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virtio-ccw: commands on revision-less devices

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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>
This commit is contained in:
Cornelia Huck 2021-02-16 12:18:30 +01:00
parent 403af209db
commit 151fcdfd62
1 changed files with 14 additions and 7 deletions
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21
hw/s390x/virtio-ccw.c
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@ -327,13 +327,20 @@ static int virtio_ccw_cb(SubchDev *sch, CCW1 ccw)
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. */