Re: [RFC 09/10] vhost: Route guest->host notification through shadow virtqueue

[Jason Wang <jasowang@redhat.com>]

On 2021/1/30 上午4:54, Eugenio Pérez wrote:
> Shadow virtqueue notifications forwarding is disabled when vhost_dev
> stops.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>   hw/virtio/vhost-shadow-virtqueue.h |   5 ++
>   include/hw/virtio/vhost.h          |   4 +
>   hw/virtio/vhost-shadow-virtqueue.c | 123 +++++++++++++++++++++++++-
>   hw/virtio/vhost.c                  | 135 ++++++++++++++++++++++++++++-
>   4 files changed, 264 insertions(+), 3 deletions(-)
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.h b/hw/virtio/vhost-shadow-virtqueue.h
> index 6cc18d6acb..466f8ae595 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.h
> +++ b/hw/virtio/vhost-shadow-virtqueue.h
> @@ -17,6 +17,11 @@
>   
>   typedef struct VhostShadowVirtqueue VhostShadowVirtqueue;
>   
> +bool vhost_shadow_vq_start_rcu(struct vhost_dev *dev,
> +                               VhostShadowVirtqueue *svq);
> +void vhost_shadow_vq_stop_rcu(struct vhost_dev *dev,
> +                              VhostShadowVirtqueue *svq);
> +
>   VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx);
>   
>   void vhost_shadow_vq_free(VhostShadowVirtqueue *vq);
> diff --git a/include/hw/virtio/vhost.h b/include/hw/virtio/vhost.h
> index 2be782cefd..732a4b2a2b 100644
> --- a/include/hw/virtio/vhost.h
> +++ b/include/hw/virtio/vhost.h
> @@ -55,6 +55,8 @@ struct vhost_iommu {
>       QLIST_ENTRY(vhost_iommu) iommu_next;
>   };
>   
> +typedef struct VhostShadowVirtqueue VhostShadowVirtqueue;
> +
>   typedef struct VhostDevConfigOps {
>       /* Vhost device config space changed callback
>        */
> @@ -83,7 +85,9 @@ struct vhost_dev {
>       uint64_t backend_cap;
>       bool started;
>       bool log_enabled;
> +    bool sw_lm_enabled;
>       uint64_t log_size;
> +    VhostShadowVirtqueue **shadow_vqs;
>       Error *migration_blocker;
>       const VhostOps *vhost_ops;
>       void *opaque;
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
> index c0c967a7c5..908c36c66d 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -8,15 +8,129 @@
>    */
>   
>   #include "hw/virtio/vhost-shadow-virtqueue.h"
> +#include "hw/virtio/vhost.h"
> +#include "hw/virtio/virtio-access.h"
> +
> +#include "standard-headers/linux/vhost_types.h"
> +#include "standard-headers/linux/virtio_ring.h"
>   
>   #include "qemu/error-report.h"
> -#include "qemu/event_notifier.h"
> +#include "qemu/main-loop.h"
>   
>   typedef struct VhostShadowVirtqueue {
>       EventNotifier kick_notifier;
>       EventNotifier call_notifier;
> +    const struct vhost_virtqueue *hvq;
> +    VirtIODevice *vdev;
> +    VirtQueue *vq;
>   } VhostShadowVirtqueue;


So instead of doing things at virtio level, how about do the shadow 
stuffs at vhost level?

It works like:

virtio -> [shadow vhost backend] -> vhost backend

Then the QMP is used to plug the shadow vhost backend in the middle or not.

It looks kind of easier since we don't need to deal with virtqueue 
handlers etc.. Instead, we just need to deal with eventfd stuffs:

When shadow vhost mode is enabled, we just intercept the host_notifiers 
and guest_notifiers. When it was disabled, we just pass the host/guest 
notifiers to the real vhost backends?

