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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jan 16, 2023 at 11:34:20AM +0800, Jason Wang wrote:
> 
> 在 2023/1/13 15:46, Eugenio Perez Martin 写道:
> > 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.
> 
> 
> This sounds a little bit tricky, more below:
> 
> 
> > 
> > For example, if the device does not support ASID it can be migrated as
> > long as _F_CVQ is not acked.
> 
> 
> The management may notice a non-consistent behavior in this case. I wonder
> if we can simply check the host features.
> 
> Thanks


Yes the issue is that ack can happen after migration started.
I don't think this kind of blocker appearing during migration
is currently expected/supported well. Is it?

> 
> > 
> > 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);
> > > >    }
> > > >