1 files changed, 14 insertions, 2 deletions

diff --git a/sys/amd64/amd64/busdma_machdep.c b/sys/amd64/amd64/busdma_machdep.c
index 348ab78c99c3..20dae8acea81 100644
--- a/sys/amd64/amd64/busdma_machdep.c
+++ b/sys/amd64/amd64/busdma_machdep.c
@@ -492,7 +492,16 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
 		}
 	}
 
+	/* 
+	 * XXX:
+	 * (dmat->alignment < dmat->maxsize) is just a quick hack; the exact
+	 * alignment guarantees of malloc need to be nailed down, and the
+	 * code below should be rewritten to take that into account.
+	 *
+	 * In the meantime, we'll panic if malloc gets it wrong.
+	 */
 	if ((dmat->maxsize <= PAGE_SIZE) &&
+	   (dmat->alignment < dmat->maxsize) &&
 	    dmat->lowaddr >= ptoa((vm_paddr_t)Maxmem)) {
 		*vaddr = malloc(dmat->maxsize, M_DEVBUF, mflags);
 	} else {
@@ -510,6 +519,8 @@ bus_dmamem_alloc(bus_dma_tag_t dmat, void** vaddr, int flags,
 		CTR4(KTR_BUSDMA, "%s: tag %p tag flags 0x%x error %d",
 		    __func__, dmat, dmat->flags, ENOMEM);
 		return (ENOMEM);
+	} else if ((uintptr_t)*vaddr & (dmat->alignment - 1)) {
+		panic("bus_dmamem_alloc failed to align memory properly.");
 	}
 	CTR4(KTR_BUSDMA, "%s: tag %p tag flags 0x%x error %d",
 	    __func__, dmat, dmat->flags, ENOMEM);
@@ -529,8 +540,9 @@ bus_dmamem_free(bus_dma_tag_t dmat, void *vaddr, bus_dmamap_t map)
 	 */
 	if (map != NULL)
 		panic("bus_dmamem_free: Invalid map freed\n");
-	if ((dmat->maxsize <= PAGE_SIZE)
-	 && dmat->lowaddr >= ptoa((vm_paddr_t)Maxmem))
+	if ((dmat->maxsize <= PAGE_SIZE) &&
+	   (dmat->alignment < dmat->maxsize) &&
+	    dmat->lowaddr >= ptoa((vm_paddr_t)Maxmem))
 		free(vaddr, M_DEVBUF);
 	else {
 		contigfree(vaddr, dmat->maxsize, M_DEVBUF);