drm/amdgpu: shadow in shadow_list without tbo.mem.start cause page fault in sriov TDR

shadow was added into shadow_list by amdgpu_bo_create_shadow.
meanwhile, shadow->tbo.mem was not fully configured.
tbo.mem would be fully configured by amdgpu_vm_sdma_map_table until calling amdgpu_vm_clear_bo.
If sriov TDR occurred between amdgpu_bo_create_shadow and amdgpu_vm_sdma_map_table,
amdgpu_device_recover_vram would deal with shadow without tbo.mem.start.

Signed-off-by: Wentao Lou <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

···
 
 		/* No need to recover an evicted BO */
 		if (shadow->tbo.mem.mem_type != TTM_PL_TT ||
+		    shadow->tbo.mem.start == AMDGPU_BO_INVALID_OFFSET ||
 		    shadow->parent->tbo.mem.mem_type != TTM_PL_VRAM)
 			continue;