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Re: [PATCH for-7.2] vhost: enable vrings in vhost_dev_start() for vhost-


From: Michael S. Tsirkin
Subject: Re: [PATCH for-7.2] vhost: enable vrings in vhost_dev_start() for vhost-user devices
Date: Thu, 24 Nov 2022 01:50:19 -0500

On Thu, Nov 24, 2022 at 12:19:25AM +0000, Raphael Norwitz wrote:
> 
> > On Nov 23, 2022, at 8:16 AM, Stefano Garzarella <sgarzare@redhat.com> wrote:
> > 
> > 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
> 
> To simplify why not rather change these devices to use the new semantics?

Granted this is already scary enough for this release.

> > 
> > 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] 
> > https://github.com/rust-vmm/vhost/blob/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>
> 
> Looks good for vhost-user-blk/vhost-user-scsi.
> 
> Acked-by: Raphael Norwitz <raphael.norwitz@nutanix.com>
> 
> > ---
> > include/hw/virtio/vhost.h      |  6 +++--
> > backends/cryptodev-vhost.c     |  4 ++--
> > backends/vhost-user.c          |  4 ++--
> > hw/block/vhost-user-blk.c      |  4 ++--
> > hw/net/vhost_net.c             |  8 +++----
> > hw/scsi/vhost-scsi-common.c    |  4 ++--
> > hw/virtio/vhost-user-fs.c      |  4 ++--
> > hw/virtio/vhost-user-gpio.c    |  4 ++--
> > hw/virtio/vhost-user-i2c.c     |  4 ++--
> > hw/virtio/vhost-user-rng.c     |  4 ++--
> > hw/virtio/vhost-vsock-common.c |  4 ++--
> > hw/virtio/vhost.c              | 44 ++++++++++++++++++++++++++++++----
> > hw/virtio/trace-events         |  4 ++--
> > 13 files changed, 67 insertions(+), 31 deletions(-)
> > 
> > diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> > index 353252ac3e..67a6807fac 100644
> > --- a/include/hw/virtio/vhost.h
> > +++ b/include/hw/virtio/vhost.h
> > @@ -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
> > diff --git a/backends/cryptodev-vhost.c b/backends/cryptodev-vhost.c
> > index bc13e466b4..572f87b3be 100644
> > --- a/backends/cryptodev-vhost.c
> > +++ b/backends/cryptodev-vhost.c
> > @@ -94,7 +94,7 @@ cryptodev_vhost_start_one(CryptoDevBackendVhost *crypto,
> >         goto fail_notifiers;
> >     }
> > 
> > -    r = vhost_dev_start(&crypto->dev, dev);
> > +    r = vhost_dev_start(&crypto->dev, dev, false);
> >     if (r < 0) {
> >         goto fail_start;
> >     }
> > @@ -111,7 +111,7 @@ static void
> > cryptodev_vhost_stop_one(CryptoDevBackendVhost *crypto,
> >                                  VirtIODevice *dev)
> > {
> > -    vhost_dev_stop(&crypto->dev, dev);
> > +    vhost_dev_stop(&crypto->dev, dev, false);
> >     vhost_dev_disable_notifiers(&crypto->dev, dev);
> > }
> > 
> > diff --git a/backends/vhost-user.c b/backends/vhost-user.c
> > index 5dedb2d987..7bfcaef976 100644
> > --- a/backends/vhost-user.c
> > +++ b/backends/vhost-user.c
> > @@ -85,7 +85,7 @@ vhost_user_backend_start(VhostUserBackend *b)
> >     }
> > 
> >     b->dev.acked_features = b->vdev->guest_features;
> > -    ret = vhost_dev_start(&b->dev, b->vdev);
> > +    ret = vhost_dev_start(&b->dev, b->vdev, true);
> >     if (ret < 0) {
> >         error_report("Error start vhost dev");
> >         goto err_guest_notifiers;
> > @@ -120,7 +120,7 @@ vhost_user_backend_stop(VhostUserBackend *b)
> >         return;
> >     }
> > 
> > -    vhost_dev_stop(&b->dev, b->vdev);
> > +    vhost_dev_stop(&b->dev, b->vdev, true);
> > 
> >     if (k->set_guest_notifiers) {
> >         ret = k->set_guest_notifiers(qbus->parent,
> > diff --git a/hw/block/vhost-user-blk.c b/hw/block/vhost-user-blk.c
> > index 0d5190accf..1177064631 100644
> > --- a/hw/block/vhost-user-blk.c
> > +++ b/hw/block/vhost-user-blk.c
> > @@ -178,7 +178,7 @@ static int vhost_user_blk_start(VirtIODevice *vdev, 
