On Wed, May 27, 2020 at 04:28:41PM +0200, Marc-André Lureau wrote: > Hi Stefan > > On Fri, May 22, 2020 at 7:18 PM Stefan Hajnoczi wrote: > > > > Many vhost devices in QEMU currently do not involve the device backend > > in feature negotiation. This seems fine at first glance for device types > > without their own feature bits (virtio-net has many but other device > > types have none). > > > > This overlooks the fact that QEMU's virtqueue implementation and the > > device backend's implementation may support different features. QEMU > > must not report features to the guest that the the device backend > > doesn't support. > > > > For example, QEMU supports VIRTIO 1.1 packed virtqueues while many > > existing vhost device backends do not. When the user sets packed=on the > > device backend breaks. This should have been handled gracefully by > > feature negotiation instead. > > > > Introduce vhost_get_default_features() and update all vhost devices in > > QEMU to involve the device backend in feature negotiation. > > > > This patch fixes the following error: > > > > $ x86_64-softmmu/qemu-system-x86_64 \ > > -drive if=virtio,file=test.img,format=raw \ > > -chardev socket,path=/tmp/vhost-user-blk.sock,id=char0 \ > > -device vhost-user-blk-pci,chardev=char0,packed=on \ > > -object memory-backend-memfd,size=1G,share=on,id=ram0 \ > > -M accel=kvm,memory-backend=ram0 > > qemu-system-x86_64: Failed to set msg fds. > > qemu-system-x86_64: vhost VQ 0 ring restore failed: -1: Success (0) > > > > The vhost-user-blk backend failed as follows: > > > > $ ./vhost-user-blk --socket-path=/tmp/vhost-user-blk.sock -b test2.img > > vu_panic: virtio: zero sized buffers are not allowed > > virtio-blk request missing headers > > > > Signed-off-by: Stefan Hajnoczi > > --- > > include/hw/virtio/vhost.h | 1 + > > include/hw/virtio/virtio-gpu.h | 2 ++ > > include/sysemu/cryptodev-vhost.h | 11 +++++++++++ > > backends/cryptodev-vhost.c | 19 +++++++++++++++++++ > > hw/display/vhost-user-gpu.c | 17 +++++++++++++++++ > > hw/display/virtio-gpu-base.c | 2 +- > > hw/input/vhost-user-input.c | 9 +++++++++ > > hw/virtio/vhost-user-fs.c | 5 +++-- > > hw/virtio/vhost-vsock.c | 5 +++-- > > hw/virtio/vhost.c | 22 ++++++++++++++++++++++ > > hw/virtio/virtio-crypto.c | 3 ++- > > 11 files changed, 90 insertions(+), 6 deletions(-) > > > > diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h > > index 085450c6f8..d2e54dd4a8 100644 > > --- a/include/hw/virtio/vhost.h > > +++ b/include/hw/virtio/vhost.h > > @@ -112,6 +112,7 @@ void vhost_virtqueue_mask(struct vhost_dev *hdev, VirtIODevice *vdev, int n, > > bool mask); > > uint64_t vhost_get_features(struct vhost_dev *hdev, const int *feature_bits, > > uint64_t features); > > +uint64_t vhost_get_default_features(struct vhost_dev *hdev, uint64_t features); > > void vhost_ack_features(struct vhost_dev *hdev, const int *feature_bits, > > uint64_t features); > > bool vhost_has_free_slot(void); > > diff --git a/include/hw/virtio/virtio-gpu.h b/include/hw/virtio/virtio-gpu.h > > index 6dd57f2025..41d270d80e 100644 > > --- a/include/hw/virtio/virtio-gpu.h > > +++ b/include/hw/virtio/virtio-gpu.h > > @@ -192,6 +192,8 @@ bool virtio_gpu_base_device_realize(DeviceState *qdev, > > void virtio_gpu_base_reset(VirtIOGPUBase *g); > > void virtio_gpu_base_fill_display_info(VirtIOGPUBase *g, > > struct virtio_gpu_resp_display_info *dpy_info); > > +uint64_t virtio_gpu_base_get_features(VirtIODevice *vdev, uint64_t features, > > + Error **errp); > > > > /* virtio-gpu.c */ > > void virtio_gpu_ctrl_response(VirtIOGPU *g, > > diff --git a/include/sysemu/cryptodev-vhost.h b/include/sysemu/cryptodev-vhost.h > > index f42824fbde..e629446bfb 100644 > > --- a/include/sysemu/cryptodev-vhost.h > > +++ b/include/sysemu/cryptodev-vhost.h > > @@ -122,6 +122,17 @@ int cryptodev_vhost_start(VirtIODevice *dev, int total_queues); > > */ > > void cryptodev_vhost_stop(VirtIODevice *dev, int total_queues); > > > > +/** > > + * cryptodev_vhost_get_features: > > + * @dev: the virtio crypto object > > + * @requested_features: the features being offered > > + * > > + * Returns: the requested features bits that are supported by the vhost device, > > + * or the original request feature bits if vhost is disabled > > + * > > + */ > > +uint64_t cryptodev_vhost_get_features(VirtIODevice *dev, uint64_t features); > > + > > /** > > * cryptodev_vhost_virtqueue_mask: > > * @dev: the virtio crypto object > > diff --git a/backends/cryptodev-vhost.c b/backends/cryptodev-vhost.c > > index 8337c9a495..5f5a4fda7b 100644 > > --- a/backends/cryptodev-vhost.c > > +++ b/backends/cryptodev-vhost.c > > @@ -266,6 +266,20 @@ void cryptodev_vhost_stop(VirtIODevice *dev, int total_queues) > > assert(r >= 0); > > } > > > > +uint64_t cryptodev_vhost_get_features(VirtIODevice *dev, uint64_t features) > > +{ > > + VirtIOCrypto *vcrypto = VIRTIO_CRYPTO(dev); > > + CryptoDevBackend *b = vcrypto->cryptodev; > > + CryptoDevBackendClient *cc = b->conf.peers.ccs[0]; > > + CryptoDevBackendVhost *vhost_crypto = cryptodev_get_vhost(cc, b, 0); > > + > > + if (!vhost_crypto) { > > + return features; /* vhost disabled */ > > + } > > + > > + return vhost_get_default_features(&vhost_crypto->dev, features); > > +} > > + > > void cryptodev_vhost_virtqueue_mask(VirtIODevice *dev, > > int queue, > > int idx, bool mask) > > @@ -333,6 +347,11 @@ void cryptodev_vhost_stop(VirtIODevice *dev, int total_queues) > > { > > } > > > > +uint64_t cryptodev_vhost_get_features(VirtIODevice *dev, uint64_t features) > > +{ > > + return features; > > +} > > + > > void cryptodev_vhost_virtqueue_mask(VirtIODevice *dev, > > int queue, > > int idx, bool mask) > > diff --git a/hw/display/vhost-user-gpu.c b/hw/display/vhost-user-gpu.c > > index 4cdaee1bde..e483df2a9e 100644 > > --- a/hw/display/vhost-user-gpu.c > > +++ b/hw/display/vhost-user-gpu.c > > @@ -466,6 +466,22 @@ vhost_user_gpu_set_config(VirtIODevice *vdev, > > } > > } > > > > +static uint64_t > > +vhost_user_gpu_get_features(VirtIODevice *vdev, uint64_t features, > > + Error **errp) > > +{ > > + VhostUserGPU *g = VHOST_USER_GPU(vdev); > > + Error *local_err = NULL; > > + > > + features = virtio_gpu_base_get_features(vdev, features, &local_err); > > + if (local_err) { > > + error_propagate(errp, local_err); > > + return 0; > > + } > > + > > + return vhost_get_default_features(&g->vhost->dev, features); > > +} > > + > > static void > > vhost_user_gpu_set_status(VirtIODevice *vdev, uint8_t val) > > { > > @@ -582,6 +598,7 @@ vhost_user_gpu_class_init(ObjectClass *klass, void *data) > > > > vdc->realize = vhost_user_gpu_device_realize; > > vdc->reset = vhost_user_gpu_reset; > > + vdc->get_features = vhost_user_gpu_get_features; > > vdc->set_status = vhost_user_gpu_set_status; > > vdc->guest_notifier_mask = vhost_user_gpu_guest_notifier_mask; > > vdc->guest_notifier_pending = vhost_user_gpu_guest_notifier_pending; > > diff --git a/hw/display/virtio-gpu-base.c b/hw/display/virtio-gpu-base.c > > index c159351be3..05d1ff2db2 100644 > > --- a/hw/display/virtio-gpu-base.c > > +++ b/hw/display/virtio-gpu-base.c > > @@ -176,7 +176,7 @@ virtio_gpu_base_device_realize(DeviceState *qdev, > > return true; > > } > > > > -static uint64_t > > +uint64_t > > virtio_gpu_base_get_features(VirtIODevice *vdev, uint64_t features, > > Error **errp) > > { > > diff --git a/hw/input/vhost-user-input.c b/hw/input/vhost-user-input.c > > index 63984a8ba7..1371fb32cc 100644 > > --- a/hw/input/vhost-user-input.c > > +++ b/hw/input/vhost-user-input.c > > @@ -45,6 +45,14 @@ static void vhost_input_change_active(VirtIOInput *vinput) > > } > > } > > > > +static uint64_t vhost_input_get_features(VirtIODevice *vdev, uint64_t features, > > + Error **errp) > > +{ > > + VHostUserInput *vhi = VHOST_USER_INPUT(vdev); > > + > > + return vhost_get_default_features(&vhi->vhost->dev, features); > > +} > > + > > static void vhost_input_get_config(VirtIODevice *vdev, uint8_t *config_data) > > { > > VirtIOInput *vinput = VIRTIO_INPUT(vdev); > > @@ -89,6 +97,7 @@ static void vhost_input_class_init(ObjectClass *klass, void *data) > > DeviceClass *dc = DEVICE_CLASS(klass); > > > > dc->vmsd = &vmstate_vhost_input; > > + vdc->get_features = vhost_input_get_features; > > vdc->get_config = vhost_input_get_config; > > vdc->set_config = vhost_input_set_config; > > vic->realize = vhost_input_realize; > > diff --git a/hw/virtio/vhost-user-fs.c b/hw/virtio/vhost-user-fs.c > > index 1bc5d03a00..56015ca3d4 100644 > > --- a/hw/virtio/vhost-user-fs.c > > +++ b/hw/virtio/vhost-user-fs.c > > @@ -130,8 +130,9 @@ static uint64_t vuf_get_features(VirtIODevice *vdev, > > uint64_t requested_features, > > Error **errp) > > { > > - /* No feature bits used yet */ > > - return requested_features; > > + VHostUserFS *fs = VHOST_USER_FS(vdev); > > + > > + return vhost_get_default_features(&fs->vhost_dev, requested_features); > > } > > > > static void vuf_handle_output(VirtIODevice *vdev, VirtQueue *vq) > > diff --git a/hw/virtio/vhost-vsock.c b/hw/virtio/vhost-vsock.c > > index 4a228f5168..7276587be6 100644 > > --- a/hw/virtio/vhost-vsock.c > > +++ b/hw/virtio/vhost-vsock.c > > @@ -180,8 +180,9 @@ static uint64_t vhost_vsock_get_features(VirtIODevice *vdev, > > uint64_t requested_features, > > Error **errp) > > { > > - /* No feature bits used yet */ > > - return requested_features; > > + VHostVSock *vsock = VHOST_VSOCK(vdev); > > + > > + return vhost_get_default_features(&vsock->vhost_dev, requested_features); > > } > > > > static void vhost_vsock_handle_output(VirtIODevice *vdev, VirtQueue *vq) > > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c > > index aff98a0ede..f8a144dcd0 100644 > > --- a/hw/virtio/vhost.c > > +++ b/hw/virtio/vhost.c > > @@ -48,6 +48,23 @@ static unsigned int used_memslots; > > static QLIST_HEAD(, vhost_dev) vhost_devices = > > QLIST_HEAD_INITIALIZER(vhost_devices); > > > > +/* > > + * Feature bits that device backends must explicitly report. Feature bits not > > + * listed here maybe set by QEMU without checking with the device backend. > > + * Ideally all feature bits would be listed here but existing vhost device > > + * implementations do not explicitly report bits like VIRTIO_F_VERSION_1, so we > > + * can only assume they are supported. > > + * > > + * New feature bits added to the VIRTIO spec should usually be included here > > + * so that existing vhost device backends that do not support them yet continue > > + * to work. > > + */ > > +static const int vhost_default_feature_bits[] = { > > + VIRTIO_F_IOMMU_PLATFORM, > > + VIRTIO_F_RING_PACKED, > > So effectively, we don't care about backend features except for those > 2 bits, and an extra F_LOG_ALL check in vhost.c, right? > > It's not entirely clear to me how the feature flags of device and > backend should combine tbh. I've always found this confusing too. Maybe a vhost-user spec clarification would help improve the situation at least for future vhost-user backend implementors. libvhost-user only advertises VHOST_F_LOG_ALL and VHOST_USER_F_PROTOCOL_FEATURES. Everything else is left up to the device backend implementation. This is a problem because libvhost-user handles virtqueues and needs to be aware of VIRTIO_RING_F_EVENT_IDX, etc. I'll send a separate patch to advertise the necessary feature bits in libvhost-user. QEMU calculates the VIRTIO device's feature bit masks as follows: 1. -device vhost-foo initializes the device features with whatever QEMU supports. Either the QEMU vhost-foo code itself sets features or the user overrides them on the command-line. 2. Some vhost devices in QEMU call vhost_get_features() to mask out features missing from the VHOST_USER_GET_FEATURES response. This is how the vhost-user backend participates in feature negotiation. This patch series changes moves us one step in the direction of always involving the vhost-user backend in feature negotiation. It's only a step because to do so fully would break existing vhost-user backends that don't advertise features properly :(. Stefan