Re: [PATCH 2/3] vdpa: load vlan configuration at NIC startup

[Eugenio Perez Martin]

On Wed, Sep 14, 2022 at 1:33 PM Si-Wei Liu <si-wei.liu@oracle.com> wrote:
>
>
>
> On 9/14/2022 3:20 AM, Jason Wang wrote:
> > On Fri, Sep 9, 2022 at 4:02 PM Eugenio Perez Martin <eperezma@redhat.com> 
> > wrote:
> >> On Fri, Sep 9, 2022 at 8:40 AM Jason Wang <jasowang@redhat.com> wrote:
> >>> On Fri, Sep 9, 2022 at 2:38 PM Jason Wang <jasowang@redhat.com> wrote:
> >>>> On Wed, Sep 7, 2022 at 12:36 AM Eugenio Pérez <eperezma@redhat.com> 
> >>>> wrote:
> >>>>> To have enabled vlans at device startup may happen in the destination of
> >>>>> a live migration, so this configuration must be restored.
> >>>>>
> >>>>> At this moment the code is not accessible, since SVQ refuses to start if
> >>>>> vlan feature is exposed by the device.
> >>>>>
> >>>>> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> >>>>> ---
> >>>>>   net/vhost-vdpa.c | 46 ++++++++++++++++++++++++++++++++++++++++++++--
> >>>>>   1 file changed, 44 insertions(+), 2 deletions(-)
> >>>>>
> >>>>> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> >>>>> index 4bc3fd01a8..ecbfd08eb9 100644
> >>>>> --- a/net/vhost-vdpa.c
> >>>>> +++ b/net/vhost-vdpa.c
> >>>>> @@ -100,6 +100,8 @@ static const uint64_t vdpa_svq_device_features =
> >>>>>       BIT_ULL(VIRTIO_NET_F_RSC_EXT) |
> >>>>>       BIT_ULL(VIRTIO_NET_F_STANDBY);
> >>>>>
> >>>>> +#define MAX_VLAN    (1 << 12)   /* Per 802.1Q definition */
> >>>>> +
> >>>>>   VHostNetState *vhost_vdpa_get_vhost_net(NetClientState *nc)
> >>>>>   {
> >>>>>       VhostVDPAState *s = DO_UPCAST(VhostVDPAState, nc, nc);
> >>>>> @@ -423,6 +425,47 @@ static int vhost_vdpa_net_load_mq(VhostVDPAState 
> >>>>> *s,
> >>>>>       return *s->status != VIRTIO_NET_OK;
> >>>>>   }
> >>>>>
> >>>>> +static int vhost_vdpa_net_load_single_vlan(VhostVDPAState *s,
> >>>>> +                                           const VirtIONet *n,
> >>>>> +                                           uint16_t vid)
> >>>>> +{
> >>>>> +    ssize_t dev_written = vhost_vdpa_net_load_cmd(s, 
> >>>>> VIRTIO_NET_CTRL_VLAN,
> >>>>> +                                                  
> >>>>> VIRTIO_NET_CTRL_VLAN_ADD,
> >>>>> +                                                  &vid, sizeof(vid));
> >>>>> +    if (unlikely(dev_written < 0)) {
> >>>>> +        return dev_written;
> >>>>> +    }
> >>>>> +
> >>>>> +    if (unlikely(*s->status != VIRTIO_NET_OK)) {
> >>>>> +        return -EINVAL;
> >>>>> +    }
> >>>>> +
> >>>>> +    return 0;
> >>>>> +}
> >>>>> +
> >>>>> +static int vhost_vdpa_net_load_vlan(VhostVDPAState *s,
> >>>>> +                                    const VirtIONet *n)
> >>>>> +{
> >>>>> +    uint64_t features = n->parent_obj.guest_features;
> >>>>> +
> >>>>> +    if (!(features & BIT_ULL(VIRTIO_NET_F_CTRL_VLAN))) {
> >>>>> +        return 0;
> >>>>> +    }
> >>>>> +
> >>>>> +    for (int i = 0; i < MAX_VLAN >> 5; i++) {
> >>>>> +        for (int j = 0; n->vlans[i] && j <= 0x1f; j++) {
> >>>>> +            if (n->vlans[i] & (1U << j)) {
> >>>>> +                int r = vhost_vdpa_net_load_single_vlan(s, n, (i << 5) 
> >>>>> + j);
> >>>> This seems to cause a lot of latency if the driver has a lot of vlans.
> >>>>
> >>>> I wonder if it's simply to let all vlan traffic go by disabling
> >>>> CTRL_VLAN feature at vDPA layer.
> >> The guest will not be able to recover that vlan configuration.
> > Spec said it's best effort and we actually don't do this for
> > vhost-net/user for years and manage to survive.
> I thought there's a border line between best effort and do nothing. ;-)
>

I also think it is worth at least trying to migrate it for sure. For
MAC there may be too many entries, but VLAN should be totally
manageable (and the information is already there, the bitmap is
actually being migrated).

> I think that the reason this could survive is really software
> implementation specific - say if the backend doesn't start with VLAN
> filtering disabled (meaning allow all VLAN traffic to pass) then it
> would become a problem. This won't be a problem for almost PF NICs but
> may be problematic for vDPA e.g. VF backed VDPAs.

I'd say the driver would expect all vlan filters to be cleared after a
reset, isn't it? The spec doesn't explicitly say anything about that
as far as I see.

> >
> >>> Another idea is to extend the spec to allow us to accept a bitmap of
> >>> the vlan ids via a single command, then we will be fine.
> >>>
> >> I'm not sure if adding more ways to configure something is the answer,
> >> but I'd be ok to implement it.
> >>
> >> Another idea is to allow the sending of many CVQ commands in parallel.
> >> It shouldn't be very hard to achieve using exposed buffers as ring
> >> buffers, and it will short down the start of the devices with many
> >> features.
> > In the extreme case, what if guests decide to filter all of the vlans?
> > It means we need MAX_VLAN commands which may exceeds the size of the
> > control virtqueue.
> Indeed, that's a case where a single flat device state blob would be
> more efficient for hardware drivers to apply than individual control
> command messages do.
>

If we're going that route, being able to set a bitmap for vlan
filtering (Jason's proposal) seems to solve more issues in the same
shot, doesn't it?

Thanks!