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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: virtualization-bounces@lists.linux-foundation.org Sender: "Virtualization" On Fri, 12 Feb 2021 18:04:11 +0100 Cornelia Huck wrote: > 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 it is > free to do), So, looking at the standard again, the device is actually required to reject the READ_STATUS if only rev 1 had been negotiated... regardless of that, I don't think we should change QEMU's behaviour, as it would affect existing guests (they would lose access to the status bits as observed by the device, including DEVICE_NEEDS_RESET.) > everything works as intended; a device rejecting the > command should also be handled gracefully. For correctness, we > should really limit the command to revision 2 or higher, though. > > We also negotiated the revision to at most 1, as we never bumped > the maximum revision; let's do that now. > > Fixes: 7d3ce5ab9430 ("virtio/s390: support READ_STATUS command for virtio-ccw") > Signed-off-by: Cornelia Huck > --- > > QEMU does not fence off READ_STATUS for revisions < 2, which is probably > why we never noticed this. I'm not aware of other hypervisors that do > fence it off, nor any that cannot deal properly with an unknown command. > > Not sure whether this is stable worthy? Maybe it is, given the MUST reject clause in the standard? > > --- > 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 5730572b52cd..54e686dca6de 100644 > --- a/drivers/s390/virtio/virtio_ccw.c > +++ b/drivers/s390/virtio/virtio_ccw.c > @@ -117,7 +117,7 @@ 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; > @@ -952,7 +952,7 @@ static u8 virtio_ccw_get_status(struct virtio_device *vdev) > u8 old_status = vcdev->dma_area->status; > struct ccw1 *ccw; > > - if (vcdev->revision < 1) > + if (vcdev->revision < 2) > return vcdev->dma_area->status; > > ccw = ccw_device_dma_zalloc(vcdev->cdev, sizeof(*ccw)); _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization