diff --git a/stand/efi/loader/conf.c b/stand/efi/loader/conf.c
--- a/stand/efi/loader/conf.c
+++ b/stand/efi/loader/conf.c
@@ -35,6 +35,10 @@
 
 extern struct devsw vdisk_dev;
 
+#ifdef MD_IMAGE_SIZE
+extern struct devsw md_dev;
+#endif
+
 struct devsw *devsw[] = {
 	&efipart_fddev,
 	&efipart_cddev,
@@ -46,6 +50,9 @@
 	&vdisk_dev,
 #ifdef EFI_ZFS_BOOT
 	&zfs_dev,
+#endif
+#ifdef MD_IMAGE_SIZE
+	&md_dev,
 #endif
 	NULL
 };
diff --git a/stand/efi/loader/main.c b/stand/efi/loader/main.c
--- a/stand/efi/loader/main.c
+++ b/stand/efi/loader/main.c
@@ -296,6 +296,21 @@
 }
 #endif
 
+#ifdef MD_IMAGE_SIZE
+static bool
+probe_md_currdev(void)
+{
+	extern struct devsw md_dev;
+	bool rv;
+
+	set_currdev_devsw(&md_dev, 0);
+	rv = sanity_check_currdev();
+	if (!rv)
+		printf("MD not present\n");
+	return (rv);
+}
+#endif
+
 static bool
 try_as_currdev(pdinfo_t *hd, pdinfo_t *pp)
 {
@@ -569,6 +584,15 @@
 	}
 #endif /* EFI_ZFS_BOOT */
 
+#ifdef MD_IMAGE_SIZE
+	/*
+	 * If there is an embedded MD, try to use that.
+	 */
+	printf("Trying MD\n");
+	if (probe_md_currdev())
+		return (0);
+#endif /* MD_IMAGE_SIZE */
+
 	/*
 	 * Try to find the block device by its handle based on the
 	 * image we're booting. If we can't find a sane partition,
diff --git a/stand/man/loader.8 b/stand/man/loader.8
--- a/stand/man/loader.8
+++ b/stand/man/loader.8
@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd October 2, 2020
+.Dd April 7, 2021
 .Dt LOADER 8
 .Os
 .Sh NAME
@@ -987,6 +987,23 @@
 for details.
 In order for this to be effective, one should also configure the firmware
 (BIOS or UEFI) to prevent booting from unauthorized devices.
+.Sh MD
+Memory disk (MD) can be used when the
+.Nm
+was compiled with
+.Va MD_IMAGE_SIZE .
+The size of the memory disk is determined by
+.Va MD_IMAGE_SIZE .
+If MD available, a file system can be embedded into the
+.Nm
+with
+.Pa /sys/tools/embed_mfs.sh .
+Then, MD will be probed and be set to
+.Va currdev
+during initialization.
+.Pp
+Currently, MD is only supported in
+.Xr loader.efi 8 .
 .Sh FILES
 .Bl -tag -width /usr/share/examples/bootforth/ -compact
 .It Pa /boot/loader