| Message ID | 1459267981-23408-4-git-send-email-stefanha@redhat.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 29 Mar 2016 17:12:55 +0100 Stefan Hajnoczi <stefanha@redhat.com> wrote: > QEMU prints an error message and exits when the device enters an invalid > state. Terminating the process is heavy-handed. The guest may still be > able to function even if there is a bug in a virtio guest driver. > > Moreover, exiting is a bug in nested virtualization where a nested guest > could DoS other nested guests by killing a pass-through virtio device. > I don't think this configuration is possible today but it is likely in > the future. > > If the broken flag is set, do not process virtqueues or write back used > descriptors. The broken flag can be cleared again by resetting the > device. > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > --- > hw/virtio/virtio.c | 39 +++++++++++++++++++++++++++++++++++++++ > include/hw/virtio/virtio.h | 3 +++ > 2 files changed, 42 insertions(+) > +void GCC_FMT_ATTR(2, 3) virtio_error(VirtIODevice *vdev, const char *fmt, ...) > +{ > + va_list ap; > + > + va_start(ap, fmt); > + error_vreport(fmt, ap); > + va_end(ap); > + > + vdev->broken = true; > + > + if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) { > + vdev->status |= VIRTIO_CONFIG_S_NEEDS_RESET; virtio_set_status()? > + virtio_notify_config(vdev); > + } > +} > + > static void virtio_device_realize(DeviceState *dev, Error **errp) > { > VirtIODevice *vdev = VIRTIO_DEVICE(dev); > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > index 2b5b248..1565e53 100644 > --- a/include/hw/virtio/virtio.h > +++ b/include/hw/virtio/virtio.h > @@ -87,6 +87,7 @@ struct VirtIODevice > VirtQueue *vq; > uint16_t device_id; > bool vm_running; > + bool broken; /* device in invalid state, needs reset */ I'm wondering whether there's a sane way to track the broken state via the NEEDS_RESET status bit instead. We'd probably want to filter out this bit and not expose it to legacy drivers; but as the status field is migrated anyway, we might be able to avoid a subsection for migration.
On Tue, Mar 29, 2016 at 06:58:03PM +0200, Cornelia Huck wrote: > On Tue, 29 Mar 2016 17:12:55 +0100 > Stefan Hajnoczi <stefanha@redhat.com> wrote: > > diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h > > index 2b5b248..1565e53 100644 > > --- a/include/hw/virtio/virtio.h > > +++ b/include/hw/virtio/virtio.h > > @@ -87,6 +87,7 @@ struct VirtIODevice > > VirtQueue *vq; > > uint16_t device_id; > > bool vm_running; > > + bool broken; /* device in invalid state, needs reset */ > > I'm wondering whether there's a sane way to track the broken state via > the NEEDS_RESET status bit instead. We'd probably want to filter out > this bit and not expose it to legacy drivers; but as the status field > is migrated anyway, we might be able to avoid a subsection for > migration. If we set the non-VIRTIO 1.0 bit and migrate to an old QEMU that doesn't filter the bit then the guest will see it. Therefore I'm in favor of keeping vdev->broken separate from the status bit. The subsection only needs to be sent when the bit is set. Only migration of a broken device to an old QEMU will fail. All other cases continue to work so the subsection doesn't impose much incompatibility. Stefan
On Tue, Mar 29, 2016 at 06:58:03PM +0200, Cornelia Huck wrote: > On Tue, 29 Mar 2016 17:12:55 +0100 > Stefan Hajnoczi <stefanha@redhat.com> wrote: > > > QEMU prints an error message and exits when the device enters an invalid > > state. Terminating the process is heavy-handed. The guest may still be > > able to function even if there is a bug in a virtio guest driver. > > > > Moreover, exiting is a bug in nested virtualization where a nested guest > > could DoS other nested guests by killing a pass-through virtio device. > > I don't think this configuration is possible today but it is likely in > > the future. > > > > If the broken flag is set, do not process virtqueues or write back used > > descriptors. The broken flag can be cleared again by resetting the > > device. > > > > Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> > > --- > > hw/virtio/virtio.c | 39 +++++++++++++++++++++++++++++++++++++++ > > include/hw/virtio/virtio.h | 3 +++ > > 2 files changed, 42 insertions(+) > > > +void GCC_FMT_ATTR(2, 3) virtio_error(VirtIODevice *vdev, const char *fmt, ...) > > +{ > > + va_list ap; > > + > > + va_start(ap, fmt); > > + error_vreport(fmt, ap); > > + va_end(ap); > > + > > + vdev->broken = true; > > + > > + if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) { > > + vdev->status |= VIRTIO_CONFIG_S_NEEDS_RESET; > > virtio_set_status()? Will fix in next revision