> > Error **errp)
> >     }
> > 
> >     s->dev.vq_index_end = s->dev.nvqs;
> > -    ret = vhost_dev_start(&s->dev, vdev);
> > +    ret = vhost_dev_start(&s->dev, vdev, true);
> >     if (ret < 0) {
> >         error_setg_errno(errp, -ret, "Error starting vhost");
> >         goto err_guest_notifiers;
> > @@ -213,7 +213,7 @@ static void vhost_user_blk_stop(VirtIODevice *vdev)
> >         return;
> >     }
> > 
> > -    vhost_dev_stop(&s->dev, vdev);
> > +    vhost_dev_stop(&s->dev, vdev, true);
> > 
> >     ret = k->set_guest_notifiers(qbus->parent, s->dev.nvqs, false);
> >     if (ret < 0) {
> > diff --git a/hw/net/vhost_net.c b/hw/net/vhost_net.c
> > index 26e4930676..043058ff43 100644
> > --- a/hw/net/vhost_net.c
> > +++ b/hw/net/vhost_net.c
> > @@ -259,7 +259,7 @@ static int vhost_net_start_one(struct vhost_net *net,
> >         goto fail_notifiers;
> >     }
> > 
> > -    r = vhost_dev_start(&net->dev, dev);
> > +    r = vhost_dev_start(&net->dev, dev, false);
> >     if (r < 0) {
> >         goto fail_start;
> >     }
> > @@ -308,7 +308,7 @@ fail:
> >     if (net->nc->info->poll) {
> >         net->nc->info->poll(net->nc, true);
> >     }
> > -    vhost_dev_stop(&net->dev, dev);
> > +    vhost_dev_stop(&net->dev, dev, false);
> > fail_start:
> >     vhost_dev_disable_notifiers(&net->dev, dev);
> > fail_notifiers:
> > @@ -329,7 +329,7 @@ static void vhost_net_stop_one(struct vhost_net *net,
> >     if (net->nc->info->poll) {
> >         net->nc->info->poll(net->nc, true);
> >     }
> > -    vhost_dev_stop(&net->dev, dev);
> > +    vhost_dev_stop(&net->dev, dev, false);
> >     if (net->nc->info->stop) {
> >         net->nc->info->stop(net->nc);
> >     }
> > @@ -606,7 +606,7 @@ err_start:
> >         assert(r >= 0);
> >     }
> > 
> > -    vhost_dev_stop(&net->dev, vdev);
> > +    vhost_dev_stop(&net->dev, vdev, false);
> > 
> >     return r;
> > }
> > diff --git a/hw/scsi/vhost-scsi-common.c b/hw/scsi/vhost-scsi-common.c
> > index 767f827e55..18ea5dcfa1 100644
> > --- a/hw/scsi/vhost-scsi-common.c
> > +++ b/hw/scsi/vhost-scsi-common.c
> > @@ -68,7 +68,7 @@ int vhost_scsi_common_start(VHostSCSICommon *vsc)
> >         goto err_guest_notifiers;
> >     }
> > 
> > -    ret = vhost_dev_start(&vsc->dev, vdev);
> > +    ret = vhost_dev_start(&vsc->dev, vdev, true);
> >     if (ret < 0) {
> >         error_report("Error start vhost dev");
> >         goto err_guest_notifiers;
> > @@ -101,7 +101,7 @@ void vhost_scsi_common_stop(VHostSCSICommon *vsc)
> >     VirtioBusClass *k = VIRTIO_BUS_GET_CLASS(qbus);
> >     int ret = 0;
> > 
> > -    vhost_dev_stop(&vsc->dev, vdev);
> > +    vhost_dev_stop(&vsc->dev, vdev, true);
> > 
> >     if (k->set_guest_notifiers) {
> >         ret = k->set_guest_notifiers(qbus->parent, vsc->dev.nvqs, false);
> > diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c
> > index dc4014cdef..d97b179e6f 100644
> > --- a/hw/virtio/vhost-user-fs.c
> > +++ b/hw/virtio/vhost-user-fs.c
> > @@ -76,7 +76,7 @@ static void vuf_start(VirtIODevice *vdev)
> >     }
> > 
> >     fs->vhost_dev.acked_features = vdev->guest_features;
> > -    ret = vhost_dev_start(&fs->vhost_dev, vdev);
> > +    ret = vhost_dev_start(&fs->vhost_dev, vdev, true);
> >     if (ret < 0) {
> >         error_report("Error starting vhost: %d", -ret);
> >         goto err_guest_notifiers;
> > @@ -110,7 +110,7 @@ static void vuf_stop(VirtIODevice *vdev)
> >         return;
> >     }
> > 
> > -    vhost_dev_stop(&fs->vhost_dev, vdev);
> > +    vhost_dev_stop(&fs->vhost_dev, vdev, true);
> > 
> >     ret = k->set_guest_notifiers(qbus->parent, fs->vhost_dev.nvqs, false);
> >     if (ret < 0) {
