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

["Kazlauskas, Nicholas" <nicholas.kazlauskas@amd.com>]

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.

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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> 

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