Patchwork [39/43] virtio-scsi: Fix subtle (guest) endian bug

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Submitter Michael Roth
Date Dec. 3, 2012, 10:44 p.m.
Message ID <>
Download mbox | patch
Permalink /patch/203476/
State New
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Michael Roth - Dec. 3, 2012, 10:44 p.m.
From: David Gibson <>

The virtio-scsi config space is, by specification, in guest endian (which
is ill-defined, but there you go).  In virtio_scsi_get_config() we set up
all the fields in there, using stl_raw().  Which is a problem for the
max_channel and max_target fields, which are 16-bit, not 32-bit.  For
little-endian targets we get away with it by accident, since the first
two bytes will still be correct, and the extra two bytes written (with
zeroes) will be overwritten correctly by the next store.

But for big-endian guests, this means the max_target field ends up as zero,
which means the guest will only recognize a single disk on the virtio-scsi
bus.  This patch fixes the problem.

Cc: Paolo Bonzini <>
Cc: Paul 'Rusty' Russell <>
Signed-off-by: David Gibson <>
Signed-off-by: Paolo Bonzini <>
(cherry picked from commit 863d1050c96cff91dd478767c0da9cc288575919)

Signed-off-by: Michael Roth <>
 hw/virtio-scsi.c |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)


diff --git a/hw/virtio-scsi.c b/hw/virtio-scsi.c
index c6d5290..5fcbdd8 100644
--- a/hw/virtio-scsi.c
+++ b/hw/virtio-scsi.c
@@ -534,8 +534,8 @@  static void virtio_scsi_get_config(VirtIODevice *vdev,
     stl_raw(&scsiconf->event_info_size, sizeof(VirtIOSCSIEvent));
     stl_raw(&scsiconf->sense_size, s->sense_size);
     stl_raw(&scsiconf->cdb_size, s->cdb_size);
-    stl_raw(&scsiconf->max_channel, VIRTIO_SCSI_MAX_CHANNEL);
-    stl_raw(&scsiconf->max_target, VIRTIO_SCSI_MAX_TARGET);
+    stw_raw(&scsiconf->max_channel, VIRTIO_SCSI_MAX_CHANNEL);
+    stw_raw(&scsiconf->max_target, VIRTIO_SCSI_MAX_TARGET);
     stl_raw(&scsiconf->max_lun, VIRTIO_SCSI_MAX_LUN);