> > diff --git a/hw/virtio/vhost-user-gpio.c b/hw/virtio/vhost-user-gpio.c
> > index 5851cb3bc9..0b40ebd15a 100644
> > --- a/hw/virtio/vhost-user-gpio.c
> > +++ b/hw/virtio/vhost-user-gpio.c
> > @@ -81,7 +81,7 @@ static int vu_gpio_start(VirtIODevice *vdev)
> >      */
> >     vhost_ack_features(&gpio->vhost_dev, feature_bits, 
> > vdev->guest_features);
> > 
> > -    ret = vhost_dev_start(&gpio->vhost_dev, vdev);
> > +    ret = vhost_dev_start(&gpio->vhost_dev, vdev, false);
> >     if (ret < 0) {
> >         error_report("Error starting vhost-user-gpio: %d", ret);
> >         goto err_guest_notifiers;
> > @@ -139,7 +139,7 @@ static void vu_gpio_stop(VirtIODevice *vdev)
> >         return;
> >     }
> > 
> > -    vhost_dev_stop(vhost_dev, vdev);
> > +    vhost_dev_stop(vhost_dev, vdev, false);
> > 
> >     ret = k->set_guest_notifiers(qbus->parent, vhost_dev->nvqs, false);
> >     if (ret < 0) {
> > diff --git a/hw/virtio/vhost-user-i2c.c b/hw/virtio/vhost-user-i2c.c
> > index 1c9f3d20dc..dc5c828ba6 100644
> > --- a/hw/virtio/vhost-user-i2c.c
> > +++ b/hw/virtio/vhost-user-i2c.c
> > @@ -46,7 +46,7 @@ static void vu_i2c_start(VirtIODevice *vdev)
> > 
> >     i2c->vhost_dev.acked_features = vdev->guest_features;
> > 
> > -    ret = vhost_dev_start(&i2c->vhost_dev, vdev);
> > +    ret = vhost_dev_start(&i2c->vhost_dev, vdev, true);
> >     if (ret < 0) {
> >         error_report("Error starting vhost-user-i2c: %d", -ret);
> >         goto err_guest_notifiers;
> > @@ -80,7 +80,7 @@ static void vu_i2c_stop(VirtIODevice *vdev)
> >         return;
> >     }
> > 
> > -    vhost_dev_stop(&i2c->vhost_dev, vdev);
> > +    vhost_dev_stop(&i2c->vhost_dev, vdev, true);
> > 
> >     ret = k->set_guest_notifiers(qbus->parent, i2c->vhost_dev.nvqs, false);
> >     if (ret < 0) {
> > diff --git a/hw/virtio/vhost-user-rng.c b/hw/virtio/vhost-user-rng.c
> > index f9084cde58..201a39e220 100644
> > --- a/hw/virtio/vhost-user-rng.c
> > +++ b/hw/virtio/vhost-user-rng.c
> > @@ -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) {
> > diff --git a/hw/virtio/vhost-vsock-common.c b/hw/virtio/vhost-vsock-common.c
> > index a67a275de2..d21c72b401 100644
> > --- a/hw/virtio/vhost-vsock-common.c
> > +++ b/hw/virtio/vhost-vsock-common.c
> > @@ -70,7 +70,7 @@ int vhost_vsock_common_start(VirtIODevice *vdev)
> >     }
> > 
> >     vvc->vhost_dev.acked_features = vdev->guest_features;
> > -    ret = vhost_dev_start(&vvc->vhost_dev, vdev);
> > +    ret = vhost_dev_start(&vvc->vhost_dev, vdev, true);
> >     if (ret < 0) {
> >         error_report("Error starting vhost: %d", -ret);
> >         goto err_guest_notifiers;
> > @@ -105,7 +105,7 @@ void vhost_vsock_common_stop(VirtIODevice *vdev)
> >         return;
> >     }
> > 
> > -    vhost_dev_stop(&vvc->vhost_dev, vdev);
> > +    vhost_dev_stop(&vvc->vhost_dev, vdev, true);
> > 
> >     ret = k->set_guest_notifiers(qbus->parent, vvc->vhost_dev.nvqs, false);
> >     if (ret < 0) {
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> > index d1c4c20b8c..7fb008bc9e 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -1777,15 +1777,36 @@ int vhost_dev_get_inflight(struct vhost_dev *dev, 
> > uint16_t queue_size,
> >     return 0;
> > }
> > 
> > +static int vhost_dev_set_vring_enable(struct vhost_dev *hdev, int enable)
> > +{
> > +    if (!hdev->vhost_ops->vhost_set_vring_enable) {
> > +        return 0;
> > +    }
> > +
> > +    /*
> > +     * For vhost-user devices, if VHOST_USER_F_PROTOCOL_FEATURES has not
> > +     * been negotiated, the rings start directly in the enabled state, and
> > +     * .vhost_set_vring_enable callback will fail since
> > +     * VHOST_USER_SET_VRING_ENABLE is not supported.
