drm/amdgpu: Fix size validation for non-exclusive domains (v4)

Fix amdgpu_bo_validate_size() to check whether the TTM domain manager for the
requested memory exists, else we get a kernel oops when dereferencing "man".

v2: Make the patch standalone, i.e. not dependent on local patches.
v3: Preserve old behaviour and just check that the manager pointer is not
NULL.
v4: Complain if GTT domain requested and it is uninitialized--most likely a
bug.

Cc: Alex Deucher <[e-mail]>
Cc: Christian König <[e-mail]>
Cc: AMD Graphics <[e-mail]>
Signed-off-by: Luben Tuikov <[e-mail]>
Reviewed-by: Christian König <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 
 	/*
 	 * If GTT is part of requested domains the check must succeed to
-	 * allow fall back to GTT
+	 * allow fall back to GTT.
 	 */
 	if (domain & AMDGPU_GEM_DOMAIN_GTT) {
 		man = ttm_manager_type(&adev->mman.bdev, TTM_PL_TT);
 
-		if (size < man->size)
+		if (man && size < man->size)
 			return true;
-		else
-			goto fail;
-	}
-
-	if (domain & AMDGPU_GEM_DOMAIN_VRAM) {
+		else if (!man)
+			WARN_ON_ONCE("GTT domain requested but GTT mem manager uninitialized");
+		goto fail;
+	} else if (domain & AMDGPU_GEM_DOMAIN_VRAM) {
 		man = ttm_manager_type(&adev->mman.bdev, TTM_PL_VRAM);
 
-		if (size < man->size)
+		if (man && size < man->size)
 			return true;
-		else
-			goto fail;
+		goto fail;
 	}
-
 
 	/* TODO add more domains checks, such as AMDGPU_GEM_DOMAIN_CPU */
 	return true;