On 10.07.24 18:28, Stefan Hajnoczi wrote:
On Wed, 10 Jul 2024 at 13:25, Hanna Czenczek<hre...@redhat.com> wrote:
Requiring `vhost_started` to be true for resetting vhost devices in
`virtio_reset()` seems like the wrong condition: Most importantly, the
preceding `virtio_set_status(vdev, 0)` call will (for vhost devices) end
up in `vhost_dev_stop()` (through vhost devices' `.set_status`
implementations), setting `vdev->vhost_started = false`. Therefore, the
gated `vhost_reset_device()` call is unreachable.
`vhost_started` is not documented, so it is hard to say what exactly it
is supposed to mean, but judging from the fact that `vhost_dev_start()`
sets it and `vhost_dev_stop()` clears it, it seems like it indicates
whether there is a vhost back-end, and whether that back-end is
currently running and processing virtio requests.
Making a reset conditional on whether the vhost back-end is processing
virtio requests seems wrong; in fact, it is probably better to reset it
only when it is not currently processing requests, which is exactly the
current order of operations in `virtio_reset()`: First, the back-end is
stopped through `virtio_set_status(vdev, 0)`, then we want to send a
reset.
Therefore, we should drop the `vhost_started` condition, but in its
stead we then have to verify that we can indeed send a reset to this
vhost device, by not just checking `k->get_vhost != NULL` (introduced by
commit 95e1019a4a9), but also that the vhost back-end is connected
(`hdev = k->get_vhost(); hdev != NULL && hdev->vhost_ops != NULL`).
Signed-off-by: Hanna Czenczek<hre...@redhat.com>
I think an additional SET_STATUS 0 call is made to the vDPA vhost
backend after this patch, but that seems fine.
Reviewed-by: Stefan Hajnoczi<stefa...@redhat.com>
Thanks! I agree that double-sending SET_STATUS with the same value
should be fine.The virtio specification states: “The device status field
starts out as 0, and is reinitialized to 0 by the device during reset.”
– I interpret that to mean that (re-)setting the field to 0 is always
OK. Hanna
---
hw/virtio/virtio.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/hw/virtio/virtio.c b/hw/virtio/virtio.c
index 893a072c9d..4410d62126 100644
--- a/hw/virtio/virtio.c
+++ b/hw/virtio/virtio.c
@@ -2146,8 +2146,12 @@ void virtio_reset(void *opaque)
vdev->device_endian = virtio_default_endian();
}
- if (vdev->vhost_started && k->get_vhost) {
- vhost_reset_device(k->get_vhost(vdev));
+ if (k->get_vhost) {
+ struct vhost_dev *hdev = k->get_vhost(vdev);
+ /* Only reset when vhost back-end is connected */
+ if (hdev && hdev->vhost_ops) {
+ vhost_reset_device(hdev);
+ }
}
if (k->reset) {
--
2.45.2
