diff --git a/sys/geom/geom_dev.c b/sys/geom/geom_dev.c
index 224b5d6..9eac4b4 100644
--- a/sys/geom/geom_dev.c
+++ b/sys/geom/geom_dev.c
@@ -75,7 +75,7 @@ static struct cdevsw g_dev_cdevsw = {
 	.d_ioctl =	g_dev_ioctl,
 	.d_strategy =	g_dev_strategy,
 	.d_name =	"g_dev",
-	.d_flags =	D_DISK | D_TRACKCLOSE,
+	.d_flags =	D_DISK | D_TRACKCLOSE | D_UNMAPPED_BIO,
 };
 
 static g_taste_t g_dev_taste;
diff --git a/sys/kern/kern_conf.c b/sys/kern/kern_conf.c
index c04d1da..878593c 100644
--- a/sys/kern/kern_conf.c
+++ b/sys/kern/kern_conf.c
@@ -580,6 +580,8 @@ newdev(struct cdevsw *csw, int unit, struct cdev *si)
 			}
 		}
 	}
+	if (csw->d_flags & D_UNMAPPED_BIO)
+		si->si_flags |= SI_UNMAPPED_BIO;
 	si->si_drv0 = unit;
 	si->si_devsw = csw;
 	LIST_INSERT_HEAD(&csw->d_devs, si, si_list);
diff --git a/sys/kern/kern_physio.c b/sys/kern/kern_physio.c
index 922ebb6..499e524 100644
--- a/sys/kern/kern_physio.c
+++ b/sys/kern/kern_physio.c
@@ -91,11 +91,15 @@ physio(struct cdev *dev, struct uio *uio, int ioflag)
 
 			bp->b_blkno = btodb(bp->b_offset);
 
-			if (uio->uio_segflg == UIO_USERSPACE)
-				if (vmapbuf(bp, 0) < 0) {
+			if (uio->uio_segflg == UIO_USERSPACE) {
+				int unmapped;
+
+				unmapped = dev->si_flags & D_UNMAPPED_BIO;
+				if (vmapbuf(bp, unmapped == 0) < 0) {
 					error = EFAULT;
 					goto doerror;
 				}
+			}
 
 			dev_strategy(dev, bp);
 			if (uio->uio_rw == UIO_READ)
diff --git a/sys/sys/conf.h b/sys/sys/conf.h
index e818722..5c0dbec 100644
--- a/sys/sys/conf.h
+++ b/sys/sys/conf.h
@@ -61,6 +61,7 @@ struct cdev {
 #define	SI_CHILD	0x0010	/* child of another struct cdev **/
 #define	SI_DUMPDEV	0x0080	/* is kernel dumpdev */
 #define	SI_CLONELIST	0x0200	/* on a clone list */
+#define	SI_UNMAPPED_BIO 0x0400  /* device can handle unmapped IO */
 	struct timespec	si_atime;
 	struct timespec	si_ctime;
 	struct timespec	si_mtime;
@@ -167,6 +168,7 @@ typedef int dumper_t(
 #define	D_MMAP_ANON	0x00100000	/* special treatment in vm_mmap.c */
 #define	D_NEEDGIANT	0x00400000	/* driver want Giant */
 #define	D_NEEDMINOR	0x00800000	/* driver uses clone_create() */
+#define	D_UNMAPPED_BIO  0x01000000	/* d_strategy can accept unmapped IO */
 
 /*
  * Version numbers.