On Wed, Jan 31, 2024 at 12:26:45PM +0200, Dmitry Baryshkov wrote: > On Wed, 31 Jan 2024 at 11:11, Daniel Vetter <dan...@ffwll.ch> wrote: > > > > On Wed, Jan 31, 2024 at 05:17:08AM +0000, Jason-JH Lin (林睿祥) wrote: > > > On Thu, 2024-01-25 at 19:17 +0100, Daniel Vetter wrote: > > > > > > > > External email : Please do not click links or open attachments until > > > > you have verified the sender or the content. > > > > On Tue, Jan 23, 2024 at 06:09:05AM +0000, Jason-JH Lin (林睿祥) wrote: > > > > > 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. > > > > > > > > > > Got it. I would add tested-by tag for mediatek SoC. > > > > > > > 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 all the drivers should have switched to async plane update. > > > > > > Can we add the checking condition to see if atomic_async_update/check > > > function are implemented? > > > > Pretty sure not all have done that, so really it boils down to whether we > > break a real user's use-case. Which pretty much can only be checked by > > merging the patch (hence the requirement to get as many acks as possible > > from display drivers) and then being willing to handle any fallout that's > > reported as regressions for a specific driver. > > > > It's a pile of work, at least when it goes south, that's why I'm looking > > for volunteers. > > I can check this on all sensible msm generations, including mdp4, but > it will be next week, after the FOSDEM. > > BTW, for technical reasons one of the msm platforms still has the > legacy cursor implementation might it be related?
Yeah, msm is one of the drivers I had to change with some hacks to avoid really bad fallout. It should still work like before, but that's one that definitely needs testing. -Sima > > > > > Note that handling the fallout doesn't mean you have to fix that specific > > driver, the only realistic option might be to reinstate the legacy cursor > > behaviour, but as an explicit opt-in that only that specific driver > > enables. > > > > So maybe for next round of that patch it might be good to have a 2nd patch > > which implements this fallback plan in the shared atomic modeset code? > > > > Cheers, Sima > > > -- > With best wishes > Dmitry -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
