vioscsi: Fix allocation of segments

Port the logic to calculate the number of segments in virtqueue and
dmamaps from vioblk.

This fixes the virtqueue indirect descriptors being two entries too
small the dmamaps being much larger than necessary.

If the device does not support the required number of segments, refuse
to use it.

1 files changed, 20 insertions, 8 deletions

diff --git a/sys/dev/pv/vioscsi.c b/sys/dev/pv/vioscsi.c
index cb41a862413..1b8daab6502 100644
--- a/sys/dev/pv/vioscsi.c
+++ b/sys/dev/pv/vioscsi.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vioscsi.c,v 1.6 2017/05/14 12:17:47 krw Exp $	*/
+/*	$OpenBSD: vioscsi.c,v 1.7 2017/05/15 19:02:16 sf Exp $	*/
 /*
  * Copyright (c) 2013 Google Inc.
  *
@@ -40,6 +40,12 @@ enum { vioscsi_debug = 0 };
 	} while (0)
 
 
+#define MAX_XFER	MAX(MAXPHYS,MAXBSIZE)
+/* Number of DMA segments for buffers that the device must support */
+#define SEG_MAX		(MAX_XFER/PAGE_SIZE + 1)
+/* In the virtqueue, we need space for header and footer, too */
+#define ALLOC_SEGS	(SEG_MAX + 2)
+
 enum vioscsi_req_state { FREE, ALLOC, INQUEUE, DONE };
 
 struct vioscsi_req {
@@ -60,8 +66,6 @@ struct vioscsi_softc {
 	struct virtqueue	 sc_vqs[3];
 	struct vioscsi_req	*sc_reqs;
 	bus_dma_segment_t        sc_reqs_segs[1];
-
-	u_int32_t		 sc_seg_max;
 };
 
 int		 vioscsi_match(struct device *, void *, void *);
@@ -137,11 +141,14 @@ vioscsi_attach(struct device *parent, struct device *self, void *aux)
 	uint16_t max_target = virtio_read_device_config_2(vsc,
 	    VIRTIO_SCSI_CONFIG_MAX_TARGET);
 
-	sc->sc_seg_max = seg_max;
+	if (seg_max < SEG_MAX) {
+		printf("\nMax number of segments %d too small\n", seg_max);
+		goto err;
+	}
 
 	for (i = 0; i < nitems(sc->sc_vqs); i++) {
-		rv = virtio_alloc_vq(vsc, &sc->sc_vqs[i], i, MAXPHYS,
-		    1 + howmany(MAXPHYS, NBPG), vioscsi_vq_names[i]);
+		rv = virtio_alloc_vq(vsc, &sc->sc_vqs[i], i, MAX_XFER,
+		    ALLOC_SEGS, vioscsi_vq_names[i]);
 		if (rv) {
 			printf(": failed to allocate virtqueue %d\n", i);
 			return;
@@ -167,6 +174,11 @@ vioscsi_attach(struct device *parent, struct device *self, void *aux)
 	saa.saa_sc_link = &sc->sc_link;
 
 	sc->sc_scsibus = (struct scsibus *)config_found(self, &saa, scsiprint);
+	return;
+
+err:
+	vsc->sc_child = VIRTIO_CHILD_ERROR;
+	return;
 }
 
 void
@@ -442,8 +454,8 @@ vioscsi_alloc_reqs(struct vioscsi_softc *sc, struct virtio_softc *vsc,
 			printf("bus_dmamap_create vr_control failed, error  %d\n", r);
 			return 1;
 		}
-		r = bus_dmamap_create(vsc->sc_dmat, MAXPHYS, sc->sc_seg_max,
-		    MAXPHYS, 0, BUS_DMA_NOWAIT|BUS_DMA_ALLOCNOW, &vr->vr_data);
+		r = bus_dmamap_create(vsc->sc_dmat, MAX_XFER, SEG_MAX,
+		    MAX_XFER, 0, BUS_DMA_NOWAIT|BUS_DMA_ALLOCNOW, &vr->vr_data);
 		if (r != 0) {
 			printf("bus_dmamap_create vr_data failed, error %d\n", r );
 			return 1;