Subject: Re: [PATCH net, 3/3] net: mana: Fix oversized sge0 for GSO packets

From: Simon Horman <[email-masked]>
Date: Fri, 29 Sep 2023 10:56:40 +0200

On Sat, Sep 23, 2023 at 06:31:47PM -0700, Haiyang Zhang wrote:
> Handle the case when GSO SKB linear length is too large.
> 
> MANA NIC requires GSO packets to put only the header part to SGE0,
> otherwise the TX queue may stop at the HW level.
> 
> So, use 2 SGEs for the skb linear part which contains more than the
> packet header.
> 
> Fixes: ca9c54d2d6a5 ("net: mana: Add a driver for Microsoft Azure Network Adapter (MANA)")
> Signed-off-by: Haiyang Zhang <[email-masked]>

Hi Haiyang Zhang,

thanks for your patch.
Please find some feedback inline.

> ---
>  drivers/net/ethernet/microsoft/mana/mana_en.c | 186 ++++++++++++------
>  include/net/mana/mana.h                       |   5 +-
>  2 files changed, 134 insertions(+), 57 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
> index 86e724c3eb89..0a3879163b56 100644
> --- a/drivers/net/ethernet/microsoft/mana/mana_en.c
> +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
> @@ -91,63 +91,136 @@ static unsigned int mana_checksum_info(struct sk_buff *skb)
>  	return 0;
>  }
>  
> +static inline void mana_add_sge(struct mana_tx_package *tp,
> +				struct mana_skb_head *ash, int sg_i,
> +				dma_addr_t da, int sge_len, u32 gpa_mkey)

Please don't use inline for code in .c files unless there
is a demonstrable reason to do so: in general, the compiler should be
left to inline code as it sees fit.

> +{
> +	ash->dma_handle[sg_i] = da;
> +	ash->size[sg_i] = sge_len;
> +
> +	tp->wqe_req.sgl[sg_i].address = da;
> +	tp->wqe_req.sgl[sg_i].mem_key = gpa_mkey;
> +	tp->wqe_req.sgl[sg_i].size = sge_len;
> +}
> +
>  static int mana_map_skb(struct sk_buff *skb, struct mana_port_context *apc,
> -			struct mana_tx_package *tp)
> +			struct mana_tx_package *tp, int gso_hs)
>  {
>  	struct mana_skb_head *ash = (struct mana_skb_head *)skb->head;
> +	int hsg = 1; /* num of SGEs of linear part */
>  	struct gdma_dev *gd = apc->ac->gdma_dev;
> +	int skb_hlen = skb_headlen(skb);
> +	int sge0_len, sge1_len = 0;
>  	struct gdma_context *gc;
>  	struct device *dev;
>  	skb_frag_t *frag;
>  	dma_addr_t da;
> +	int sg_i;
>  	int i;
>  
>  	gc = gd->gdma_context;
>  	dev = gc->dev;
> -	da = dma_map_single(dev, skb->data, skb_headlen(skb), DMA_TO_DEVICE);
>  
> +	if (gso_hs && gso_hs < skb_hlen) {
> +		sge0_len = gso_hs;
> +		sge1_len = skb_hlen - gso_hs;
> +	} else {
> +		sge0_len = skb_hlen;
> +	}
> +
> +	da = dma_map_single(dev, skb->data, sge0_len, DMA_TO_DEVICE);
>  	if (dma_mapping_error(dev, da))
>  		return -ENOMEM;
>  
> -	ash->dma_handle[0] = da;
> -	ash->size[0] = skb_headlen(skb);
> +	mana_add_sge(tp, ash, 0, da, sge0_len, gd->gpa_mkey);
>  
> -	tp->wqe_req.sgl[0].address = ash->dma_handle[0];
> -	tp->wqe_req.sgl[0].mem_key = gd->gpa_mkey;
> -	tp->wqe_req.sgl[0].size = ash->size[0];
> +	if (sge1_len) {
> +		sg_i = 1;
> +		da = dma_map_single(dev, skb->data + sge0_len, sge1_len,
> +				    DMA_TO_DEVICE);
> +		if (dma_mapping_error(dev, da))
> +			goto frag_err;
> +
> +		mana_add_sge(tp, ash, sg_i, da, sge1_len, gd->gpa_mkey);
> +		hsg = 2;
> +	}
>  
>  	for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
> +		sg_i = hsg + i;
> +
>  		frag = &skb_shinfo(skb)->frags[i];
>  		da = skb_frag_dma_map(dev, frag, 0, skb_frag_size(frag),
>  				      DMA_TO_DEVICE);
> -
>  		if (dma_mapping_error(dev, da))
>  			goto frag_err;
>  
> -		ash->dma_handle[i + 1] = da;
> -		ash->size[i + 1] = skb_frag_size(frag);
> -
> -		tp->wqe_req.sgl[i + 1].address = ash->dma_handle[i + 1];
> -		tp->wqe_req.sgl[i + 1].mem_key = gd->gpa_mkey;
> -		tp->wqe_req.sgl[i + 1].size = ash->size[i + 1];
> +		mana_add_sge(tp, ash, sg_i, da, skb_frag_size(frag),
> +			     gd->gpa_mkey);
>  	}
>  
>  	return 0;
>  
>  frag_err:
> -	for (i = i - 1; i >= 0; i--)
> -		dma_unmap_page(dev, ash->dma_handle[i + 1], ash->size[i + 1],
> +	for (i = sg_i - 1; i >= hsg; i--)
> +		dma_unmap_page(dev, ash->dma_handle[i], ash->size[i],
>  			       DMA_TO_DEVICE);
>  
> -	dma_unmap_single(dev, ash->dma_handle[0], ash->size[0], DMA_TO_DEVICE);
> +	for (i = hsg - 1; i >= 0; i--)
> +		dma_unmap_single(dev, ash->dma_handle[i], ash->size[i],
> +				 DMA_TO_DEVICE);
>  
>  	return -ENOMEM;
>  }
>  
> +/* Handle the case when GSO SKB linear length is too large.
> + * MANA NIC requires GSO packets to put only the packet header to SGE0.
> + * So, we need 2 SGEs for the skb linear part which contains more than the
> + * header.
> + */
> +static inline int mana_fix_skb_head(struct net_device *ndev,
> +				    struct sk_buff *skb, int gso_hs,
> +				    u32 *num_sge)
> +{
> +	int skb_hlen = skb_headlen(skb);
> +
> +	if (gso_hs < skb_hlen) {
> +		*num_sge = 2 + skb_shinfo(skb)->nr_frags;
> +	} else if (gso_hs > skb_hlen) {
> +		if (net_ratelimit())
> +			netdev_err(ndev,
> +				   "TX nonlinear head: hs:%d, skb_hlen:%d\n",
> +				   gso_hs, skb_hlen);
> +
> +		return -EINVAL;
> +	}
> +
> +	return 0;

