Subject: Re: [xdp-hints] [RFC bpf-next 03/23] ice: make RX checksum checking code more reusable

From: Larysa Zaremba <[email-masked]>
Date: Mon, 4 Sep 2023 20:01:06 +0200

On Mon, Sep 04, 2023 at 05:02:40PM +0200, Maciej Fijalkowski wrote:
> On Thu, Aug 24, 2023 at 09:26:42PM +0200, Larysa Zaremba wrote:
> > Previously, we only needed RX checksum flags in skb path,
> > hence all related code was written with skb in mind.
> > But with the addition of XDP hints via kfuncs to the ice driver,
> > the same logic will be needed in .xmo_() callbacks.
> > 
> > Put generic process of determining checksum status into
> > a separate function.
> > 
> > Now we cannot operate directly on skb, when deducing
> > checksum status, therefore introduce an intermediate enum for checksum
> > status. Fortunately, in ice, we have only 4 possibilities: checksum
> > validated at level 0, validated at level 1, no checksum, checksum error.
> > Use 3 bits for more convenient conversion.
> > 
> > Signed-off-by: Larysa Zaremba <[email-masked]>
> > ---
> >  drivers/net/ethernet/intel/ice/ice_txrx_lib.c | 105 ++++++++++++------
> >  1 file changed, 69 insertions(+), 36 deletions(-)
> > 
> > diff --git a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > index b2f241b73934..8b155a502b3b 100644
> > --- a/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > +++ b/drivers/net/ethernet/intel/ice/ice_txrx_lib.c
> > @@ -102,18 +102,41 @@ ice_rx_hash_to_skb(const struct ice_rx_ring *rx_ring,
> >  		skb_set_hash(skb, hash, ice_ptype_to_htype(rx_ptype));
> >  }
> >  
> > +enum ice_rx_csum_status {
> > +	ICE_RX_CSUM_LVL_0	= 0,
> > +	ICE_RX_CSUM_LVL_1	= BIT(0),
> > +	ICE_RX_CSUM_NONE	= BIT(1),
> > +	ICE_RX_CSUM_ERROR	= BIT(2),
> > +	ICE_RX_CSUM_FAIL	= ICE_RX_CSUM_NONE | ICE_RX_CSUM_ERROR,
> > +};
> > +
> >  /**
> > - * ice_rx_csum - Indicate in skb if checksum is good
> > - * @ring: the ring we care about
> > - * @skb: skb currently being received and modified
> > + * ice_rx_csum_lvl - Get checksum level from status
> > + * @status: driver-specific checksum status
> > + */
> > +static u8 ice_rx_csum_lvl(enum ice_rx_csum_status status)
> > +{
> > +	return status & ICE_RX_CSUM_LVL_1;
> > +}
> > +
> > +/**
> > + * ice_rx_csum_ip_summed - Checksum status from driver-specific to generic
> > + * @status: driver-specific checksum status
> > + */
> > +static u8 ice_rx_csum_ip_summed(enum ice_rx_csum_status status)
> > +{
> > +	return status & ICE_RX_CSUM_NONE ? CHECKSUM_NONE : CHECKSUM_UNNECESSARY;
> 
> 	return !(status & ICE_RX_CSUM_NONE);
> 
> ?

status & ICE_RX_CSUM_NONE ? CHECKSUM_NONE : CHECKSUM_UNNECESSARY;

is immediately understandable and results in 3 asm operations (I have checked):

result = status >> 1;
result ^= 1;
result &= 1;

I do not think "!(status & ICE_RX_CSUM_NONE);" could produce less.

