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vhost: enable vrings in vhost_dev_start() for vhost-user devices

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Commit 02b61f38d3 ("hw/virtio: incorporate backend features in features")
properly negotiates VHOST_USER_F_PROTOCOL_FEATURES with the vhost-user
backend, but we forgot to enable vrings as specified in
docs/interop/vhost-user.rst:

    If ``VHOST_USER_F_PROTOCOL_FEATURES`` has not been negotiated, the
    ring starts directly in the enabled state.

    If ``VHOST_USER_F_PROTOCOL_FEATURES`` has been negotiated, the ring is
    initialized in a disabled state and is enabled by
    ``VHOST_USER_SET_VRING_ENABLE`` with parameter 1.

Some vhost-user front-ends already did this by calling
vhost_ops.vhost_set_vring_enable() directly:
- backends/cryptodev-vhost.c
- hw/net/virtio-net.c
- hw/virtio/vhost-user-gpio.c

But most didn't do that, so we would leave the vrings disabled and some
backends would not work. We observed this issue with the rust version of
virtiofsd [1], which uses the event loop [2] provided by the
vhost-user-backend crate where requests are not processed if vring is
not enabled.

Let's fix this issue by enabling the vrings in vhost_dev_start() for
vhost-user front-ends that don't already do this directly. Same thing
also in vhost_dev_stop() where we disable vrings.

[1] https://gitlab.com/virtio-fs/virtiofsd
[2] 240fc2966/crates/vhost-user-backend/src/event_loop.rs (L217)

Fixes: 02b61f38d3 ("hw/virtio: incorporate backend features in features")
Reported-by: German Maglione <gmaglione@redhat.com>
Tested-by: German Maglione <gmaglione@redhat.com>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Acked-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
Message-Id: <20221123131630.52020-1-sgarzare@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Message-Id: <20221130112439.2527228-3-alex.bennee@linaro.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Stefano Garzarella 2022-11-30 11:24:36 +00:00 • committed by Michael S. Tsirkin
parent 523e40022f
commit 4daa5054c5
13 changed files with 67 additions and 31 deletions
Download patch file Download diff file Expand all files Collapse all files

4
hw/virtio/vhost-user-rng.c
View file

@ -47,7 +47,7 @@ static void vu_rng_start(VirtIODevice *vdev)
}
rng->vhost_dev.acked_features = vdev->guest_features;
ret = vhost_dev_start(&rng->vhost_dev, vdev);
ret = vhost_dev_start(&rng->vhost_dev, vdev, true);
if (ret < 0) {
error_report("Error starting vhost-user-rng: %d", -ret);
goto err_guest_notifiers;
@ -81,7 +81,7 @@ static void vu_rng_stop(VirtIODevice *vdev)
return;
}
vhost_dev_stop(&rng->vhost_dev, vdev);
vhost_dev_stop(&rng->vhost_dev, vdev, true);
ret = k->set_guest_notifiers(qbus->parent, rng->vhost_dev.nvqs, false);
if (ret < 0) {