Re: [PATCH v2 07/13] vdpa: add vdpa net migration state notifier

[Eugenio Perez Martin]

On Mon, Feb 13, 2023 at 7:51 AM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
>
> On 2/8/2023 1:42 AM, Eugenio Pérez wrote:
> > This allows net to restart the device backend to configure SVQ on it.
> >
> > Ideally, these changes should not be net specific. However, the vdpa net
> > backend is the one with enough knowledge to configure everything because
> > of some reasons:
> > * Queues might need to be shadowed or not depending on its kind (control
> >    vs data).
> > * Queues need to share the same map translations (iova tree).
> >
> > Because of that it is cleaner to restart the whole net backend and
> > configure again as expected, similar to how vhost-kernel moves between
> > userspace and passthrough.
> >
> > If more kinds of devices need dynamic switching to SVQ we can create a
> > callback struct like VhostOps and move most of the code there.
> > VhostOps cannot be reused since all vdpa backend share them, and to
> > personalize just for networking would be too heavy.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > ---
> > v3:
> > * Add TODO to use the resume operation in the future.
> > * Use migration_in_setup and migration_has_failed instead of a
> >    complicated switch case.
> > ---
> >   net/vhost-vdpa.c | 76 ++++++++++++++++++++++++++++++++++++++++++++++++
> >   1 file changed, 76 insertions(+)
> >
> > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > index dd686b4514..bca13f97fd 100644
> > --- a/net/vhost-vdpa.c
> > +++ b/net/vhost-vdpa.c
> > @@ -26,12 +26,14 @@
> >   #include <err.h>
> >   #include "standard-headers/linux/virtio_net.h"
> >   #include "monitor/monitor.h"
> > +#include "migration/misc.h"
> >   #include "hw/virtio/vhost.h"
> >
> >   /* Todo:need to add the multiqueue support here */
> >   typedef struct VhostVDPAState {
> >       NetClientState nc;
> >       struct vhost_vdpa vhost_vdpa;
> > +    Notifier migration_state;
> >       VHostNetState *vhost_net;
> >
> >       /* Control commands shadow buffers */
> > @@ -241,10 +243,79 @@ static VhostVDPAState 
> > *vhost_vdpa_net_first_nc_vdpa(VhostVDPAState *s)
> >       return DO_UPCAST(VhostVDPAState, nc, nc0);
> >   }
> >
> > +static void vhost_vdpa_net_log_global_enable(VhostVDPAState *s, bool 
> > enable)
> > +{
> > +    struct vhost_vdpa *v = &s->vhost_vdpa;
> > +    VirtIONet *n;
> > +    VirtIODevice *vdev;
> > +    int data_queue_pairs, cvq, r;
> > +    NetClientState *peer;
> > +
> > +    /* We are only called on the first data vqs and only if x-svq is not 
> > set */
> > +    if (s->vhost_vdpa.shadow_vqs_enabled == enable) {
> > +        return;
> > +    }
> > +
> > +    vdev = v->dev->vdev;
> > +    n = VIRTIO_NET(vdev);
> > +    if (!n->vhost_started) {
> > +        return;
> What if vhost gets started after migration is started, will svq still be
> (dynamically) enabled during vhost_dev_start()? I don't see relevant
> code to deal with it?
>

Good catch. v->shadow_vqs_enabled must change even if
!n->vhost_started. That should be the only code needed.

Also, migration listener must be registered from qemu startup, not on
device start.