> > +     */
> > +    if (hdev->vhost_ops->backend_type == VHOST_BACKEND_TYPE_USER &&
> > +        !virtio_has_feature(hdev->backend_features,
> > +                            VHOST_USER_F_PROTOCOL_FEATURES)) {
> > +        return 0;
> > +    }
> > +
> > +    return hdev->vhost_ops->vhost_set_vring_enable(hdev, enable);
> > +}
> > +
> > /* Host notifiers must be enabled at this point. */
> > -int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev)
> > +int vhost_dev_start(struct vhost_dev *hdev, VirtIODevice *vdev, bool 
> > vrings)
> > {
> >     int i, r;
> > 
> >     /* should only be called after backend is connected */
> >     assert(hdev->vhost_ops);
> > 
> > -    trace_vhost_dev_start(hdev, vdev->name);
> > +    trace_vhost_dev_start(hdev, vdev->name, vrings);
> > 
> >     vdev->vhost_started = true;
> >     hdev->started = true;
> > @@ -1830,10 +1851,16 @@ int vhost_dev_start(struct vhost_dev *hdev, 
> > VirtIODevice *vdev)
> >             goto fail_log;
> >         }
> >     }
> > +    if (vrings) {
> > +        r = vhost_dev_set_vring_enable(hdev, true);
> > +        if (r) {
> > +            goto fail_log;
> > +        }
> > +    }
> >     if (hdev->vhost_ops->vhost_dev_start) {
> >         r = hdev->vhost_ops->vhost_dev_start(hdev, true);
> >         if (r) {
> > -            goto fail_log;
> > +            goto fail_start;
> >         }
> >     }
> >     if (vhost_dev_has_iommu(hdev) &&
> > @@ -1848,6 +1875,10 @@ int vhost_dev_start(struct vhost_dev *hdev, 
> > VirtIODevice *vdev)
> >         }
> >     }
> >     return 0;
> > +fail_start:
> > +    if (vrings) {
> > +        vhost_dev_set_vring_enable(hdev, false);
> > +    }
> > fail_log:
> >     vhost_log_put(hdev, false);
> > fail_vq:
> > @@ -1866,18 +1897,21 @@ fail_features:
> > }
> > 
> > /* Host notifiers must be enabled at this point. */
> > -void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev)
> > +void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev, bool 
> > vrings)
> > {
> >     int i;
> > 
> >     /* should only be called after backend is connected */
> >     assert(hdev->vhost_ops);
> > 
> > -    trace_vhost_dev_stop(hdev, vdev->name);
> > +    trace_vhost_dev_stop(hdev, vdev->name, vrings);
> > 
> >     if (hdev->vhost_ops->vhost_dev_start) {
> >         hdev->vhost_ops->vhost_dev_start(hdev, false);
> >     }
> > +    if (vrings) {
> > +        vhost_dev_set_vring_enable(hdev, false);
> > +    }
> >     for (i = 0; i < hdev->nvqs; ++i) {
> >         vhost_virtqueue_stop(hdev,
> >                              vdev,
> > diff --git a/hw/virtio/trace-events b/hw/virtio/trace-events
> > index 820dadc26c..14fc5b9bb2 100644
> > --- a/hw/virtio/trace-events
> > +++ b/hw/virtio/trace-events
> > @@ -9,8 +9,8 @@ vhost_section(const char *name) "%s"
> > vhost_reject_section(const char *name, int d) "%s:%d"
> > vhost_iotlb_miss(void *dev, int step) "%p step %d"
> > vhost_dev_cleanup(void *dev) "%p"
> > -vhost_dev_start(void *dev, const char *name) "%p:%s"
> > -vhost_dev_stop(void *dev, const char *name) "%p:%s"
> > +vhost_dev_start(void *dev, const char *name, bool vrings) "%p:%s vrings:%d"
> > +vhost_dev_stop(void *dev, const char *name, bool vrings) "%p:%s vrings:%d"
> > 
> > 
> > # vhost-user.c
> > -- 
> > 2.38.1
> > 




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