Thanks


>   
> +static uint16_t vhost_shadow_vring_used_flags(VhostShadowVirtqueue *svq)
> +{
> +    const struct vring_used *used = svq->hvq->used;
> +    return virtio_tswap16(svq->vdev, used->flags);
> +}
> +
> +static bool vhost_shadow_vring_should_kick(VhostShadowVirtqueue *vq)
> +{
> +    return !(vhost_shadow_vring_used_flags(vq) & VRING_USED_F_NO_NOTIFY);
> +}
> +
> +static void vhost_shadow_vring_kick(VhostShadowVirtqueue *vq)
> +{
> +    if (vhost_shadow_vring_should_kick(vq)) {
> +        event_notifier_set(&vq->kick_notifier);
> +    }
> +}
> +
> +static void handle_shadow_vq(VirtIODevice *vdev, VirtQueue *vq)
> +{
> +    struct vhost_dev *hdev = vhost_dev_from_virtio(vdev);
> +    uint16_t idx = virtio_get_queue_index(vq);
> +
> +    VhostShadowVirtqueue *svq = hdev->shadow_vqs[idx];
> +
> +    vhost_shadow_vring_kick(svq);
> +}
> +
> +/*
> + * Start shadow virtqueue operation.
> + * @dev vhost device
> + * @svq Shadow Virtqueue
> + *
> + * Run in RCU context
> + */
> +bool vhost_shadow_vq_start_rcu(struct vhost_dev *dev,
> +                               VhostShadowVirtqueue *svq)
> +{
> +    const VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(dev->vdev);
> +    EventNotifier *vq_host_notifier = virtio_queue_get_host_notifier(svq->vq);
> +    unsigned idx = virtio_queue_get_idx(svq->vdev, svq->vq);
> +    struct vhost_vring_file kick_file = {
> +        .index = idx,
> +        .fd = event_notifier_get_fd(&svq->kick_notifier),
> +    };
> +    int r;
> +    bool ok;
> +
> +    /* Check that notifications are still going directly to vhost dev */
> +    assert(virtio_queue_host_notifier_status(svq->vq));
> +
> +    ok = k->set_vq_handler(dev->vdev, idx, handle_shadow_vq);
> +    if (!ok) {
> +        error_report("Couldn't set the vq handler");
> +        goto err_set_kick_handler;
> +    }
> +
> +    r = dev->vhost_ops->vhost_set_vring_kick(dev, &kick_file);
> +    if (r != 0) {
> +        error_report("Couldn't set kick fd: %s", strerror(errno));
> +        goto err_set_vring_kick;
> +    }
> +
> +    event_notifier_set_handler(vq_host_notifier,
> +                               virtio_queue_host_notifier_read);
> +    virtio_queue_set_host_notifier_enabled(svq->vq, false);
> +    virtio_queue_host_notifier_read(vq_host_notifier);
> +
> +    return true;
> +
> +err_set_vring_kick:
> +    k->set_vq_handler(dev->vdev, idx, NULL);
> +
> +err_set_kick_handler:
> +    return false;
> +}
> +
> +/*
> + * Stop shadow virtqueue operation.
> + * @dev vhost device
> + * @svq Shadow Virtqueue
> + *
> + * Run in RCU context
> + */
> +void vhost_shadow_vq_stop_rcu(struct vhost_dev *dev,
> +                              VhostShadowVirtqueue *svq)
> +{
> +    const VirtioDeviceClass *k = VIRTIO_DEVICE_GET_CLASS(svq->vdev);
> +    unsigned idx = virtio_queue_get_idx(svq->vdev, svq->vq);
> +    EventNotifier *vq_host_notifier = virtio_queue_get_host_notifier(svq->vq);
> +    struct vhost_vring_file kick_file = {
> +        .index = idx,
> +        .fd = event_notifier_get_fd(vq_host_notifier),
> +    };
> +    int r;
> +
> +    /* Restore vhost kick */
> +    r = dev->vhost_ops->vhost_set_vring_kick(dev, &kick_file);
> +    /* Cannot do a lot of things */
> +    assert(r == 0);
> +
> +    event_notifier_set_handler(vq_host_notifier, NULL);
