Re: [RFC 2/2] virtio-net: use post load hook

[Mikhail Sennikovsky]

Hi Michael,

Unfortunately your approach will not work, because the
VirtIONet::curr_guest_offloads would still be reset in
virtio_net_set_features:
--
if (n->has_vnet_hdr) {
    n->curr_guest_offloads =
        virtio_net_guest_offloads_by_features(features);
--
( https://github.com/qemu/qemu/blob/master/hw/net/virtio-net.c#L774 )

I.e. although virtio_net_apply_guest_offloads would now be called
after the virtio_net_set_features, by the time it is called the
VirtIONet::curr_guest_offloads would be reset to a full list of
features.

Regards,
Mikhail

Am Do., 10. Okt. 2019 um 20:04 Uhr schrieb Michael S. Tsirkin <address@hidden>:
>
> Currently offloads disabled by guest via the 
> VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET
> command are not preserved on VM migration.
> Instead all offloads reported by guest features (via 
> VIRTIO_PCI_GUEST_FEATURES)
> get enabled.
> What happens is: first the VirtIONet::curr_guest_offloads gets restored
> and offloads are getting set correctly:
>
>  #0  qemu_set_offload (nc=0x555556a11400, csum=1, tso4=0, tso6=0, ecn=0, 
> ufo=0) at net/net.c:474
>  #1  virtio_net_apply_guest_offloads (n=0x555557701ca0) at 
> hw/net/virtio-net.c:720
>  #2  virtio_net_post_load_device (opaque=0x555557701ca0, version_id=11) at 
> hw/net/virtio-net.c:2334
>  #3  vmstate_load_state (f=0x5555569dc010, vmsd=0x555556577c80 
> <vmstate_virtio_net_device>, opaque=0x555557701ca0, version_id=11)
>      at migration/vmstate.c:168
>  #4  virtio_load (vdev=0x555557701ca0, f=0x5555569dc010, version_id=11) at 
> hw/virtio/virtio.c:2197
>  #5  virtio_device_get (f=0x5555569dc010, opaque=0x555557701ca0, size=0, 
> field=0x55555668cd00 <__compound_literal.5>) at hw/virtio/virtio.c:2036
>  #6  vmstate_load_state (f=0x5555569dc010, vmsd=0x555556577ce0 
> <vmstate_virtio_net>, opaque=0x555557701ca0, version_id=11) at 
> migration/vmstate.c:143
>  #7  vmstate_load (f=0x5555569dc010, se=0x5555578189e0) at 
> migration/savevm.c:829
>  #8  qemu_loadvm_section_start_full (f=0x5555569dc010, mis=0x5555569eee20) at 
> migration/savevm.c:2211
>  #9  qemu_loadvm_state_main (f=0x5555569dc010, mis=0x5555569eee20) at 
> migration/savevm.c:2395
>  #10 qemu_loadvm_state (f=0x5555569dc010) at migration/savevm.c:2467
>  #11 process_incoming_migration_co (opaque=0x0) at migration/migration.c:449
>
> However later on the features are getting restored, and offloads get reset to
> everything supported by features:
>
>  #0  qemu_set_offload (nc=0x555556a11400, csum=1, tso4=1, tso6=1, ecn=0, 
> ufo=0) at net/net.c:474
>  #1  virtio_net_apply_guest_offloads (n=0x555557701ca0) at 
> hw/net/virtio-net.c:720
>  #2  virtio_net_set_features (vdev=0x555557701ca0, features=5104441767) at 
> hw/net/virtio-net.c:773
>  #3  virtio_set_features_nocheck (vdev=0x555557701ca0, val=5104441767) at 
> hw/virtio/virtio.c:2052
>  #4  virtio_load (vdev=0x555557701ca0, f=0x5555569dc010, version_id=11) at 
> hw/virtio/virtio.c:2220
>  #5  virtio_device_get (f=0x5555569dc010, opaque=0x555557701ca0, size=0, 
> field=0x55555668cd00 <__compound_literal.5>) at hw/virtio/virtio.c:2036
>  #6  vmstate_load_state (f=0x5555569dc010, vmsd=0x555556577ce0 
> <vmstate_virtio_net>, opaque=0x555557701ca0, version_id=11) at 
> migration/vmstate.c:143
>  #7  vmstate_load (f=0x5555569dc010, se=0x5555578189e0) at 
> migration/savevm.c:829
>  #8  qemu_loadvm_section_start_full (f=0x5555569dc010, mis=0x5555569eee20) at 
> migration/savevm.c:2211
>  #9  qemu_loadvm_state_main (f=0x5555569dc010, mis=0x5555569eee20) at 
> migration/savevm.c:2395
>  #10 qemu_loadvm_state (f=0x5555569dc010) at migration/savevm.c:2467
>  #11 process_incoming_migration_co (opaque=0x0) at migration/migration.c:449
>
> Fix this by pushing out offload initialization to the new post load hook.
>
> Reported-by: Mikhail Sennikovsky <address@hidden>
> Signed-off-by: Michael S. Tsirkin <address@hidden>
> ---
>  hw/net/virtio-net.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index 9f11422337..62fb858e2d 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -2333,10 +2333,6 @@ static int virtio_net_post_load_device(void *opaque, 
> int version_id)
>          n->curr_guest_offloads = virtio_net_supported_guest_offloads(n);
>      }
>
> -    if (peer_has_vnet_hdr(n)) {
> -        virtio_net_apply_guest_offloads(n);
> -    }
> -
>      virtio_net_set_queues(n);
>
>      /* Find the first multicast entry in the saved MAC filter */
> @@ -2370,6 +2366,15 @@ static int virtio_net_post_load_device(void *opaque, 
> int version_id)
>      return 0;
>  }
>
> +static int virtio_net_post_load_virtio(VirtIODevice *vdev)
> +{
> +    if (peer_has_vnet_hdr(n)) {
> +        virtio_net_apply_guest_offloads(n);
> +    }
> +
> +    return 0;
> +}
> +
>  /* tx_waiting field of a VirtIONetQueue */
>  static const VMStateDescription vmstate_virtio_net_queue_tx_waiting = {
>      .name = "virtio-net-queue-tx_waiting",
> @@ -2912,6 +2917,7 @@ static void virtio_net_class_init(ObjectClass *klass, 
> void *data)
>      vdc->guest_notifier_mask = virtio_net_guest_notifier_mask;
>      vdc->guest_notifier_pending = virtio_net_guest_notifier_pending;
>      vdc->legacy_features |= (0x1 << VIRTIO_NET_F_GSO);
> +    vdc->post_load = virtio_net_post_load_virtio;
>      vdc->vmsd = &vmstate_virtio_net_device;
>  }
>
> --
> MST
>