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

["Christian König" <ckoenig.leichtzumerken@gmail.com>]

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.

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
>>>>
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