Pull up following revision(s) (requested by maya in ticket #1350): sys/external/bsd/drm2/dist/drm/ttm/ttm_tt.c: revision 1.8 Guarantee no zero-size uao/kmem allocations via ttm. It may be that all callers guarantee no zero-size ttm objects, but I can't prove that in five minutes of browsing callers. Rather than add a KASSERT, lacking proof, we'll add a warning message so that if it does happen then it happens noisily, but we'll also prevent the bad consequences of passing zero into uao_create by rounding up to a harmless nonzero allocation.

(snj)

@@ -203,6 +203,9 @@
 	ttm->dummy_read_page = dummy_read_page;
 	ttm->state = tt_unpopulated;
 #ifdef __NetBSD__
+	WARN(size == 0, "zero-size allocation in %s, please file a NetBSD PR",
+	    __func__);	/* paranoia -- can't prove in five minutes */
+	size = MAX(size, 1);
 	ttm->swap_storage = uao_create(roundup2(size, PAGE_SIZE), 0);
 	uao_set_pgfl(ttm->swap_storage, bus_dmamem_pgfl(bdev->dmat));
 #else
@@ -245,6 +248,9 @@
 	ttm->dummy_read_page = dummy_read_page;
 	ttm->state = tt_unpopulated;
 #ifdef __NetBSD__
+	WARN(size == 0, "zero-size allocation in %s, please file a NetBSD PR",
+	    __func__);	/* paranoia -- can't prove in five minutes */
+	size = MAX(size, 1);
 	ttm->swap_storage = uao_create(roundup2(size, PAGE_SIZE), 0);
 	uao_set_pgfl(ttm->swap_storage, bus_dmamem_pgfl(bdev->dmat));
 #else