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c index de8a3b3..ff2c736 100644 --- a/hw/virtio/virtio.c +++ b/hw/virtio/virtio.c @@ -276,6 +276,10 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem, virtqueue_unmap_sg(vq, elem, len); + if (unlikely(vq->vdev->broken)) { + return; + } + idx = (idx + vq->used_idx) % vq->vring.num; uelem.id = elem->index; @@ -286,6 +290,12 @@ void virtqueue_fill(VirtQueue *vq, const VirtQueueElement *elem, void virtqueue_flush(VirtQueue *vq, unsigned int count) { uint16_t old, new; + + if (unlikely(vq->vdev->broken)) { + vq->inuse -= count; + return; + } + /* Make sure buffer is written before we update index. */ smp_wmb(); trace_virtqueue_flush(vq, count); @@ -546,6 +556,9 @@ void *virtqueue_pop(VirtQueue *vq, size_t sz) struct iovec iov[VIRTQUEUE_MAX_SIZE]; VRingDesc desc; + if (unlikely(vdev->broken)) { + return NULL; + } if (virtio_queue_empty(vq)) { return NULL; } @@ -705,6 +718,10 @@ static void virtio_notify_vector(VirtIODevice *vdev, uint16_t vector) BusState *qbus = qdev_get_parent_bus(DEVICE(vdev)); VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus); + if (unlikely(vdev->broken)) { + return; + } + if (k->notify) { k->notify(qbus->parent, vector); } @@ -788,6 +805,7 @@ void virtio_reset(void *opaque) k->reset(vdev); } + vdev->broken = false; vdev->guest_features = 0; vdev->queue_sel = 0; vdev->status = 0; @@ -1091,6 +1109,10 @@ void virtio_queue_notify_vq(VirtQueue *vq) if (vq->vring.desc && vq->handle_output) { VirtIODevice *vdev = vq->vdev; + if (unlikely(vdev->broken)) { + return; + } + trace_virtio_queue_notify(vdev, vq - vdev->vq, vq); vq->handle_output(vdev, vq); } @@ -1661,6 +1683,7 @@ void virtio_init(VirtIODevice *vdev, const char *name, vdev->config_vector = VIRTIO_NO_VECTOR; vdev->vq = g_malloc0(sizeof(VirtQueue) * VIRTIO_QUEUE_MAX); vdev->vm_running = runstate_is_running(); + vdev->broken = false; for (i = 0; i < VIRTIO_QUEUE_MAX; i++) { vdev->vq[i].vector = VIRTIO_NO_VECTOR; vdev->vq[i].vdev = vdev; @@ -1829,6 +1852,22 @@ void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name) vdev->bus_name = g_strdup(bus_name); } +void GCC_FMT_ATTR(2, 3) virtio_error(VirtIODevice *vdev, const char *fmt, ...) +{ + va_list ap; + + va_start(ap, fmt); + error_vreport(fmt, ap); + va_end(ap); + + vdev->broken = true; + + if (virtio_vdev_has_feature(vdev, VIRTIO_F_VERSION_1)) { + vdev->status |= VIRTIO_CONFIG_S_NEEDS_RESET; + virtio_notify_config(vdev); + } +} + static void virtio_device_realize(DeviceState *dev, Error **errp) { VirtIODevice *vdev = VIRTIO_DEVICE(dev); diff --git a/include/hw/virtio/virtio.h b/include/hw/virtio/virtio.h index 2b5b248..1565e53 100644 --- a/include/hw/virtio/virtio.h +++ b/include/hw/virtio/virtio.h @@ -87,6 +87,7 @@ struct VirtIODevice VirtQueue *vq; uint16_t device_id; bool vm_running; + bool broken; /* device in invalid state, needs reset */ VMChangeStateEntry *vmstate; char *bus_name; uint8_t device_endian; @@ -135,6 +136,8 @@ void virtio_init(VirtIODevice *vdev, const char *name, uint16_t device_id, size_t config_size); void virtio_cleanup(VirtIODevice *vdev); +void virtio_error(VirtIODevice *vdev, const char *fmt, ...) GCC_FMT_ATTR(2, 3); + /* Set the child bus name. */ void virtio_device_set_child_bus_name(VirtIODevice *vdev, char *bus_name);
QEMU prints an error message and exits when the device enters an invalid state. Terminating the process is heavy-handed. The guest may still be able to function even if there is a bug in a virtio guest driver. Moreover, exiting is a bug in nested virtualization where a nested guest could DoS other nested guests by killing a pass-through virtio device. I don't think this configuration is possible today but it is likely in the future. If the broken flag is set, do not process virtqueues or write back used descriptors. The broken flag can be cleared again by resetting the device. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> --- hw/virtio/virtio.c | 39 +++++++++++++++++++++++++++++++++++++++ include/hw/virtio/virtio.h | 3 +++ 2 files changed, 42 insertions(+)