> +    virtio_queue_set_host_notifier_enabled(svq->vq, true);
> +    k->set_vq_handler(svq->vdev, idx, NULL);
> +}
> +
>   /*
>    * Creates vhost shadow virtqueue, and instruct vhost device to use the shadow
>    * methods and file descriptors.
> @@ -24,8 +138,13 @@ typedef struct VhostShadowVirtqueue {
>   VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx)
>   {
>       g_autofree VhostShadowVirtqueue *svq = g_new0(VhostShadowVirtqueue, 1);
> +    int vq_idx = dev->vhost_ops->vhost_get_vq_index(dev, dev->vq_index + idx);
>       int r;
>   
> +    svq->vq = virtio_get_queue(dev->vdev, vq_idx);
> +    svq->hvq = &dev->vqs[idx];
> +    svq->vdev = dev->vdev;
> +
>       r = event_notifier_init(&svq->kick_notifier, 0);
>       if (r != 0) {
>           error_report("Couldn't create kick event notifier: %s",
> @@ -40,7 +159,7 @@ VhostShadowVirtqueue *vhost_shadow_vq_new(struct vhost_dev *dev, int idx)
>           goto err_init_call_notifier;
>       }
>   
> -    return svq;
> +    return g_steal_pointer(&svq);
>   
>   err_init_call_notifier:
>       event_notifier_cleanup(&svq->kick_notifier);
> diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> index 42836e45f3..bde688f278 100644
> --- a/hw/virtio/vhost.c
> +++ b/hw/virtio/vhost.c
> @@ -25,6 +25,7 @@
>   #include "exec/address-spaces.h"
>   #include "hw/virtio/virtio-bus.h"
>   #include "hw/virtio/virtio-access.h"
> +#include "hw/virtio/vhost-shadow-virtqueue.h"
>   #include "migration/blocker.h"
>   #include "migration/qemu-file-types.h"
>   #include "sysemu/dma.h"
> @@ -945,6 +946,82 @@ static void vhost_log_global_stop(MemoryListener *listener)
>       }
>   }
>   
> +static int vhost_sw_live_migration_stop(struct vhost_dev *dev)
> +{
> +    int idx;
> +
> +    WITH_RCU_READ_LOCK_GUARD() {
> +        dev->sw_lm_enabled = false;
> +
> +        for (idx = 0; idx < dev->nvqs; ++idx) {
> +            vhost_shadow_vq_stop_rcu(dev, dev->shadow_vqs[idx]);
> +        }
> +    }
> +
> +    for (idx = 0; idx < dev->nvqs; ++idx) {
> +        vhost_shadow_vq_free(dev->shadow_vqs[idx]);
> +    }
> +
> +    g_free(dev->shadow_vqs);
> +    dev->shadow_vqs = NULL;
> +    return 0;
> +}
> +
> +static int vhost_sw_live_migration_start(struct vhost_dev *dev)
> +{
> +    int idx;
> +
> +    dev->shadow_vqs = g_new0(VhostShadowVirtqueue *, dev->nvqs);
> +    for (idx = 0; idx < dev->nvqs; ++idx) {
> +        dev->shadow_vqs[idx] = vhost_shadow_vq_new(dev, idx);
> +        if (unlikely(dev->shadow_vqs[idx] == NULL)) {
> +            goto err;
> +        }
> +    }
> +
> +    WITH_RCU_READ_LOCK_GUARD() {
> +        for (idx = 0; idx < dev->nvqs; ++idx) {
> +            int stop_idx = idx;
> +            bool ok = vhost_shadow_vq_start_rcu(dev,
> +                                                dev->shadow_vqs[idx]);
> +
> +            if (!ok) {
> +                while (--stop_idx >= 0) {
> +                    vhost_shadow_vq_stop_rcu(dev, dev->shadow_vqs[stop_idx]);
> +                }
> +
> +                goto err;
> +            }
> +        }
> +    }
> +
> +    dev->sw_lm_enabled = true;
> +    return 0;
> +
> +err:
> +    for (; idx >= 0; --idx) {
> +        vhost_shadow_vq_free(dev->shadow_vqs[idx]);
> +    }
> +    g_free(dev->shadow_vqs[idx]);
> +
> +    return -1;
> +}
> +
> +static int vhost_sw_live_migration_enable(struct vhost_dev *dev,
