Tested this patch with virtio-net regression tests, everything works fine. Tested-by: Lei Yang <[email protected]>
On Fri, Oct 31, 2025 at 2:06 PM Jason Wang <[email protected]> wrote: > > From: "Michael S. Tsirkin" <[email protected]> > > Changing alignment of header would mean it's no longer safe to cast a > 2 byte aligned pointer between formats. Use two 16 bit fields to make > it 2 byte aligned as previously. > > This fixes the performance regression since > commit ("virtio_net: enable gso over UDP tunnel support.") as it uses > virtio_net_hdr_v1_hash_tunnel which embeds > virtio_net_hdr_v1_hash. Pktgen in guest + XDP_DROP on TAP + vhost_net > shows the TX PPS is recovered from 2.4Mpps to 4.45Mpps. > > Fixes: 56a06bd40fab ("virtio_net: enable gso over UDP tunnel support.") > Cc: [email protected] > Signed-off-by: Michael S. Tsirkin <[email protected]> > Signed-off-by: Jason Wang <[email protected]> > --- > Changes since V1: > - Fix build issues of virtio_net_hdr_tnl_from_skb() > --- > drivers/net/virtio_net.c | 15 +++++++++++++-- > include/linux/virtio_net.h | 3 ++- > include/uapi/linux/virtio_net.h | 3 ++- > 3 files changed, 17 insertions(+), 4 deletions(-) > > diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c > index 8e8a179aaa49..e6e650bc3bc3 100644 > --- a/drivers/net/virtio_net.c > +++ b/drivers/net/virtio_net.c > @@ -2539,6 +2539,13 @@ static struct sk_buff *receive_mergeable(struct > net_device *dev, > return NULL; > } > > +static inline u32 > +virtio_net_hash_value(const struct virtio_net_hdr_v1_hash *hdr_hash) > +{ > + return __le16_to_cpu(hdr_hash->hash_value_lo) | > + (__le16_to_cpu(hdr_hash->hash_value_hi) << 16); > +} > + > static void virtio_skb_set_hash(const struct virtio_net_hdr_v1_hash > *hdr_hash, > struct sk_buff *skb) > { > @@ -2565,7 +2572,7 @@ static void virtio_skb_set_hash(const struct > virtio_net_hdr_v1_hash *hdr_hash, > default: > rss_hash_type = PKT_HASH_TYPE_NONE; > } > - skb_set_hash(skb, __le32_to_cpu(hdr_hash->hash_value), rss_hash_type); > + skb_set_hash(skb, virtio_net_hash_value(hdr_hash), rss_hash_type); > } > > static void virtnet_receive_done(struct virtnet_info *vi, struct > receive_queue *rq, > @@ -3311,6 +3318,10 @@ static int xmit_skb(struct send_queue *sq, struct > sk_buff *skb, bool orphan) > > pr_debug("%s: xmit %p %pM\n", vi->dev->name, skb, dest); > > + /* Make sure it's safe to cast between formats */ > + BUILD_BUG_ON(__alignof__(*hdr) != __alignof__(hdr->hash_hdr)); > + BUILD_BUG_ON(__alignof__(*hdr) != __alignof__(hdr->hash_hdr.hdr)); > + > can_push = vi->any_header_sg && > !((unsigned long)skb->data & (__alignof__(*hdr) - 1)) && > !skb_header_cloned(skb) && skb_headroom(skb) >= hdr_len; > @@ -6750,7 +6761,7 @@ static int virtnet_xdp_rx_hash(const struct xdp_md > *_ctx, u32 *hash, > hash_report = VIRTIO_NET_HASH_REPORT_NONE; > > *rss_type = virtnet_xdp_rss_type[hash_report]; > - *hash = __le32_to_cpu(hdr_hash->hash_value); > + *hash = virtio_net_hash_value(hdr_hash); > return 0; > } > > diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h > index 4d1780848d0e..b673c31569f3 100644 > --- a/include/linux/virtio_net.h > +++ b/include/linux/virtio_net.h > @@ -401,7 +401,8 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb, > if (!tnl_hdr_negotiated) > return -EINVAL; > > - vhdr->hash_hdr.hash_value = 0; > + vhdr->hash_hdr.hash_value_lo = 0; > + vhdr->hash_hdr.hash_value_hi = 0; > vhdr->hash_hdr.hash_report = 0; > vhdr->hash_hdr.padding = 0; > > diff --git a/include/uapi/linux/virtio_net.h b/include/uapi/linux/virtio_net.h > index 8bf27ab8bcb4..1db45b01532b 100644 > --- a/include/uapi/linux/virtio_net.h > +++ b/include/uapi/linux/virtio_net.h > @@ -193,7 +193,8 @@ struct virtio_net_hdr_v1 { > > struct virtio_net_hdr_v1_hash { > struct virtio_net_hdr_v1 hdr; > - __le32 hash_value; > + __le16 hash_value_lo; > + __le16 hash_value_hi; > #define VIRTIO_NET_HASH_REPORT_NONE 0 > #define VIRTIO_NET_HASH_REPORT_IPv4 1 > #define VIRTIO_NET_HASH_REPORT_TCPv4 2 > -- > 2.31.1 > >
