Subject: Re: [PATCH net-next v16 09/12] virtio_net: Implement IPv4 ethtool flow rules

From: "Michael S. Tsirkin" <[email-masked]>
Date: Thu, 22 Jan 2026 12:21:19 -0500

On Wed, Jan 21, 2026 at 04:06:49PM -0600, Daniel Jurgens wrote:
> Add support for IP_USER type rules from ethtool.
> 
> Example:
> $ ethtool -U ens9 flow-type ip4 src-ip 192.168.51.101 action -1
> Added rule with ID 1
> 
> The example rule will drop packets with the source IP specified.
> 
> Signed-off-by: Daniel Jurgens <[email-masked]>
> Reviewed-by: Parav Pandit <[email-masked]>
> Reviewed-by: Shahar Shitrit <[email-masked]>
> Reviewed-by: Xuan Zhuo <[email-masked]>
> ---
> v4:
>     - Fixed bug in protocol check of parse_ip4
>     - (u8 *) to (void *) casting.
>     - Alignment issues.
> 
> v12
>     - refactor calculate_flow_sizes to remove goto. MST
>     - refactor build_and_insert to remove goto validate. MST
>     - Move parse_ip4 l3_mask check to TCP/UDP patch. MST
>     - Check saddr/daddr mask before copying in parse_ip4. MST
>     - Remove tos check in setup_ip_key_mask.
>     - check l4_4_bytes mask is 0 in setup_ip_key_mask. MST
>     - changed return of setup_ip_key_mask to -EINVAL.
>     - BUG_ON if key overflows u8 size in calculate_flow_sizes. MST
> 
> v13:
>     - Set tos field if applicable in parse_ip4. MST
>     - Check tos in validate_ip4_mask. MST
>     - check l3_mask before setting addr and mask in parse_ip4. MST
>     - use has_ipv4 vs numhdrs for branching in build_and_insert. MST
> ---
> ---
>  drivers/net/virtio_net.c | 129 +++++++++++++++++++++++++++++++++++++--
>  1 file changed, 123 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index ba231f10b803..7ce120baeb41 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -5818,6 +5818,39 @@ static bool validate_eth_mask(const struct virtnet_ff *ff,
>  	return true;
>  }
>  
> +static bool validate_ip4_mask(const struct virtnet_ff *ff,
> +			      const struct virtio_net_ff_selector *sel,
> +			      const struct virtio_net_ff_selector *sel_cap)
> +{
> +	bool partial_mask = !!(sel_cap->flags & VIRTIO_NET_FF_MASK_F_PARTIAL_MASK);
> +	struct iphdr *cap, *mask;
> +
> +	cap = (struct iphdr *)&sel_cap->mask;
> +	mask = (struct iphdr *)&sel->mask;

this cast is only portable if sel and sel_cap are properly aligned.

Because if not then at least saddr/daddr accesses below are
not portable and need
Documentation/core-api/unaligned-memory-access.rst

> +
> +	if (mask->saddr &&
> +	    !check_mask_vs_cap(&mask->saddr, &cap->saddr,
> +			       sizeof(__be32), partial_mask))
> +		return false;
> +
> +	if (mask->daddr &&
> +	    !check_mask_vs_cap(&mask->daddr, &cap->daddr,
> +			       sizeof(__be32), partial_mask))
> +		return false;
> +
> +	if (mask->protocol &&
> +	    !check_mask_vs_cap(&mask->protocol, &cap->protocol,
> +			       sizeof(u8), partial_mask))
> +		return false;
> +
> +	if (mask->tos &&
> +	    !check_mask_vs_cap(&mask->tos, &cap->tos,
> +			       sizeof(u8), partial_mask))
> +		return false;
> +
> +	return true;
> +}
> +
>  static bool validate_mask(const struct virtnet_ff *ff,
>  			  const struct virtio_net_ff_selector *sel)
>  {
> @@ -5829,11 +5862,41 @@ static bool validate_mask(const struct virtnet_ff *ff,
>  	switch (sel->type) {
>  	case VIRTIO_NET_FF_MASK_TYPE_ETH:
>  		return validate_eth_mask(ff, sel, sel_cap);
> +
> +	case VIRTIO_NET_FF_MASK_TYPE_IPV4:
> +		return validate_ip4_mask(ff, sel, sel_cap);
>  	}
>  
>  	return false;
>  }
>  
> +static void parse_ip4(struct iphdr *mask, struct iphdr *key,
> +		      const struct ethtool_rx_flow_spec *fs)
> +{
> +	const struct ethtool_usrip4_spec *l3_mask = &fs->m_u.usr_ip4_spec;
> +	const struct ethtool_usrip4_spec *l3_val  = &fs->h_u.usr_ip4_spec;

this cast is only portable if sel and sel_cap are properly aligned.