nit: I think it would be slightly nicer if the num_sge parameter of this
function was removed and it returned negative values on error (already
the case) and positive values, representing the number f segments, on success.

> +}
> +
> +/* Get the GSO packet's header size */
> +static inline int mana_get_gso_hs(struct sk_buff *skb)
> +{
> +	int gso_hs;
> +
> +	if (skb->encapsulation) {
> +		gso_hs = skb_inner_tcp_all_headers(skb);
> +	} else {
> +		if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) {
> +			gso_hs = skb_transport_offset(skb) +
> +				 sizeof(struct udphdr);
> +		} else {
> +			gso_hs = skb_tcp_all_headers(skb);
> +		}
> +	}
> +
> +	return gso_hs;
> +}
> +
>  netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  {
>  	enum mana_tx_pkt_format pkt_fmt = MANA_SHORT_PKT_FMT;
>  	struct mana_port_context *apc = netdev_priv(ndev);
> +	int gso_hs = 0; /* zero for non-GSO pkts */
>  	u16 txq_idx = skb_get_queue_mapping(skb);
>  	struct gdma_dev *gd = apc->ac->gdma_dev;
>  	bool ipv4 = false, ipv6 = false;
> @@ -159,7 +232,6 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  	struct mana_txq *txq;
>  	struct mana_cq *cq;
>  	int err, len;
> -	u16 ihs;
>  
>  	if (unlikely(!apc->port_is_up))
>  		goto tx_drop;
> @@ -209,19 +281,6 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  	pkg.wqe_req.client_data_unit = 0;
>  
>  	pkg.wqe_req.num_sge = 1 + skb_shinfo(skb)->nr_frags;
> -	WARN_ON_ONCE(pkg.wqe_req.num_sge > MAX_TX_WQE_SGL_ENTRIES);
> -
> -	if (pkg.wqe_req.num_sge <= ARRAY_SIZE(pkg.sgl_array)) {
> -		pkg.wqe_req.sgl = pkg.sgl_array;
> -	} else {
> -		pkg.sgl_ptr = kmalloc_array(pkg.wqe_req.num_sge,
> -					    sizeof(struct gdma_sge),
> -					    GFP_ATOMIC);
> -		if (!pkg.sgl_ptr)
> -			goto tx_drop_count;
> -
> -		pkg.wqe_req.sgl = pkg.sgl_ptr;
> -	}

It is unclear to me why this logic has moved from here to further
down in this function. Is it to avoid some cases where
alloation has to be unwond on error (when mana_fix_skb_head() fails) ?
If so, this feels more like an optimisation than a fix.