> > +    }
> > +
> > +    data_queue_pairs = n->multiqueue ? n->max_queue_pairs : 1;
> > +    cvq = virtio_vdev_has_feature(vdev, VIRTIO_NET_F_CTRL_VQ) ?
> > +                                  n->max_ncs - n->max_queue_pairs : 0;
> > +    /*
> > +     * TODO: vhost_net_stop does suspend, get_base and reset. We can be 
> > smarter
> > +     * in the future and resume the device if read-only operations between
> > +     * suspend and reset goes wrong.
> > +     */
> > +    vhost_net_stop(vdev, n->nic->ncs, data_queue_pairs, cvq);
> > +
> > +    peer = s->nc.peer;
> > +    for (int i = 0; i < data_queue_pairs + cvq; i++) {
> > +        VhostVDPAState *vdpa_state;
> > +        NetClientState *nc;
> > +
> > +        if (i < data_queue_pairs) {
> > +            nc = qemu_get_peer(peer, i);
> > +        } else {
> > +            nc = qemu_get_peer(peer, n->max_queue_pairs);
> > +        }
> > +
> > +        vdpa_state = DO_UPCAST(VhostVDPAState, nc, nc);
> > +        vdpa_state->vhost_vdpa.shadow_data = enable;
> Don't get why shadow_data is set on cvq's vhost_vdpa? This may result in
> address space collision: data vq's iova getting improperly allocated on
> cvq's address space in vhost_vdpa_listener_region_{add,del}(). Noted
> currently there's an issue where guest VM's memory listener registration
> is always hooked to the last vq, which could be on the cvq in a
> different iova address space VHOST_VDPA_NET_CVQ_ASID.
>

Let me answer in reverse. guest VM's memory listener registration is
effectively always hooked to the last vq, that's why shadow_data is
needed.

In the past it was enough with v->shadow_vqs_enabled. However, since
the introduction of ASID support & CVQ tracking through it, The
listener (hooked at CVQ) needs to know if it should use iova tree or
not. That's why a separated variable shadow_data is needed.

That way, it may happen that cvq vhost_vdpa->shadow_vqs_enabled = true
but cvq vhost_vdpa->shadow_vqs_enabledshadow_data = false.

Is that clearer?

Thanks!

> Thanks,
> -Siwei
>
> > +
> > +        if (i < data_queue_pairs) {
> > +            /* Do not override CVQ shadow_vqs_enabled */
> > +            vdpa_state->vhost_vdpa.shadow_vqs_enabled = enable;
> > +        }
> > +    }
> > +
> > +    r = vhost_net_start(vdev, n->nic->ncs, data_queue_pairs, cvq);
> > +    if (unlikely(r < 0)) {
> > +        error_report("unable to start vhost net: %s(%d)", g_strerror(-r), 
> > -r);
> > +    }
> > +}
> > +
> > +static void vdpa_net_migration_state_notifier(Notifier *notifier, void 
> > *data)
> > +{
> > +    MigrationState *migration = data;
> > +    VhostVDPAState *s = container_of(notifier, VhostVDPAState,
> > +                                     migration_state);
> > +
> > +    if (migration_in_setup(migration)) {
> > +        vhost_vdpa_net_log_global_enable(s, true);
> > +    } else if (migration_has_failed(migration)) {
> > +        vhost_vdpa_net_log_global_enable(s, false);
> > +    }
> > +}
> > +
> >   static void vhost_vdpa_net_data_start_first(VhostVDPAState *s)
> >   {
> >       struct vhost_vdpa *v = &s->vhost_vdpa;
> >
> > +    add_migration_state_change_notifier(&s->migration_state);
> >       if (v->shadow_vqs_enabled) {
> >           v->iova_tree = vhost_iova_tree_new(v->iova_range.first,
> >                                              v->iova_range.last);
> > @@ -278,6 +349,10 @@ static void vhost_vdpa_net_client_stop(NetClientState 
> > *nc)
> >
> >       assert(nc->info->type == NET_CLIENT_DRIVER_VHOST_VDPA);
> >
> > +    if (s->vhost_vdpa.index == 0) {
> > +        remove_migration_state_change_notifier(&s->migration_state);
> > +    }
> > +
> >       dev = s->vhost_vdpa.dev;
> >       if (dev->vq_index + dev->nvqs == dev->vq_index_end) {
> >           g_clear_pointer(&s->vhost_vdpa.iova_tree, vhost_iova_tree_delete);
> > @@ -741,6 +816,7 @@ static NetClientState 
> > *net_vhost_vdpa_init(NetClientState *peer,
> >       s->vhost_vdpa.device_fd = vdpa_device_fd;
> >       s->vhost_vdpa.index = queue_pair_index;
> >       s->always_svq = svq;
> > +    s->migration_state.notify = vdpa_net_migration_state_notifier;
> >       s->vhost_vdpa.shadow_vqs_enabled = svq;
> >       s->vhost_vdpa.iova_range = iova_range;
> >       s->vhost_vdpa.shadow_data = svq;
>