Re: [RFC v2 05/13] vdpa net: add migration blocker if cannot migrate cvq

[Eugenio Perez Martin]

On Fri, Jan 13, 2023 at 5:25 AM Jason Wang <jasowang@redhat.com> wrote:
>
>
> 在 2023/1/13 01:24, Eugenio Pérez 写道:
> > A vdpa net device must initialize with SVQ in order to be migratable,
> > and initialization code verifies conditions.  If the device is not
> > initialized with the x-svq parameter, it will not expose _F_LOG so vhost
> > sybsystem will block VM migration from its initialization.
> >
> > Next patches change this. Net data VQs will be shadowed only at
> > migration time and vdpa net devices need to expose _F_LOG as long as it
> > can go to SVQ.
> >
> > Since we don't know that at initialization time but at start, add an
> > independent blocker at CVQ.
> >
> > Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> > ---
> >   net/vhost-vdpa.c | 35 +++++++++++++++++++++++++++++------
> >   1 file changed, 29 insertions(+), 6 deletions(-)
> >
> > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > index 631424d9c4..2ca93e850a 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/blocker.h"
> >   #include "hw/virtio/vhost.h"
> >
> >   /* Todo:need to add the multiqueue support here */
> >   typedef struct VhostVDPAState {
> >       NetClientState nc;
> >       struct vhost_vdpa vhost_vdpa;
> > +    Error *migration_blocker;
>
>
> Any reason we can't use the mivration_blocker in vhost_dev structure?
>
> I believe we don't need to wait until start to know we can't migrate.
>

Device migratability also depends on features that the guest acks.

For example, if the device does not support ASID it can be migrated as
long as _F_CVQ is not acked.

Thanks!

>
> Thanks
>
>
> >       VHostNetState *vhost_net;
> >
> >       /* Control commands shadow buffers */
> > @@ -433,9 +435,15 @@ static int vhost_vdpa_net_cvq_start(NetClientState *nc)
> >               g_strerror(errno), errno);
> >           return -1;
> >       }
> > -    if (!(backend_features & BIT_ULL(VHOST_BACKEND_F_IOTLB_ASID)) ||
> > -        !vhost_vdpa_net_valid_svq_features(v->dev->features, NULL)) {
> > -        return 0;
> > +    if (!(backend_features & BIT_ULL(VHOST_BACKEND_F_IOTLB_ASID))) {
> > +        error_setg(&s->migration_blocker,
> > +                   "vdpa device %s does not support ASID",
> > +                   nc->name);
> > +        goto out;
> > +    }
> > +    if (!vhost_vdpa_net_valid_svq_features(v->dev->features,
> > +                                           &s->migration_blocker)) {
> > +        goto out;
> >       }
> >
> >       /*
> > @@ -455,7 +463,10 @@ static int vhost_vdpa_net_cvq_start(NetClientState *nc)
> >           }
> >
> >           if (group == cvq_group) {
> > -            return 0;
> > +            error_setg(&s->migration_blocker,
> > +                "vdpa %s vq %d group %"PRId64" is the same as cvq group "
> > +                "%"PRId64, nc->name, i, group, cvq_group);
> > +            goto out;
> >           }
> >       }
> >
> > @@ -468,8 +479,15 @@ static int vhost_vdpa_net_cvq_start(NetClientState *nc)
> >       s->vhost_vdpa.address_space_id = VHOST_VDPA_NET_CVQ_ASID;
> >
> >   out:
> > -    if (!s->vhost_vdpa.shadow_vqs_enabled) {
> > -        return 0;
> > +    if (s->migration_blocker) {
> > +        Error *errp = NULL;
> > +        r = migrate_add_blocker(s->migration_blocker, &errp);
> > +        if (unlikely(r != 0)) {
> > +            g_clear_pointer(&s->migration_blocker, error_free);
> > +            error_report_err(errp);
> > +        }
> > +
> > +        return r;
> >       }
> >
> >       s0 = vhost_vdpa_net_first_nc_vdpa(s);
> > @@ -513,6 +531,11 @@ static void vhost_vdpa_net_cvq_stop(NetClientState *nc)
> >           vhost_vdpa_cvq_unmap_buf(&s->vhost_vdpa, s->status);
> >       }
> >
> > +    if (s->migration_blocker) {
> > +        migrate_del_blocker(s->migration_blocker);
> > +        g_clear_pointer(&s->migration_blocker, error_free);
> > +    }
> > +
> >       vhost_vdpa_net_client_stop(nc);
> >   }
> >
>