Re: [PATCH 3/7] drm/amd/display: Avoid using unvalidated tiling_flags and tmz_surface in prepare_planes

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Aug 10, 2020 at 02:30:05PM +0200, Christian König wrote:
> Am 10.08.20 um 14:25 schrieb Daniel Vetter:
> > On Fri, Aug 07, 2020 at 10:29:09AM -0400, Kazlauskas, Nicholas wrote:
> > > On 2020-08-07 4:30 a.m., daniel@ffwll.ch wrote:
> > > > On Thu, Jul 30, 2020 at 04:36:38PM -0400, Nicholas Kazlauskas wrote:
> > > > > [Why]
> > > > > We're racing with userspace as the flags could potentially change
> > > > > from when we acquired and validated them in commit_check.
> > > > Uh ... I didn't know these could change. I think my comments on Bas'
> > > > series are even more relevant now. I think long term would be best to bake
> > > > these flags in at addfb time when modifiers aren't set. And otherwise
> > > > always use the modifiers flag, and completely ignore the legacy flags
> > > > here.
> > > > -Daniel
> > > > 
> > > There's a set tiling/mod flags IOCTL that can be called after addfb happens,
> > > so unless there's some sort of driver magic preventing this from working
> > > when it's already been pinned for scanout then I don't see anything stopping
> > > this from happening.
> > > 
> > > I still need to review the modifiers series in a little more detail but that
> > > looks like a good approach to fixing these kind of issues.
> > Yeah we had the same model for i915, but it's awkward and can surprise
> > compositors (since the client could change the tiling mode from underneath
> > the compositor). So freezing the tiling mode at addfb time is the right
> > thing to do, and anyway how things work with modifiers.
> > 
> > Ofc maybe good to audit the -amd driver, but hopefully it doesn't do
> > anything silly with changed tiling. If it does, it's kinda sad day.
> 
> Marek should know this right away, but I think we only set the tilling flags
> once while exporting the BO and then never change them.

Yeah it's the only reasonable model really, since set/get_tiling is not
synchronized with any winsys protocol. So full of races by design.

The only thing I'd worry about is if you do set_tiling after addfb in your
ddx. That one is save, but would badly break if we sample modifiers from
set_tiling flags only once at addfb time.
-Daniel

> 
> Regards,
> Christian.
> 
> > 
> > Btw for i915 we even went a step further, and made the set_tiling ioctl
> > return an error if a framebuffer for that gem_bo existed. Just to make
> > sure we don't ever accidentally break this.
> > 
> > Cheers, Daniel
> > 
> > > Regards,
> > > Nicholas Kazlauskas
> > > 
> > > > > [How]
> > > > > We unfortunately can't drop this function in its entirety from
> > > > > prepare_planes since we don't know the afb->address at commit_check
> > > > > time yet.
> > > > > 
> > > > > So instead of querying new tiling_flags and tmz_surface use the ones
> > > > > from the plane_state directly.
> > > > > 
> > > > > While we're at it, also update the force_disable_dcc option based
> > > > > on the state from atomic check.
> > > > > 
> > > > > Cc: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
> > > > > Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
> > > > > Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
> > > > > ---
> > > > >    .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 36 ++++++++++---------
> > > > >    1 file changed, 19 insertions(+), 17 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > > > > index bf1881bd492c..f78c09c9585e 100644
> > > > > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > > > > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > > > > @@ -5794,14 +5794,8 @@ static int dm_plane_helper_prepare_fb(struct drm_plane *plane,
> > > > >    	struct list_head list;
> > > > >    	struct ttm_validate_buffer tv;
> > > > >    	struct ww_acquire_ctx ticket;
> > > > > -	uint64_t tiling_flags;
> > > > >    	uint32_t domain;
> > > > >    	int r;
> > > > > -	bool tmz_surface = false;
> > > > > -	bool force_disable_dcc = false;
> > > > > -
> > > > > -	dm_plane_state_old = to_dm_plane_state(plane->state);
> > > > > -	dm_plane_state_new = to_dm_plane_state(new_state);
> > > > >    	if (!new_state->fb) {
> > > > >    		DRM_DEBUG_DRIVER("No FB bound\n");
> > > > > @@ -5845,27 +5839,35 @@ static int dm_plane_helper_prepare_fb(struct drm_plane *plane,
> > > > >    		return r;
> > > > >    	}
> > > > > -	amdgpu_bo_get_tiling_flags(rbo, &tiling_flags);
> > > > > -
> > > > > -	tmz_surface = amdgpu_bo_encrypted(rbo);
> > > > > -
> > > > >    	ttm_eu_backoff_reservation(&ticket, &list);
> > > > >    	afb->address = amdgpu_bo_gpu_offset(rbo);
> > > > >    	amdgpu_bo_ref(rbo);
> > > > > +	/**
> > > > > +	 * We don't do surface updates on planes that have been newly created,
> > > > > +	 * but we also don't have the afb->address during atomic check.
> > > > > +	 *
> > > > > +	 * Fill in buffer attributes depending on the address here, but only on
> > > > > +	 * newly created planes since they're not being used by DC yet and this
> > > > > +	 * won't modify global state.
> > > > > +	 */
> > > > > +	dm_plane_state_old = to_dm_plane_state(plane->state);
> > > > > +	dm_plane_state_new = to_dm_plane_state(new_state);
> > > > > +
> > > > >    	if (dm_plane_state_new->dc_state &&
> > > > > -			dm_plane_state_old->dc_state != dm_plane_state_new->dc_state) {
> > > > > -		struct dc_plane_state *plane_state = dm_plane_state_new->dc_state;
> > > > > +	    dm_plane_state_old->dc_state != dm_plane_state_new->dc_state) {
> > > > > +		struct dc_plane_state *plane_state =
> > > > > +			dm_plane_state_new->dc_state;
> > > > > +		bool force_disable_dcc = !plane_state->dcc.enable;
> > > > > -		force_disable_dcc = adev->asic_type == CHIP_RAVEN && adev->in_suspend;
> > > > >    		fill_plane_buffer_attributes(
> > > > >    			adev, afb, plane_state->format, plane_state->rotation,
> > > > > -			tiling_flags, &plane_state->tiling_info,
> > > > > -			&plane_state->plane_size, &plane_state->dcc,
> > > > > -			&plane_state->address, tmz_surface,
> > > > > -			force_disable_dcc);
> > > > > +			dm_plane_state_new->tiling_flags,
> > > > > +			&plane_state->tiling_info, &plane_state->plane_size,
> > > > > +			&plane_state->dcc, &plane_state->address,
> > > > > +			dm_plane_state_new->tmz_surface, force_disable_dcc);
> > > > >    	}
> > > > >    	return 0;
> > > > > -- 
> > > > > 2.25.1
> > > > > 
> > > > > _______________________________________________
> > > > > dri-devel mailing list
> > > > > dri-devel@lists.freedesktop.org
> > > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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