> +                                          bool enable_lm)
> +{
> +    int r;
> +
> +    if (enable_lm == dev->sw_lm_enabled) {
> +        return 0;
> +    }
> +
> +    r = enable_lm ? vhost_sw_live_migration_start(dev)
> +                  : vhost_sw_live_migration_stop(dev);
> +
> +    return r;
> +}
> +
>   static void vhost_log_start(MemoryListener *listener,
>                               MemoryRegionSection *section,
>                               int old, int new)
> @@ -1389,6 +1466,7 @@ int vhost_dev_init(struct vhost_dev *hdev, void *opaque,
>       hdev->log = NULL;
>       hdev->log_size = 0;
>       hdev->log_enabled = false;
> +    hdev->sw_lm_enabled = false;
>       hdev->started = false;
>       memory_listener_register(&hdev->memory_listener, &address_space_memory);
>       QLIST_INSERT_HEAD(&vhost_devices, hdev, entry);
> @@ -1816,6 +1894,11 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev)
>           hdev->vhost_ops->vhost_dev_start(hdev, false);
>       }
>       for (i = 0; i < hdev->nvqs; ++i) {
> +        if (hdev->sw_lm_enabled) {
> +            vhost_shadow_vq_stop_rcu(hdev, hdev->shadow_vqs[i]);
> +            vhost_shadow_vq_free(hdev->shadow_vqs[i]);
> +        }
> +
>           vhost_virtqueue_stop(hdev,
>                                vdev,
>                                hdev->vqs + i,
> @@ -1829,6 +1912,8 @@ void vhost_dev_stop(struct vhost_dev *hdev, VirtIODevice *vdev)
>           memory_listener_unregister(&hdev->iommu_listener);
>       }
>       vhost_log_put(hdev, true);
> +    g_free(hdev->shadow_vqs);
> +    hdev->sw_lm_enabled = false;
>       hdev->started = false;
>       hdev->vdev = NULL;
>   }
> @@ -1845,5 +1930,53 @@ int vhost_net_set_backend(struct vhost_dev *hdev,
>   
>   void qmp_x_vhost_enable_shadow_vq(const char *name, bool enable, Error **errp)
>   {
> -    error_setg(errp, "Shadow virtqueue still not implemented.");
> +    struct vhost_dev *hdev;
> +    const char *err_cause = NULL;
> +    const VirtioDeviceClass *k;
> +    int r;
> +    ErrorClass err_class = ERROR_CLASS_GENERIC_ERROR;
> +
> +    QLIST_FOREACH(hdev, &vhost_devices, entry) {
> +        if (hdev->vdev && 0 == strcmp(hdev->vdev->name, name)) {
> +            break;
> +        }
> +    }
> +
> +    if (!hdev) {
> +        err_class = ERROR_CLASS_DEVICE_NOT_FOUND;
> +        err_cause = "Device not found";
> +        goto err;
> +    }
> +
> +    if (!hdev->started) {
> +        err_cause = "Device is not started";
> +        goto err;
> +    }
> +
> +    if (hdev->acked_features & BIT_ULL(VIRTIO_F_RING_PACKED)) {
> +        err_cause = "Use packed vq";
> +        goto err;
> +    }
> +
> +    if (vhost_dev_has_iommu(hdev)) {
> +        err_cause = "Device use IOMMU";
> +        goto err;
> +    }
> +
> +    k = VIRTIO_DEVICE_GET_CLASS(hdev->vdev);
> +    if (!k->set_vq_handler) {
> +        err_cause = "Virtio device type does not support reset of vq handler";
> +        goto err;
> +    }
> +
> +    r = vhost_sw_live_migration_enable(hdev, enable);
> +    if (unlikely(r)) {
> +        err_cause = "Error enabling (see monitor)";
> +    }
> +
> +err:
> +    if (err_cause) {
> +        error_set(errp, err_class,
> +                  "Can't enable shadow vq on %s: %s", name, err_cause);
> +    }
>   }

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