> 
> > +}
> > +
> > +/**
> > + * ice_get_rx_csum_status - Deduce checksum status from descriptor
> >   * @rx_desc: the receive descriptor
> >   * @ptype: the packet type decoded by hardware
> >   *
> > - * skb->protocol must be set before this function is called
> > + * Returns driver-specific checksum status
> >   */
> > -static void
> > -ice_rx_csum(struct ice_rx_ring *ring, struct sk_buff *skb,
> > -	    union ice_32b_rx_flex_desc *rx_desc, u16 ptype)
> > +static enum ice_rx_csum_status
> > +ice_get_rx_csum_status(const union ice_32b_rx_flex_desc *rx_desc, u16 ptype)
> >  {
> >  	struct ice_rx_ptype_decoded decoded;
> >  	u16 rx_status0, rx_status1;
> > @@ -124,20 +147,12 @@ ice_rx_csum(struct ice_rx_ring *ring, struct sk_buff *skb,
> >  
> >  	decoded = ice_decode_rx_desc_ptype(ptype);
> >  
> > -	/* Start with CHECKSUM_NONE and by default csum_level = 0 */
> > -	skb->ip_summed = CHECKSUM_NONE;
> > -	skb_checksum_none_assert(skb);
> > -
> > -	/* check if Rx checksum is enabled */
> > -	if (!(ring->netdev->features & NETIF_F_RXCSUM))
> > -		return;
> > -
> >  	/* check if HW has decoded the packet and checksum */
> >  	if (!(rx_status0 & BIT(ICE_RX_FLEX_DESC_STATUS0_L3L4P_S)))
> > -		return;
> > +		return ICE_RX_CSUM_NONE;
> >  
> >  	if (!(decoded.known && decoded.outer_ip))
> > -		return;
> > +		return ICE_RX_CSUM_NONE;
> >  
> >  	ipv4 = (decoded.outer_ip == ICE_RX_PTYPE_OUTER_IP) &&
> >  	       (decoded.outer_ip_ver == ICE_RX_PTYPE_OUTER_IPV4);
> > @@ -146,43 +161,61 @@ ice_rx_csum(struct ice_rx_ring *ring, struct sk_buff *skb,
> >  
> >  	if (ipv4 && (rx_status0 & (BIT(ICE_RX_FLEX_DESC_STATUS0_XSUM_IPE_S) |
> >  				   BIT(ICE_RX_FLEX_DESC_STATUS0_XSUM_EIPE_S))))
> > -		goto checksum_fail;
> > +		return ICE_RX_CSUM_FAIL;
> >  
> >  	if (ipv6 && (rx_status0 & (BIT(ICE_RX_FLEX_DESC_STATUS0_IPV6EXADD_S))))
> > -		goto checksum_fail;
> > +		return ICE_RX_CSUM_FAIL;
> >  
> >  	/* check for L4 errors and handle packets that were not able to be
> >  	 * checksummed due to arrival speed
> >  	 */
> >  	if (rx_status0 & BIT(ICE_RX_FLEX_DESC_STATUS0_XSUM_L4E_S))
> > -		goto checksum_fail;
> > +		return ICE_RX_CSUM_FAIL;
> >  
> >  	/* check for outer UDP checksum error in tunneled packets */
> >  	if ((rx_status1 & BIT(ICE_RX_FLEX_DESC_STATUS1_NAT_S)) &&
> >  	    (rx_status0 & BIT(ICE_RX_FLEX_DESC_STATUS0_XSUM_EUDPE_S)))
> > -		goto checksum_fail;
> > -
> > -	/* If there is an outer header present that might contain a checksum
> > -	 * we need to bump the checksum level by 1 to reflect the fact that
> > -	 * we are indicating we validated the inner checksum.
> > -	 */
> > -	if (decoded.tunnel_type >= ICE_RX_PTYPE_TUNNEL_IP_GRENAT)
> > -		skb->csum_level = 1;
> > +		return ICE_RX_CSUM_FAIL;
> >  
> >  	/* Only report checksum unnecessary for TCP, UDP, or SCTP */
> >  	switch (decoded.inner_prot) {
> >  	case ICE_RX_PTYPE_INNER_PROT_TCP:
> >  	case ICE_RX_PTYPE_INNER_PROT_UDP:
> >  	case ICE_RX_PTYPE_INNER_PROT_SCTP:
> > -		skb->ip_summed = CHECKSUM_UNNECESSARY;
> > -		break;
> > -	default:
> > -		break;
> > +		/* If there is an outer header present that might contain
> > +		 * a checksum we need to bump the checksum level by 1 to reflect
> > +		 * the fact that we have validated the inner checksum.
> > +		 */
> > +		return decoded.tunnel_type >= ICE_RX_PTYPE_TUNNEL_IP_GRENAT ?
> > +		       ICE_RX_CSUM_LVL_1 : ICE_RX_CSUM_LVL_0;
> >  	}
> > -	return;
> >  
> > -checksum_fail:
> > -	ring->vsi->back->hw_csum_rx_error++;
> > +	return ICE_RX_CSUM_NONE;
> > +}
> > +
> > +/**
> > + * ice_rx_csum_into_skb - Indicate in skb if checksum is good
> > + * @ring: the ring we care about
> > + * @skb: skb currently being received and modified
> > + * @rx_desc: the receive descriptor
> > + * @ptype: the packet type decoded by hardware
> > + */
> > +static void
> > +ice_rx_csum_into_skb(struct ice_rx_ring *ring, struct sk_buff *skb,
> > +		     const union ice_32b_rx_flex_desc *rx_desc, u16 ptype)
> > +{
> > +	enum ice_rx_csum_status csum_status;
> > +
> > +	/* check if Rx checksum is enabled */
> > +	if (!(ring->netdev->features & NETIF_F_RXCSUM))
> > +		return;
> > +
> > +	csum_status = ice_get_rx_csum_status(rx_desc, ptype);
> > +	if (csum_status & ICE_RX_CSUM_ERROR)
> > +		ring->vsi->back->hw_csum_rx_error++;
> > +
> > +	skb->ip_summed = ice_rx_csum_ip_summed(csum_status);
> > +	skb->csum_level = ice_rx_csum_lvl(csum_status);
> >  }
> >  
> >  /**
> > @@ -229,7 +262,7 @@ ice_process_skb_fields(struct ice_rx_ring *rx_ring,
> >  	/* modifies the skb - consumes the enet header */
> >  	skb->protocol = eth_type_trans(skb, rx_ring->netdev);
> >  
> > -	ice_rx_csum(rx_ring, skb, rx_desc, ptype);
> > +	ice_rx_csum_into_skb(rx_ring, skb, rx_desc, ptype);
> >  
> >  	if (rx_ring->ptp_rx)
> >  		ice_ptp_rx_hwts_to_skb(rx_ring, rx_desc, skb);
> > -- 
> > 2.41.0
> >