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virtio_net: fix alignment for virtio_net_hdr_v1_hash

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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: 56a06bd40f ("virtio_net: enable gso over UDP tunnel support.")
Cc: stable@vger.kernel.org
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Link: https://patch.msgid.link/20251031060551.126-1-jasowang@redhat.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Michael S. Tsirkin
2025-10-31 14:05:51 +08:00
committed by Jakub Kicinski
parent e120f46768
commit c3838262b8
3 changed files with 17 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

15
drivers/net/virtio_net.c
View File

@@ -2539,6 +2539,13 @@ err_buf:
return NULL; 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, static void virtio_skb_set_hash(const struct virtio_net_hdr_v1_hash *hdr_hash,
struct sk_buff *skb) struct sk_buff *skb)
{ {
@@ -2565,7 +2572,7 @@ static void virtio_skb_set_hash(const struct virtio_net_hdr_v1_hash *hdr_hash,
default: default:
rss_hash_type = PKT_HASH_TYPE_NONE; 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, 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); 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 && can_push = vi->any_header_sg &&
!((unsigned long)skb->data & (__alignof__(*hdr) - 1)) && !((unsigned long)skb->data & (__alignof__(*hdr) - 1)) &&
!skb_header_cloned(skb) && skb_headroom(skb) >= hdr_len; !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; hash_report = VIRTIO_NET_HASH_REPORT_NONE;
*rss_type = virtnet_xdp_rss_type[hash_report]; *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; return 0;
} }

3
include/linux/virtio_net.h
View File

@@ -401,7 +401,8 @@ virtio_net_hdr_tnl_from_skb(const struct sk_buff *skb,
if (!tnl_hdr_negotiated) if (!tnl_hdr_negotiated)
return -EINVAL; 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.hash_report = 0;
vhdr->hash_hdr.padding = 0; vhdr->hash_hdr.padding = 0;

3
include/uapi/linux/virtio_net.h
View File

@@ -193,7 +193,8 @@ struct virtio_net_hdr_v1 {
struct virtio_net_hdr_v1_hash { struct virtio_net_hdr_v1_hash {
struct virtio_net_hdr_v1 hdr; 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_NONE 0
#define VIRTIO_NET_HASH_REPORT_IPv4 1 #define VIRTIO_NET_HASH_REPORT_IPv4 1
#define VIRTIO_NET_HASH_REPORT_TCPv4 2 #define VIRTIO_NET_HASH_REPORT_TCPv4 2