Re: [PATCH v2] net/virtio: deduce IP length for Virtio TSO checksum

[Maxime Coquelin <maxime.coquelin@redhat.com>]

On 3/3/23 12:19, Boleslav Stankevich wrote:
> The length of TSO payload could not fit into 16 bits provided by the
> IPv4 total length and IPv6 payload length fields. Thus, deduce it
> from the length of the packet.
> 
> Fixes: 696573046e9 ("net/virtio: support TSO")
> Cc: stable@dpdk.org
> 
> Signed-off-by: Boleslav Stankevich <boleslav.stankevich@oktetlabs.ru>
> Reviewed-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
> ---
>   drivers/net/virtio/virtio_rxtx.c | 25 ++++++++++++++++---------
>   1 file changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/virtio/virtio_rxtx.c b/drivers/net/virtio/virtio_rxtx.c
> index 2d0afd3302..e48ff3cca7 100644
> --- a/drivers/net/virtio/virtio_rxtx.c
> +++ b/drivers/net/virtio/virtio_rxtx.c
> @@ -404,29 +404,36 @@ virtio_tso_fix_cksum(struct rte_mbuf *m)
>   	if (likely(rte_pktmbuf_data_len(m) >= m->l2_len + m->l3_len +
>   			m->l4_len)) {
>   		struct rte_ipv4_hdr *iph;
> -		struct rte_ipv6_hdr *ip6h;
>   		struct rte_tcp_hdr *th;
> -		uint16_t prev_cksum, new_cksum, ip_len, ip_paylen;
> +		uint16_t prev_cksum, new_cksum;
> +		uint32_t ip_paylen;
>   		uint32_t tmp;
>   
>   		iph = rte_pktmbuf_mtod_offset(m,
>   					struct rte_ipv4_hdr *, m->l2_len);
>   		th = RTE_PTR_ADD(iph, m->l3_len);
> +
> +		/*
> +		 * Calculate IPv4 header checksum with current total length value
> +		 * (whatever it is) to have correct checksum after update on edits
> +		 * done by TSO.
> +		 */
>   		if ((iph->version_ihl >> 4) == 4) {
>   			iph->hdr_checksum = 0;
>   			iph->hdr_checksum = rte_ipv4_cksum(iph);
> -			ip_len = iph->total_length;
> -			ip_paylen = rte_cpu_to_be_16(rte_be_to_cpu_16(ip_len) -
> -				m->l3_len);
> -		} else {
> -			ip6h = (struct rte_ipv6_hdr *)iph;
> -			ip_paylen = ip6h->payload_len;
>   		}
>   
> +		/*
> +		 * Do not use IPv4 total length and IPv6 payload length fields to get
> +		 * TSO payload length since it could not fit into 16 bits.
> +		 */
> +		ip_paylen = rte_cpu_to_be_32(rte_pktmbuf_pkt_len(m) - m->l2_len -
> +					m->l3_len);
> +
>   		/* calculate the new phdr checksum not including ip_paylen */
>   		prev_cksum = th->cksum;
>   		tmp = prev_cksum;
> -		tmp += ip_paylen;
> +		tmp += (ip_paylen & 0xffff) + (ip_paylen >> 16);
>   		tmp = (tmp & 0xffff) + (tmp >> 16);
>   		new_cksum = tmp;
>   

Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>

Thanks,
Maxime