Index: sys/arm64/arm64/busdma_bounce.c
===================================================================
--- sys/arm64/arm64/busdma_bounce.c
+++ sys/arm64/arm64/busdma_bounce.c
@@ -73,8 +73,8 @@
 
 struct bus_dma_tag {
 	struct bus_dma_tag_common common;
-	size_t			alloc_size;
-	size_t			alloc_alignment;
+	bus_size_t		alloc_size;
+	bus_size_t		alloc_alignment;
 	int			map_count;
 	int			bounce_flags;
 	bus_dma_segment_t	*segments;
@@ -251,8 +251,12 @@
 		 */
 		newtag->alloc_alignment = MAX(newtag->common.alignment,
 		    dcache_line_size);
-		newtag->alloc_size = roundup2(newtag->common.maxsize,
-		    dcache_line_size);
+		if (newtag->common.maxsize <
+		    (BUS_SPACE_MAXSIZE - dcache_line_size))
+			newtag->alloc_size = roundup2(newtag->common.maxsize,
+			    dcache_line_size);
+		else
+			newtag->alloc_size = newtag->common.maxsize;
 	}
 
 	if (newtag->common.lowaddr < ptoa((vm_paddr_t)Maxmem) ||
@@ -261,12 +265,6 @@
 
 	if ((flags & BUS_DMA_ALLOCNOW) != 0) {
 		struct bounce_zone *bz;
-		/*
-		 * Round size up to a full page, and add one more page because
-		 * there can always be one more boundary crossing than the
-		 * number of pages in a transfer.
-		 */
-		maxsize = roundup2(maxsize, PAGE_SIZE) + PAGE_SIZE;
 
 		/* Must bounce */
 		if ((error = alloc_bounce_zone(newtag)) != 0) {
@@ -276,7 +274,7 @@
 		bz = newtag->bounce_zone;
 
 		if (ptoa(bz->total_bpages) < maxsize) {
-			int pages;
+			bus_size_t pages;
 
 			pages = atop(maxsize) + 1 - bz->total_bpages;
 
@@ -376,7 +374,7 @@
 bounce_bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp)
 {
 	struct bounce_zone *bz;
-	int error, maxpages, pages;
+	int error, maxpages;
 
 	error = 0;
 
@@ -424,7 +422,10 @@
 		    atop(dmat->common.lowaddr));
 	if ((dmat->bounce_flags & BF_MIN_ALLOC_COMP) == 0 ||
 	    (bz->map_count > 0 && bz->total_bpages < maxpages)) {
-		pages = atop(roundup2(dmat->common.maxsize, PAGE_SIZE)) + 1;
+		bus_size_t pages;
+
+		pages = atop(dmat->common.maxsize);
+		pages = MAX(pages + 1, 1);
 		pages = MIN(maxpages - bz->total_bpages, pages);
 		pages = MAX(pages, 2);
 		if (alloc_bounce_pages(dmat, pages) < pages)
@@ -476,7 +477,7 @@
 
 /*
  * Allocate a piece of memory that can be efficiently mapped into
- * bus device space based on the constraints lited in the dma tag.
+ * bus device space based on the constraints listed in the dma tag.
  * A dmamap to for use with dmamap_load is also allocated.
  */
 static int
Index: sys/kern/subr_busdma_bounce.c
===================================================================
--- sys/kern/subr_busdma_bounce.c
+++ sys/kern/subr_busdma_bounce.c
@@ -249,7 +249,7 @@
 }
 
 static int
-alloc_bounce_pages(bus_dma_tag_t dmat, u_int numpages)
+alloc_bounce_pages(bus_dma_tag_t dmat, bus_size_t numpages)
 {
 	struct bounce_zone *bz;
 	int count;
Index: sys/riscv/riscv/busdma_bounce.c
===================================================================
--- sys/riscv/riscv/busdma_bounce.c
+++ sys/riscv/riscv/busdma_bounce.c
@@ -174,9 +174,9 @@
 		bz = newtag->bounce_zone;
 
 		if (ptoa(bz->total_bpages) < maxsize) {
-			int pages;
+			bus_size_t pages;
 
-			pages = atop(round_page(maxsize)) - bz->total_bpages;
+			pages = atop(maxsize) + 1 - bz->total_bpages;
 
 			/* Add pages to our bounce pool */
 			if (alloc_bounce_pages(newtag, pages) < pages)
@@ -261,7 +261,7 @@
 bounce_bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp)
 {
 	struct bounce_zone *bz;
-	int error, maxpages, pages;
+	int error, maxpages;
 
 	error = 0;
 
@@ -311,9 +311,11 @@
 			    atop(dmat->common.lowaddr));
 		if ((dmat->bounce_flags & BF_MIN_ALLOC_COMP) == 0 ||
 		    (bz->map_count > 0 && bz->total_bpages < maxpages)) {
+			bus_size_t pages;
+
 			pages = MAX(atop(dmat->common.maxsize), 1);
 			pages = MIN(maxpages - bz->total_bpages, pages);
-			pages = MAX(pages, 1);
+			pages = MAX(pages, 2);
 			if (alloc_bounce_pages(dmat, pages) < pages)
 				error = ENOMEM;
 			if ((dmat->bounce_flags & BF_MIN_ALLOC_COMP)
Index: sys/x86/x86/busdma_bounce.c
===================================================================
--- sys/x86/x86/busdma_bounce.c
+++ sys/x86/x86/busdma_bounce.c
@@ -130,7 +130,7 @@
 	bz = dmat->bounce_zone;
 
 	if (ptoa(bz->total_bpages) < dmat->common.maxsize) {
-		int pages;
+		bus_size_t pages;
 
 		pages = atop(dmat->common.maxsize) - bz->total_bpages;
 
@@ -273,7 +273,7 @@
 bounce_bus_dmamap_create(bus_dma_tag_t dmat, int flags, bus_dmamap_t *mapp)
 {
 	struct bounce_zone *bz;
-	int error, maxpages, pages;
+	int error, maxpages;
 
 	error = 0;
 
@@ -324,9 +324,11 @@
 			    atop(dmat->common.lowaddr));
 		if ((dmat->bounce_flags & BUS_DMA_MIN_ALLOC_COMP) == 0 ||
 		    (bz->map_count > 0 && bz->total_bpages < maxpages)) {
+			bus_size_t pages;
+
 			pages = MAX(atop(dmat->common.maxsize), 1);
 			pages = MIN(maxpages - bz->total_bpages, pages);
-			pages = MAX(pages, 1);
+			pages = MAX(pages, 2);
 			if (alloc_bounce_pages(dmat, pages) < pages)
 				error = ENOMEM;
 			if ((dmat->bounce_flags & BUS_DMA_MIN_ALLOC_COMP)