Re: [PATCH 12/12] vdpa: fix network breakage after cancelling migration

[Si-Wei Liu]

On 3/13/2024 11:12 AM, Michael Tokarev wrote:
> 14.02.2024 14:28, Si-Wei Liu wrote:
> > Fix an issue where cancellation of ongoing migration ends up
> > with no network connectivity.
> >
> > When canceling migration, SVQ will be switched back to the
> > passthrough mode, but the right call fd is not programed to
> > the device and the svq's own call fd is still used. At the
> > point of this transitioning period, the shadow_vqs_enabled
> > hadn't been set back to false yet, causing the installation
> > of call fd inadvertently bypassed.
> >
> > Fixes: a8ac88585da1 ("vhost: Add Shadow VirtQueue call forwarding 
> > capabilities")
> > Cc: Eugenio Pérez <eperezma@redhat.com>
> > Acked-by: Jason Wang <jasowang@redhat.com>
> > Signed-off-by: Si-Wei Liu <si-wei.liu@oracle.com>
> > ---
> >   hw/virtio/vhost-vdpa.c | 10 +++++++++-
> >   1 file changed, 9 insertions(+), 1 deletion(-)
>
> Is this a -stable material?
Probably yes, the pre-requisites of this patch are PATCH #10 and #11 
from this series (where SVQ_TSTATE_DISABLING gets defined and set).

> If yes, is it also applicable for stable-7.2 (mentioned commit is in 
> 7.2.0),
> which lacks v7.2.0-2327-gb276524386 "vdpa: Remember last call fd set",
> or should this one also be picked up?
Eugenio can judge, but seems to me the relevant code path cannot be 
effectively called as the dynamic SVQ feature (switching over to SVQ 
dynamically when migration is started) is not supported from 7.2. Maybe 
not worth it to cherry-pick this one to 7.2. Cherry-pick to stable-8.0 
and above should be applicable though (it needs some tweaks on patch #10 
to move svq_switching from @struct VhostVDPAShared to @struct vhost_vdpa).

Regards,
-Siwei

> Thanks,
>
> /mjt
>
> > diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > index 004110f..dfeca8b 100644
> > --- a/hw/virtio/vhost-vdpa.c
> > +++ b/hw/virtio/vhost-vdpa.c
> > @@ -1468,7 +1468,15 @@ static int vhost_vdpa_set_vring_call(struct 
> > vhost_dev *dev,
> >         /* Remember last call fd because we can switch to SVQ 
> > anytime. */
> >       vhost_svq_set_svq_call_fd(svq, file->fd);
> > -    if (v->shadow_vqs_enabled) {
> > +    /*
> > +     * When SVQ is transitioning to off, shadow_vqs_enabled has
> > +     * not been set back to false yet, but the underlying call fd
> > +     * will have to switch back to the guest notifier to signal the
> > +     * passthrough virtqueues. In other situations, SVQ's own call
> > +     * fd shall be used to signal the device model.
> > +     */
> > +    if (v->shadow_vqs_enabled &&
> > +        v->shared->svq_switching != SVQ_TSTATE_DISABLING) {
> >           return 0;
> >       }