--- //depot/user/jhb/boot/sys/boot/i386/common/drv.c	2014-08-27 19:53:55.000000000 0000
+++ /home/jhb/work/p4/boot/sys/boot/i386/common/drv.c	2014-08-27 19:53:55.000000000 0000
@@ -54,11 +54,37 @@
 
 #ifndef USE_XREAD
 static struct edd_packet packet;
+static char bounce_buffer[512];
+
+static int drvread_one(struct dsk *, void *, daddr_t, unsigned);
 #endif
 
 int
 drvread(struct dsk *dskp, void *buf, daddr_t lba, unsigned nblk)
 {
+#ifndef USE_XREAD
+	int i;
+
+	/* If the buffer is below 1MB, pass it through directly. */
+	if (VTOP((char *)buf + nblk * 512) >> 20 == 0)
+		return (drvread_one(dskp, buf, lba, nblk));
+
+	/*
+	 * Use the bounce buffer to transfer the data one sector at a
+	 * time.
+	 */
+	for (i = 0; i < nblk; i++) {
+		if (drvread_one(dskp, bounce_buffer, lba + i, 1) < 0)
+			return (-1);
+		memcpy((char *)buf + 512 * i, bounce_buffer, 512);
+	}
+	return (0);
+}
+
+static int
+drvread_one(struct dsk *dskp, void *buf, daddr_t lba, unsigned nblk)
+{
+#endif
 	static unsigned c = 0x2d5c7c2f;
 	int retries = 3;