It is incorrect to have the VIRTIO_NET_HDR_F_NEEDS_CSUM set when
checksum offloading is disabled so clear the bit.

TCP/UDP checksum is usually offloaded when the peer requires virtio
headers because they can instruct the peer to compute checksum. However,
igb disables TX checksum offloading when a VF is enabled whether the
peer requires virtio headers because a transmitted packet can be routed
to it and it expects the packet has a proper checksum. Therefore, it
is necessary to have a correct virtio header even when checksum
offloading is disabled.

A real TCP/UDP checksum will be computed and saved in the buffer when
checksum offloading is disabled. The virtio specification requires to
set the packet checksum stored in the buffer to the TCP/UDP pseudo
header when the VIRTIO_NET_HDR_F_NEEDS_CSUM bit is set so the bit must
be cleared in that case.

Fixes: ffbd2dbd8e64 ("e1000e: Perform software segmentation for loopback")
Buglink: https://issues.redhat.com/browse/RHEL-23067
Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
---
Changes in v2:
- Dropped VIRTIO_NET_HDR_F_DATA_VALID. (Jason Wang)
- Link to v1: https://lore.kernel.org/r/20240324-tx-v1-1-a3b4135749ec@daynix.com
---
 hw/net/net_tx_pkt.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/hw/net/net_tx_pkt.c b/hw/net/net_tx_pkt.c
index 2e5f58b3c9cc..2134a18c4c90 100644
--- a/hw/net/net_tx_pkt.c
+++ b/hw/net/net_tx_pkt.c
@@ -833,6 +833,7 @@ bool net_tx_pkt_send_custom(struct NetTxPkt *pkt, bool offload,
 
     if (offload || gso_type == VIRTIO_NET_HDR_GSO_NONE) {
         if (!offload && pkt->virt_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
+            pkt->virt_hdr.flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;
             net_tx_pkt_do_sw_csum(pkt, &pkt->vec[NET_TX_PKT_L2HDR_FRAG],
                                   pkt->payload_frags + NET_TX_PKT_PL_START_FRAG - 1,
                                   pkt->payload_len);

---
base-commit: ba49d760eb04630e7b15f423ebecf6c871b8f77b
change-id: 20240324-tx-c57d3c22ad73

Best regards,
-- 
Akihiko Odaki <akihiko.odaki@daynix.com>

On Wed, Mar 27, 2024 at 4:43 PM Akihiko Odaki <akihiko.odaki@daynix.com> wrote:
>
> It is incorrect to have the VIRTIO_NET_HDR_F_NEEDS_CSUM set when
> checksum offloading is disabled so clear the bit.
>
> TCP/UDP checksum is usually offloaded when the peer requires virtio
> headers because they can instruct the peer to compute checksum. However,
> igb disables TX checksum offloading when a VF is enabled whether the
> peer requires virtio headers because a transmitted packet can be routed
> to it and it expects the packet has a proper checksum. Therefore, it
> is necessary to have a correct virtio header even when checksum
> offloading is disabled.
>
> A real TCP/UDP checksum will be computed and saved in the buffer when
> checksum offloading is disabled. The virtio specification requires to
> set the packet checksum stored in the buffer to the TCP/UDP pseudo
> header when the VIRTIO_NET_HDR_F_NEEDS_CSUM bit is set so the bit must
> be cleared in that case.
>
> Fixes: ffbd2dbd8e64 ("e1000e: Perform software segmentation for loopback")
> Buglink: https://issues.redhat.com/browse/RHEL-23067
> Signed-off-by: Akihiko Odaki <akihiko.odaki@daynix.com>
> ---
> Changes in v2:
> - Dropped VIRTIO_NET_HDR_F_DATA_VALID. (Jason Wang)
> - Link to v1: https://lore.kernel.org/r/20240324-tx-v1-1-a3b4135749ec@daynix.com

Queued.

Thanks

> ---
>  hw/net/net_tx_pkt.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/hw/net/net_tx_pkt.c b/hw/net/net_tx_pkt.c
> index 2e5f58b3c9cc..2134a18c4c90 100644
> --- a/hw/net/net_tx_pkt.c
> +++ b/hw/net/net_tx_pkt.c
> @@ -833,6 +833,7 @@ bool net_tx_pkt_send_custom(struct NetTxPkt *pkt, bool offload,
>
>      if (offload || gso_type == VIRTIO_NET_HDR_GSO_NONE) {
>          if (!offload && pkt->virt_hdr.flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
> +            pkt->virt_hdr.flags &= ~VIRTIO_NET_HDR_F_NEEDS_CSUM;
>              net_tx_pkt_do_sw_csum(pkt, &pkt->vec[NET_TX_PKT_L2HDR_FRAG],
>                                    pkt->payload_frags + NET_TX_PKT_PL_START_FRAG - 1,
>                                    pkt->payload_len);
>
> ---
> base-commit: ba49d760eb04630e7b15f423ebecf6c871b8f77b
> change-id: 20240324-tx-c57d3c22ad73
>
> Best regards,
> --
> Akihiko Odaki <akihiko.odaki@daynix.com>
>