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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
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6
include/hw/virtio/vhost.h
View file

@ -184,24 +184,26 @@ static inline bool vhost_dev_is_started(struct vhost_dev *hdev)
* vhost_dev_start() - start the vhost device
* @hdev: common vhost_dev structure
* @vdev: the VirtIODevice structure
* @vrings: true to have vrings enabled in this call
*
* Starts the vhost device. From this point VirtIO feature negotiation
* can start and the device can start processing VirtIO transactions.
*
* Return: 0 on success, < 0 on error.
*/
int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev);
int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings);
/**
* vhost_dev_stop() - stop the vhost device
* @hdev: common vhost_dev structure
* @vdev: the VirtIODevice structure
* @vrings: true to have vrings disabled in this call
*
* Stop the vhost device. After the device is stopped the notifiers
* can be disabled (@vhost_dev_disable_notifiers) and the device can
* be torn down (@vhost_dev_cleanup).
*/
void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev);
void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool vrings);
/**
* DOC: vhost device configuration handling