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

On Thu, Jan 25, 2024 at 07:17:21PM +0100, Daniel Vetter wrote:

On Tue, Jan 23, 2024 at 06:09:05AM +0000, Jason-JH Lin (林睿祥) wrote:

quoted

Hi Maxime, Daniel,

We encountered similar issue with mediatek SoCs.

We have found that in drm_atomic_helper_commit_rpm(), when disabling
the cursor plane, the old_state->legacy_cursor_update in
drm_atomic_wait_for_vblank() is set to true.
As the result, we are not actually waiting for a vlbank to wait for our
hardware to close the cursor plane. Subsequently, the execution
proceeds to drm_atomic_helper_cleanup_planes() to  free the cursor
buffer. This can lead to use-after-free issues with our hardware.

Could you please apply this patch to fix our problem?
Or are there any considerations for not applying this patch?

Mostly it needs someone to collect a pile of acks/tested-by and then land
it.

I'd be _very_ happy if someone else can take care of that ...

There's also the potential issue that it might slow down some of the
legacy X11 use-cases that really needed a non-blocking cursor, but I think
all the drivers where this matters have switched over to the async plane
update stuff meanwhile. So hopefully that's good.

I think there was also a regression with msm no one really figured out?

Maxime