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Date: Tue, 23 Jan 2024 06:09:05 +0000
From: Jason-JH Lin (林睿祥) <Jason-JH.Lin@...iatek.com>
To: "maxime@...no.tech" <maxime@...no.tech>, "daniel.vetter@...ll.ch"
	<daniel.vetter@...ll.ch>
CC: "manasi.d.navare@...el.com" <manasi.d.navare@...el.com>,
	"linux-mediatek@...ts.infradead.org" <linux-mediatek@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"michel@...nzer.net" <michel@...nzer.net>, "intel-gfx@...ts.freedesktop.org"
	<intel-gfx@...ts.freedesktop.org>, "chunkuang.hu@...nel.org"
	<chunkuang.hu@...nel.org>, "linux-arm-msm@...r.kernel.org"
	<linux-arm-msm@...r.kernel.org>, "mikita.lipski@....com"
	<mikita.lipski@....com>, "dmitry.baryshkov@...aro.org"
	<dmitry.baryshkov@...aro.org>, "tzimmermann@...e.de" <tzimmermann@...e.de>,
	"daniel.vetter@...el.com" <daniel.vetter@...el.com>,
	"nicholas.kazlauskas@....com" <nicholas.kazlauskas@....com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"quic_abhinavk@...cinc.com" <quic_abhinavk@...cinc.com>,
	Project_Global_Chrome_Upstream_Group
	<Project_Global_Chrome_Upstream_Group@...iatek.com>,
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	<sean@...rly.run>, "matthias.bgg@...il.com" <matthias.bgg@...il.com>,
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	"fshao@...omium.org" <fshao@...omium.org>,
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	<linux-arm-kernel@...ts.infradead.org>, "jani.nikula@...el.com"
	<jani.nikula@...el.com>, "angelogioacchino.delregno@...labora.com"
	<angelogioacchino.delregno@...labora.com>, "freedreno@...ts.freedesktop.org"
	<freedreno@...ts.freedesktop.org>
Subject: Re: [PATCH] drm/atomic-helpers: remove legacy_cursor_update hacks

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?

Regards,
Jason-JH.Lin

On Tue, 2023-03-07 at 15:56 +0100, Maxime Ripard wrote:
> Hi,
> 
> On Thu, Feb 16, 2023 at 12:12:13PM +0100, Daniel Vetter wrote:
> > 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.
> 
> Thanks for submitting that patch. It's been in the downstream RPi
> tree
> for a while, so I'd really like it to be merged eventually :)
> 
> Acked-by: Maxime Ripard <maxime@...no.tech>
> 
> Maxime

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