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

Thu Mar 31 19:52:54 UTC 2022

On Thu, Mar 31, 2022 at 09:11:29PM +0200, Daniel Vetter wrote:
> On Thu, Mar 31, 2022 at 06:48:43PM +0300, Ville Syrjälä wrote:
> > On Thu, Mar 31, 2022 at 05:14:29PM +0200, Daniel Vetter wrote:
> > > On Thu, Mar 31, 2022 at 04:25:13PM +0300, Ville Syrjälä wrote:
> > > > 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.
> > > 
> > > This is not the async plane update you're thinking of. i915 really should
> > > switch over more to atomic helpers.
> > 
> > The comment should be clarified then. As is I have no real idea
> > what it's trying to say.
> 
> Use drm_atomic_commit and only overwrite atomic_commit_tail.

You mean drm_atomic_helper_commit() I suppose?

> But I'm not
> really clear why the comment isn't clear - i915 is the only driver not
> using them, maybe should start to take a look when they're so unfamiliar
> :-P

There are a lot of problems with that:
- no uapi/hw state split so if there's anything that looks
  at the state it's very likely going to get things wrong
- it doesn't know anything about i915's own state objects
- uses wrong workqueues

Those are the ones that immediately came to mind when I looked
at it. Probably I missed some others as well.

-- 
Ville Syrjälä
Intel