Because if not then at least saddr/daddr accesses below are
not portable and need
Documentation/core-api/unaligned-memory-access.rst

> +
> +	if (l3_mask->ip4src) {
> +		mask->saddr = l3_mask->ip4src;
> +		key->saddr = l3_val->ip4src;
> +	}
> +
> +	if (l3_mask->ip4dst) {
> +		mask->daddr = l3_mask->ip4dst;
> +		key->daddr = l3_val->ip4dst;
> +	}
> +
> +	if (l3_mask->tos) {
> +		mask->tos = l3_mask->tos;
> +		key->tos = l3_val->tos;
> +	}
> +}
> +
> +static bool has_ipv4(u32 flow_type)
> +{
> +	return flow_type == IP_USER_FLOW;
> +}
> +
>  static int setup_classifier(struct virtnet_ff *ff,
>  			    struct virtnet_classifier **c)
>  {
> @@ -5969,6 +6032,7 @@ static bool supported_flow_type(const struct ethtool_rx_flow_spec *fs)
>  {
>  	switch (fs->flow_type) {
>  	case ETHER_FLOW:
> +	case IP_USER_FLOW:
>  		return true;
>  	}
>  
> @@ -6000,8 +6064,18 @@ static void calculate_flow_sizes(struct ethtool_rx_flow_spec *fs,
>  				 u8 *key_size, size_t *classifier_size,
>  				 int *num_hdrs)
>  {
> +	size_t size = sizeof(struct ethhdr);
> +
>  	*num_hdrs = 1;
> -	*key_size = sizeof(struct ethhdr);
> +
> +	if (fs->flow_type != ETHER_FLOW) {
> +		++(*num_hdrs);
> +		if (has_ipv4(fs->flow_type))
> +			size += sizeof(struct iphdr);
> +	}
> +
> +	BUG_ON(size > 0xff);
> +	*key_size = size;
>  	/*
>  	 * The classifier size is the size of the classifier header, a selector
>  	 * header for each type of header in the match criteria, and each header
> @@ -6013,8 +6087,9 @@ static void calculate_flow_sizes(struct ethtool_rx_flow_spec *fs,
>  }
>  
>  static void setup_eth_hdr_key_mask(struct virtio_net_ff_selector *selector,
> -				   u8 *key,
> -				   const struct ethtool_rx_flow_spec *fs)
> +				  u8 *key,
> +				  const struct ethtool_rx_flow_spec *fs,
> +				  int num_hdrs)
>  {
>  	struct ethhdr *eth_m = (struct ethhdr *)&selector->mask;
>  	struct ethhdr *eth_k = (struct ethhdr *)key;
> @@ -6022,8 +6097,35 @@ static void setup_eth_hdr_key_mask(struct virtio_net_ff_selector *selector,
>  	selector->type = VIRTIO_NET_FF_MASK_TYPE_ETH;
>  	selector->length = sizeof(struct ethhdr);
>  
> -	memcpy(eth_m, &fs->m_u.ether_spec, sizeof(*eth_m));
> -	memcpy(eth_k, &fs->h_u.ether_spec, sizeof(*eth_k));
> +	if (num_hdrs > 1) {
> +		eth_m->h_proto = cpu_to_be16(0xffff);
> +		eth_k->h_proto = cpu_to_be16(ETH_P_IP);
> +	} else {
> +		memcpy(eth_m, &fs->m_u.ether_spec, sizeof(*eth_m));
> +		memcpy(eth_k, &fs->h_u.ether_spec, sizeof(*eth_k));
> +	}
> +}
> +
> +static int setup_ip_key_mask(struct virtio_net_ff_selector *selector,
> +			     u8 *key,
> +			     const struct ethtool_rx_flow_spec *fs)
> +{
> +	struct iphdr *v4_m = (struct iphdr *)&selector->mask;
> +	struct iphdr *v4_k = (struct iphdr *)key;

Are mask and key guaranteed to be aligned here?

Because if not then at least saddr/daddr accesses in parse_ip4
call below are not portable and need
Documentation/core-api/unaligned-memory-access.rst

> +
> +	selector->type = VIRTIO_NET_FF_MASK_TYPE_IPV4;
> +	selector->length = sizeof(struct iphdr);
> +
> +	if (fs->h_u.usr_ip4_spec.l4_4_bytes ||
> +	    fs->h_u.usr_ip4_spec.ip_ver != ETH_RX_NFC_IP4 ||
> +	    fs->m_u.usr_ip4_spec.l4_4_bytes ||
> +	    fs->m_u.usr_ip4_spec.ip_ver ||
> +	    fs->m_u.usr_ip4_spec.proto)
> +		return -EINVAL;
> +
> +	parse_ip4(v4_m, v4_k, fs);
> +
> +	return 0;
>  }
>  
>  static int
> @@ -6045,6 +6147,13 @@ validate_classifier_selectors(struct virtnet_ff *ff,
>  	return 0;
>  }
>  
> +static
> +struct virtio_net_ff_selector *next_selector(struct virtio_net_ff_selector *sel)
> +{
> +	return (void *)sel + sizeof(struct virtio_net_ff_selector) +
> +		sel->length;
> +}
> +
>  static int build_and_insert(struct virtnet_ff *ff,
>  			    struct virtnet_ethtool_rule *eth_rule)
>  {
> @@ -6082,7 +6191,15 @@ static int build_and_insert(struct virtnet_ff *ff,
>  	classifier->count = num_hdrs;
>  	selector = (void *)&classifier->selectors[0];
>  
> -	setup_eth_hdr_key_mask(selector, key, fs);
> +	setup_eth_hdr_key_mask(selector, key, fs, num_hdrs);

So this will set sel->length to 14.

> +
> +	if (has_ipv4(fs->flow_type)) {
> +		selector = next_selector(selector);

And this will point next one at an offset 8 + 14 then?

> +
> +		err = setup_ip_key_mask(selector, key + sizeof(struct ethhdr), fs);

and this will pass unaligned mask and key?

> +		if (err)
> +			goto err_classifier;
> +	}
>  
>  	err = validate_classifier_selectors(ff, classifier, num_hdrs);
>  	if (err)
> -- 
> 2.50.1