drm/amdkfd: Update get_wave_state() for GFX10

Given control stack is now in the userspace context save restore area
on GFX10, the same as GFX8, it is not needed to copy it back to userspace.
Signed-off-by: Yong Zhao <Yong.Zhao@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdkfd/kfd_mqd_manager_v10.c

@@ -251,18 +251,22 @@ static int get_wave_state(struct mqd_manager *mm, void *mqd,
 {
 	struct v10_compute_mqd *m;
 
-	/* Control stack is located one page after MQD. */
-	void *mqd_ctl_stack = (void *)((uintptr_t)mqd + PAGE_SIZE);
-
 	m = get_mqd(mqd);
 
+	/* Control stack is written backwards, while workgroup context data
+	 * is written forwards. Both starts from m->cp_hqd_cntl_stack_size.
+	 * Current position is at m->cp_hqd_cntl_stack_offset and
+	 * m->cp_hqd_wg_state_offset, respectively.
+	 */
 	*ctl_stack_used_size = m->cp_hqd_cntl_stack_size -
 		m->cp_hqd_cntl_stack_offset;
 	*save_area_used_size = m->cp_hqd_wg_state_offset -
 		m->cp_hqd_cntl_stack_size;
 
-	if (copy_to_user(ctl_stack, mqd_ctl_stack, m->cp_hqd_cntl_stack_size))
-		return -EFAULT;
+	/* Control stack is not copied to user mode for GFXv10 because
+	 * it's part of the context save area that is already
+	 * accessible to user mode
+	 */
 
 	return 0;
 }