From cb927b8aee7c3993a43cb829f7341071f873857b Mon Sep 17 00:00:00 2001 From: Christian Borntraeger Date: Thu, 30 Apr 2015 17:53:13 +0200 Subject: [PATCH] s390-virtio: Accommodate guests using virtqueues too early Feature updates are not a synchronuous operation for the legacy s390-virtio transport. This transport syncs the guest feature bits (those from finalize) on the set_status hypercall. Before that qemu thinks that features are zero, which means QEMU will misbehave, e.g. it will not write the event index, even if the guest asks for it. Let's detect the case where a kick happens before the driver is ready and force sync the features. With this workaround, it is now safe to switch to the common feature bit handling code as used by all other transports. Signed-off-by: Christian Borntraeger Reviewed-by: Cornelia Huck Signed-off-by: Cornelia Huck --- hw/s390x/s390-virtio.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/hw/s390x/s390-virtio.c b/hw/s390x/s390-virtio.c index 3a1b9ee2d0..59750dbfcd 100644 --- a/hw/s390x/s390-virtio.c +++ b/hw/s390x/s390-virtio.c @@ -77,6 +77,16 @@ static int s390_virtio_hcall_notify(const uint64_t *args) if (mem > ram_size) { VirtIOS390Device *dev = s390_virtio_bus_find_vring(s390_bus, mem, &i); if (dev) { + /* + * Older kernels will use the virtqueue before setting DRIVER_OK. + * In this case the feature bits are not yet up to date, meaning + * that several funny things can happen, e.g. the guest thinks + * EVENT_IDX is on and QEMU thinks it is off. Let's force a feature + * and status sync. + */ + if (!(dev->vdev->status & VIRTIO_CONFIG_S_DRIVER_OK)) { + s390_virtio_device_update_status(dev); + } virtio_queue_notify(dev->vdev, i); } else { r = -EINVAL;