[PATCH v4] drm/atomic-helpers: remove legacy_cursor_update hacks

[Ville Syrjälä]

On Thu, Mar 31, 2022 at 03:05:45PM +0200, Maxime Ripard wrote:
> From: Daniel Vetter <daniel.vetter at ffwll.ch>
> 
> The stuff never really worked, and leads to lots of fun because it
> out-of-order frees atomic states. Which upsets KASAN, among other
> things.
> 
> For async updates we now have a more solid solution with the
> ->atomic_async_check and ->atomic_async_commit hooks. Support for that
> for msm and vc4 landed. nouveau and i915 have their own commit
> routines, doing something similar.
> 
> For everyone else it's probably better to remove the use-after-free
> bug, and encourage folks to use the async support instead. The
> affected drivers which register a legacy cursor plane and don't either
> use the new async stuff or their own commit routine are: amdgpu,
> atmel, mediatek, qxl, rockchip, sti, sun4i, tegra, virtio, and vmwgfx.
> 
> Inspired by an amdgpu bug report.
> 
> v2: Drop RFC, I think with amdgpu converted over to use
> atomic_async_check/commit done in
> 
> commit 674e78acae0dfb4beb56132e41cbae5b60f7d662
> Author: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
> Date:   Wed Dec 5 14:59:07 2018 -0500
> 
>     drm/amd/display: Add fast path for cursor plane updates
> 
> we don't have any driver anymore where we have userspace expecting
> solid legacy cursor support _and_ they are using the atomic helpers in
> their fully glory. So we can retire this.
> 
> v3: Paper over msm and i915 regression. The complete_all is the only
> thing missing afaict.
> 
> v4: Rebased on recent kernel, added extra link for vc4 bug.
> 
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=199425
> Link: https://lore.kernel.org/all/20220221134155.125447-9-maxime@cerno.tech/
> Cc: mikita.lipski at amd.com
> Cc: Michel Dänzer <michel at daenzer.net>
> Cc: harry.wentland at amd.com
> Cc: Rob Clark <robdclark at gmail.com>
> Cc: "Kazlauskas, Nicholas" <nicholas.kazlauskas at amd.com>
> Tested-by: Maxime Ripard <maxime at cerno.tech>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Signed-off-by: Maxime Ripard <maxime at cerno.tech>
> ---
>  drivers/gpu/drm/drm_atomic_helper.c          | 13 -------------
>  drivers/gpu/drm/i915/display/intel_display.c | 13 +++++++++++++
>  drivers/gpu/drm/msm/msm_atomic.c             |  2 ++
>  3 files changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
> index 9603193d2fa1..a2899af82b4a 100644
> --- a/drivers/gpu/drm/drm_atomic_helper.c
> +++ b/drivers/gpu/drm/drm_atomic_helper.c
> @@ -1498,13 +1498,6 @@ drm_atomic_helper_wait_for_vblanks(struct drm_device *dev,
>  	int i, ret;
>  	unsigned int crtc_mask = 0;
>  
> -	 /*
> -	  * Legacy cursor ioctls are completely unsynced, and userspace
> -	  * relies on that (by doing tons of cursor updates).
> -	  */
> -	if (old_state->legacy_cursor_update)
> -		return;
> -
>  	for_each_oldnew_crtc_in_state(old_state, crtc, old_crtc_state, new_crtc_state, i) {
>  		if (!new_crtc_state->active)
>  			continue;
> @@ -2135,12 +2128,6 @@ int drm_atomic_helper_setup_commit(struct drm_atomic_state *state,
>  			continue;
>  		}
>  
> -		/* Legacy cursor updates are fully unsynced. */
> -		if (state->legacy_cursor_update) {
> -			complete_all(&commit->flip_done);
> -			continue;
> -		}
> -
>  		if (!new_crtc_state->event) {
>  			commit->event = kzalloc(sizeof(*commit->event),
>  						GFP_KERNEL);
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index bf7ce684dd8e..bde32f5a33cb 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -8855,6 +8855,19 @@ static int intel_atomic_commit(struct drm_device *dev,
>  				state->base.legacy_cursor_update = false;
>  	}
>  
> +	/*
> +	 * FIXME: Cut over to (async) commit helpers instead of hand-rolling
> +	 * everything.
> +	 */

Intel cursors can't even do async updates so this is rather
nonsensical. What we need is some kind of reasonable mailbox
support.

> +	if (state->base.legacy_cursor_update) {
> +		struct intel_crtc_state *new_crtc_state;
> +		struct intel_crtc *crtc;
> +		int i;
> +
> +		for_each_new_intel_crtc_in_state(state, crtc, new_crtc_state, i)
> +			complete_all(&new_crtc_state->uapi.commit->flip_done);
> +	}

You can complete what doesn't yet exist. Missing cc: intel-gfx for fireworks.

> +
>  	ret = intel_atomic_prepare_commit(state);
>  	if (ret) {
>  		drm_dbg_atomic(&dev_priv->drm,
> diff --git a/drivers/gpu/drm/msm/msm_atomic.c b/drivers/gpu/drm/msm/msm_atomic.c
> index 27c9ae563f2f..6ed14fafa40c 100644
> --- a/drivers/gpu/drm/msm/msm_atomic.c
> +++ b/drivers/gpu/drm/msm/msm_atomic.c
> @@ -237,6 +237,8 @@ void msm_atomic_commit_tail(struct drm_atomic_state *state)
>  		/* async updates are limited to single-crtc updates: */
>  		WARN_ON(crtc_mask != drm_crtc_mask(async_crtc));
>  
> +		complete_all(&async_crtc->state->commit->flip_done);
> +
>  		/*
>  		 * Start timer if we don't already have an update pending
>  		 * on this crtc:
> -- 
> 2.35.1

-- 
Ville Syrjälä
Intel