Re: [PATCH net-next V2 5/5] virtio-net: switch off offloads on demand if possible on XDP set

[Jason Wang]

On 2017年07月25日 05:29, Michael S. Tsirkin wrote:
On Wed, Jul 19, 2017 at 04:54:49PM +0800, Jason Wang wrote:
Current XDP implementation wants guest offloads feature to be disabled
on device. This is inconvenient and means guest can't benefit from
offloads if XDP is not used. This patch tries to address this
limitation by disabling the offloads on demand through control guest
offloads. Guest offloads will be disabled and enabled on demand on XDP
set.

Signed-off-by: Jason Wang <jasow...@redhat.com>
Doesn't look like my comments on v1 were addressed.
Copying here:

In fact, since we no longer reset when XDP is set,
here device might have offloads enabled, buffers are
used but not consumed, then XDP is set.

This can result in
- packet scattered across multiple buffers
   (handled correctly but need to update the comment)

We drop all gso packet now, so this won't happen.

- packet may have VIRTIO_NET_HDR_F_NEEDS_CSUM, in that case
   the spec says "The checksum on the packet is incomplete".
   (probably needs to be handled by calculating the checksum).

This needs to be fixed, but it was not introduced by this commit but:

b00f70b0dacb virtio-net: unbreak csumed packets for XDP_PASS which 
allows NEEDS_CSUM for mergeable buffer
bb91accf2733 virtio-net: XDP support for small buffers which forbid 
checksumed packet for small buffer

Will post a patch to checksum the packet.

Thanks


Jason, as David applied this patch already, can you comment
on the issues please?

---
  drivers/net/virtio_net.c | 70 ++++++++++++++++++++++++++++++++++++++++++++----
  1 file changed, 65 insertions(+), 5 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index b3fc01d..5fbd15e 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -57,6 +57,11 @@ DECLARE_EWMA(pkt_len, 0, 64)
  
  #define VIRTNET_DRIVER_VERSION "1.0.0"
  
+const unsigned long guest_offloads[] = { VIRTIO_NET_F_GUEST_TSO4,
+                                        VIRTIO_NET_F_GUEST_TSO6,
+                                        VIRTIO_NET_F_GUEST_ECN,
+                                        VIRTIO_NET_F_GUEST_UFO };
+
  struct virtnet_stats {
        struct u64_stats_sync tx_syncp;
        struct u64_stats_sync rx_syncp;
@@ -164,10 +169,13 @@ struct virtnet_info {
        u8 ctrl_promisc;
        u8 ctrl_allmulti;
        u16 ctrl_vid;
+       u64 ctrl_offloads;
  
  	/* Ethtool settings */
        u8 duplex;
        u32 speed;
+
+       unsigned long guest_offloads;
  };
  
  struct padded_vnet_hdr {
@@ -1896,6 +1904,47 @@ static int virtnet_restore_up(struct virtio_device *vdev)
        return err;
  }
  
+static int virtnet_set_guest_offloads(struct virtnet_info *vi, u64 offloads)
+{
+       struct scatterlist sg;
+       vi->ctrl_offloads = cpu_to_virtio64(vi->vdev, offloads);
+
+       sg_init_one(&sg, &vi->ctrl_offloads, sizeof(vi->ctrl_offloads));
+
+       if (!virtnet_send_command(vi, VIRTIO_NET_CTRL_GUEST_OFFLOADS,
+                                 VIRTIO_NET_CTRL_GUEST_OFFLOADS_SET, &sg)) {
+               dev_warn(&vi->dev->dev, "Fail to set guest offload. \n");
+               return -EINVAL;
+       }
+
+       return 0;
+}
+
+static int virtnet_clear_guest_offloads(struct virtnet_info *vi)
+{
+       u64 offloads = 0;
+
+       if (!vi->guest_offloads)
+               return 0;
+
+       if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))
+               offloads = 1ULL << VIRTIO_NET_F_GUEST_CSUM;
+
+       return virtnet_set_guest_offloads(vi, offloads);
+}
+
+static int virtnet_restore_guest_offloads(struct virtnet_info *vi)
+{
+       u64 offloads = vi->guest_offloads;
+
+       if (!vi->guest_offloads)
+               return 0;
+       if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_CSUM))
+               offloads |= 1ULL << VIRTIO_NET_F_GUEST_CSUM;
+
+       return virtnet_set_guest_offloads(vi, offloads);
+}
+
  static int virtnet_xdp_set(struct net_device *dev, struct bpf_prog *prog,
                           struct netlink_ext_ack *extack)
  {
@@ -1905,10 +1954,11 @@ static int virtnet_xdp_set(struct net_device *dev, 
struct bpf_prog *prog,
        u16 xdp_qp = 0, curr_qp;
        int i, err;
  
-	if (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
-           virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
-           virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
-           virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO)) {
+       if (!virtio_has_feature(vi->vdev, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS)
+           && (virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO4) ||
+               virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_TSO6) ||
+               virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_ECN) ||
+               virtio_has_feature(vi->vdev, VIRTIO_NET_F_GUEST_UFO))) {
                NL_SET_ERR_MSG_MOD(extack, "Can't set XDP while host is implementing 
LRO, disable LRO first");
                return -EOPNOTSUPP;
        }
@@ -1955,6 +2005,12 @@ static int virtnet_xdp_set(struct net_device *dev, 
struct bpf_prog *prog,
        for (i = 0; i < vi->max_queue_pairs; i++) {
                old_prog = rtnl_dereference(vi->rq[i].xdp_prog);
                rcu_assign_pointer(vi->rq[i].xdp_prog, prog);
+               if (i == 0) {
+                       if (!old_prog)
+                               virtnet_clear_guest_offloads(vi);
+                       if (!prog)
+                               virtnet_restore_guest_offloads(vi);
+               }
                if (old_prog)
                        bpf_prog_put(old_prog);
                virtnet_napi_enable(vi->rq[i].vq, &vi->rq[i].napi);
@@ -2588,6 +2644,10 @@ static int virtnet_probe(struct virtio_device *vdev)
                netif_carrier_on(dev);
        }
  
+	for (i = 0; i < ARRAY_SIZE(guest_offloads); i++)
+               if (virtio_has_feature(vi->vdev, guest_offloads[i]))
+                       set_bit(guest_offloads[i], &vi->guest_offloads);
+
        pr_debug("virtnet: registered device %s with %d RX and TX vq's\n",
                 dev->name, max_queue_pairs);
  
@@ -2684,7 +2744,7 @@ static struct virtio_device_id id_table[] = {
        VIRTIO_NET_F_CTRL_RX, VIRTIO_NET_F_CTRL_VLAN, \
        VIRTIO_NET_F_GUEST_ANNOUNCE, VIRTIO_NET_F_MQ, \
        VIRTIO_NET_F_CTRL_MAC_ADDR, \
-       VIRTIO_NET_F_MTU
+       VIRTIO_NET_F_MTU, VIRTIO_NET_F_CTRL_GUEST_OFFLOADS
  
  static unsigned int features[] = {
        VIRTNET_FEATURES,
--
2.7.4