[backport of commit 182f709c5cff683e6732d04c78e328de0532284f to 4.14-stable; context diff in second hunk]

CCW_CMD_READ_STATUS was introduced with revision 2 of virtio-ccw, and drivers should only rely on it being implemented when they negotiated at least that revision with the device.

However, virtio_ccw_get_status() issued READ_STATUS for any device operating at least at revision 1. If the device accepts READ_STATUS regardless of the negotiated revision (which some implementations like QEMU do, even though the spec currently does not allow it), everything works as intended. While a device rejecting the command should also be handled gracefully, we will not be able to see any changes the device makes to the status, such as setting NEEDS_RESET or setting the status to zero after a completed reset.

We negotiated the revision to at most 1, as we never bumped the maximum revision; let's do that now and properly send READ_STATUS only if we are operating at least at revision 2.

Cc: stable@vger.kernel.org Fixes: 7d3ce5ab9430 ("virtio/s390: support READ_STATUS command for virtio-ccw") Reviewed-by: Halil Pasic pasic@linux.ibm.com Signed-off-by: Cornelia Huck cohuck@redhat.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com Link: https://lore.kernel.org/r/20210216110645.1087321-1-cohuck@redhat.com Signed-off-by: Vasily Gorbik gor@linux.ibm.com Signed-off-by: Cornelia Huck cohuck@redhat.com --- drivers/s390/virtio/virtio_ccw.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c index f9cf676a0469..56794b13bb12 100644 --- a/drivers/s390/virtio/virtio_ccw.c +++ b/drivers/s390/virtio/virtio_ccw.c @@ -106,7 +106,7 @@ struct virtio_rev_info { };

/* the highest virtio-ccw revision we support */ -#define VIRTIO_CCW_REV_MAX 1 +#define VIRTIO_CCW_REV_MAX 2

struct virtio_ccw_vq_info { struct virtqueue *vq; @@ -911,7 +911,7 @@ static u8 virtio_ccw_get_status(struct virtio_device *vdev) u8 old_status = *vcdev->status; struct ccw1 *ccw;

- if (vcdev->revision < 1) + if (vcdev->revision < 2) return *vcdev->status;

ccw = kzalloc(sizeof(*ccw), GFP_DMA | GFP_KERNEL);