct vc4_hvs_state *
+vc4_hvs_get_old_global_state(struct drm_atomic_state *state)
+{
+	struct vc4_dev *vc4 = to_vc4_dev(state->dev);
+	struct drm_private_state *priv_state;
+
+	priv_state = drm_atomic_get_old_private_obj_state(state, &vc4->hvs_channels);
+	if (IS_ERR(priv_state))
+		return ERR_CAST(priv_state);
+
+	return to_vc4_hvs_state(priv_state);
+}
+
 static struct vc4_hvs_state *
 vc4_hvs_get_global_state(struct drm_atomic_state *state)
 {
@@ -308,8 +339,10 @@ vc4_atomic_complete_commit(struct drm_atomic_state *state)
 	struct drm_device *dev = state->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	struct vc4_hvs *hvs = vc4->hvs;
+	struct drm_crtc_state *old_crtc_state;
 	struct drm_crtc_state *new_crtc_state;
 	struct drm_crtc *crtc;
+	struct vc4_hvs_state *old_hvs_state;
 	int i;
 
 	for_each_new_crtc_in_state(state, crtc, new_crtc_state, i) {
@@ -329,6 +362,36 @@ vc4_atomic_complete_commit(struct drm_atomic_state *state)
 
 	drm_atomic_helper_wait_for_dependencies(state);
 
+	old_hvs_state = vc4_hvs_get_old_global_state(state);
+	if (!old_hvs_state)
+		return;
+
+	for_each_old_crtc_in_state(state, crtc, old_crtc_state, i) {
+		struct vc4_crtc_state *vc4_crtc_state =
+			to_vc4_crtc_state(old_crtc_state);
+		struct drm_crtc_commit *commit;
+		unsigned int channel = vc4_crtc_state->assigned_channel;
+		unsigned long done;
+
+		if (channel == VC4_HVS_CHANNEL_DISABLED)
+			continue;
+
+		if (!old_hvs_state->fifo_state[channel].in_use)
+			continue;
+
+		commit = old_hvs_state->fifo_state[i].pending_commit;
+		if (!commit)
+			continue;
+
+		done = wait_for_completion_timeout(&commit->hw_done, 10 * HZ);
+		if (!done)
+			drm_err(dev, "Timed out waiting for hw_done\n");
+
+		done = wait_for_completion_timeout(&commit->flip_done, 10 * HZ);
+		if (!done)
+			drm_err(dev, "Timed out waiting for flip_done\n");
+	}
+
 	drm_atomic_helper_commit_modeset_disables(dev, state);
 
 	vc4_ctm_commit(vc4, state);
@@ -368,6 +431,36 @@ static void commit_work(struct work_struct *work)
 	vc4_atomic_complete_commit(state);
 }
 
+static int vc4_atomic_commit_setup(struct drm_atomic_state *state)
+{
+	struct drm_crtc_state *crtc_state;
+	struct vc4_hvs_state *hvs_state;
+	struct drm_crtc *crtc;
+	unsigned int i;
+
+	hvs_state = vc4_hvs_get_new_global_state(state);
+	if (!hvs_state)
+		return -EINVAL;
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		struct vc4_crtc_state *vc4_crtc_state =
+			to_vc4_crtc_state(crtc_state);
+		unsigned int channel =
+			vc4_crtc_state->assigned_channel;
+
+		if (channel == VC4_HVS_CHANNEL_DISABLED)
+			continue;
+
+		if (!hvs_state->fifo_state[channel].in_use)
+			continue;
+
+		hvs_state->fifo_state[channel].pending_commit =
+			drm_crtc_commit_get(crtc_state->commit);
+	}
+
+	return 0;
+}
+
 /**
  * vc4_atomic_commit - commit validated state object
  * @dev: DRM device
@@ -697,6 +790,7 @@ vc4_hvs_channels_duplicate_state(struct drm_private_obj *obj)
 {
 	struct vc4_hvs_state *old_state = to_vc4_hvs_state(obj->state);
 	struct vc4_hvs_state *state;
+	unsigned int i;
 
 	state = kzalloc(sizeof(*state), GFP_KERNEL);
 	if (!state)
@@ -706,6 +800,16 @@ vc4_hvs_channels_duplicate_state(struct drm_private_obj *obj)
 
 	state->unassigned_channels = old_state->unassigned_channels;
 
+	for (i = 0; i < HVS_NUM_CHANNELS; i++) {
+		state->fifo_state[i].in_use = old_state->fifo_state[i].in_use;
+
+		if (!old_state->fifo_state[i].pending_commit)
+			continue;
+
+		state->fifo_state[i].pending_commit =
+			drm_crtc_commit_get(old_state->fifo_state[i].pending_commit);
+	}
+
 	return &state->base;
 }
 
@@ -713,6 +817,14 @@ static void vc4_hvs_channels_destroy_state(struct drm_private_obj *obj,
 					   struct drm_private_state *state)
 {
 	struct vc4_hvs_state *hvs_state = to_vc4_hvs_state(state);
+	unsigned int i;
+
+	for (i = 0; i < HVS_NUM_CHANNELS; i++) {
+		if (!hvs_state->fifo_state[i].pending_commit)
+			continue;
+
+		drm_crtc_commit_put(hvs_state->fifo_state[i].pending_commit);
+	}
 
 	kfree(hvs_state);
 }
@@ -805,7 +917,10 @@ static int vc4_pv_muxing_atomic_check(struct drm_device *dev,
 
 		/* If we're disabling our CRTC, we put back our channel */
 		if (!new_crtc_state->enable) {
-			hvs_new_state->unassigned_channels |= BIT(old_vc4_crtc_state->assigned_channel);
+			channel = old_vc4_crtc_state->assigned_channel;
+
+			hvs_new_state->unassigned_channels |= BIT(channel);
+			hvs_new_state->fifo_state[channel].in_use = false;
 			new_vc4_crtc_state->assigned_channel = VC4_HVS_CHANNEL_DISABLED;
 			continue;
 		}
@@ -841,6 +956,7 @@ static int vc4_pv_muxing_atomic_check(struct drm_device *dev,
 		channel = ffs(matching_channels) - 1;
 		new_vc4_crtc_state->assigned_channel = channel;
 		hvs_new_state->unassigned_channels &= ~BIT(channel);
+		hvs_new_state->fifo_state[channel].in_use = true;
 	}
 
 	return 0;
@@ -866,6 +982,10 @@ vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 	return vc4_load_tracker_atomic_check(state);
 }
 
+static struct drm_mode_config_helper_funcs vc4_mode_config_helpers = {
+	.atomic_commit_setup	= vc4_atomic_commit_setup,
+};
+
 static const struct drm_mode_config_funcs vc4_mode_funcs = {
 	.atomic_check = vc4_atomic_check,
 	.atomic_commit = vc4_atomic_commit,
@@ -909,6 +1029,7 @@ int vc4_kms_load(struct drm_device *dev)
 	}
 
 	dev->mode_config.funcs = &vc4_mode_funcs;
+	dev->mode_config.helper_private = &vc4_mode_config_helpers;
 	dev->mode_config.preferred_depth = 24;
 	dev->mode_config.async_page_flip = true;
 	dev->mode_config.allow_fb_modifiers = true;