virtio-ccw: commands on revision-less devices
The virtio standard specifies that any non-transitional device must
reject commands prior to revision setting (which we do). Devices
that are transitional need to assume revision 0 (legacy) if the
driver sends a non-revision-setting command first in order to
support legacy drivers. We neglected to do the latter.
Fortunately, nearly everything worked as intended anyway; the only
problem was not properly rejecting revision setting after some other
command had been issued. Easy to fix by setting revision to 0 if
we see a non-revision command on a legacy-capable revision-less
device.
Found by code inspection, not observed in the wild.
Signed-off-by: Cornelia Huck <cohuck@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Message-Id: <20210216111830.1087847-1-cohuck@redhat.com>
diff --git a/hw/s390x/virtio-ccw.c b/hw/s390x/virtio-ccw.c
index 4582e94..06c0605 100644
--- a/hw/s390x/virtio-ccw.c
+++ b/hw/s390x/virtio-ccw.c
@@ -327,13 +327,20 @@
ccw.cmd_code);
check_len = !((ccw.flags & CCW_FLAG_SLI) && !(ccw.flags & CCW_FLAG_DC));
- if (dev->force_revision_1 && dev->revision < 0 &&
- ccw.cmd_code != CCW_CMD_SET_VIRTIO_REV) {
- /*
- * virtio-1 drivers must start with negotiating to a revision >= 1,
- * so post a command reject for all other commands
- */
- return -ENOSYS;
+ if (dev->revision < 0 && ccw.cmd_code != CCW_CMD_SET_VIRTIO_REV) {
+ if (dev->force_revision_1) {
+ /*
+ * virtio-1 drivers must start with negotiating to a revision >= 1,
+ * so post a command reject for all other commands
+ */
+ return -ENOSYS;
+ } else {
+ /*
+ * If the driver issues any command that is not SET_VIRTIO_REV,
+ * we'll have to operate the device in legacy mode.
+ */
+ dev->revision = 0;
+ }
}
/* Look at the command. */