>  
>  	if (skb->protocol == htons(ETH_P_IP))
>  		ipv4 = true;
> @@ -229,6 +288,23 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  		ipv6 = true;
>  
>  	if (skb_is_gso(skb)) {
> +		gso_hs = mana_get_gso_hs(skb);
> +
> +		if (mana_fix_skb_head(ndev, skb, gso_hs, &pkg.wqe_req.num_sge))
> +			goto tx_drop_count;
> +
> +		if (skb->encapsulation) {
> +			u64_stats_update_begin(&tx_stats->syncp);
> +			tx_stats->tso_inner_packets++;
> +			tx_stats->tso_inner_bytes += skb->len - gso_hs;
> +			u64_stats_update_end(&tx_stats->syncp);
> +		} else {
> +			u64_stats_update_begin(&tx_stats->syncp);
> +			tx_stats->tso_packets++;
> +			tx_stats->tso_bytes += skb->len - gso_hs;
> +			u64_stats_update_end(&tx_stats->syncp);
> +		}

nit: I wonder if this could be slightly more succinctly written as:

		u64_stats_update_begin(&tx_stats->syncp);
		if (skb->encapsulation) {
			tx_stats->tso_inner_packets++;
			tx_stats->tso_inner_bytes += skb->len - gso_hs;
		} else {
			tx_stats->tso_packets++;
			tx_stats->tso_bytes += skb->len - gso_hs;
		}
		u64_stats_update_end(&tx_stats->syncp);

Also, it is unclear to me why the stats logic is moved here from
futher down in the same block. It feels more like a clean-up than a fix
(as, btw, is my suggestion immediately above).

> +
>  		pkg.tx_oob.s_oob.is_outer_ipv4 = ipv4;
>  		pkg.tx_oob.s_oob.is_outer_ipv6 = ipv6;
>  
> @@ -252,26 +328,6 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  						 &ipv6_hdr(skb)->daddr, 0,
>  						 IPPROTO_TCP, 0);
>  		}
> -
> -		if (skb->encapsulation) {
> -			ihs = skb_inner_tcp_all_headers(skb);
> -			u64_stats_update_begin(&tx_stats->syncp);
> -			tx_stats->tso_inner_packets++;
> -			tx_stats->tso_inner_bytes += skb->len - ihs;
> -			u64_stats_update_end(&tx_stats->syncp);
> -		} else {
> -			if (skb_shinfo(skb)->gso_type & SKB_GSO_UDP_L4) {
> -				ihs = skb_transport_offset(skb) + sizeof(struct udphdr);
> -			} else {
> -				ihs = skb_tcp_all_headers(skb);
> -			}
> -
> -			u64_stats_update_begin(&tx_stats->syncp);
> -			tx_stats->tso_packets++;
> -			tx_stats->tso_bytes += skb->len - ihs;
> -			u64_stats_update_end(&tx_stats->syncp);
> -		}
> -
>  	} else if (skb->ip_summed == CHECKSUM_PARTIAL) {
>  		csum_type = mana_checksum_info(skb);
>  
> @@ -294,11 +350,25 @@ netdev_tx_t mana_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  		} else {
>  			/* Can't do offload of this type of checksum */
>  			if (skb_checksum_help(skb))
> -				goto free_sgl_ptr;
> +				goto tx_drop_count;
>  		}
>  	}
>  
> -	if (mana_map_skb(skb, apc, &pkg)) {
> +	WARN_ON_ONCE(pkg.wqe_req.num_sge > MAX_TX_WQE_SGL_ENTRIES);
> +
> +	if (pkg.wqe_req.num_sge <= ARRAY_SIZE(pkg.sgl_array)) {
> +		pkg.wqe_req.sgl = pkg.sgl_array;
> +	} else {
> +		pkg.sgl_ptr = kmalloc_array(pkg.wqe_req.num_sge,
> +					    sizeof(struct gdma_sge),
> +					    GFP_ATOMIC);
> +		if (!pkg.sgl_ptr)
> +			goto tx_drop_count;
> +
> +		pkg.wqe_req.sgl = pkg.sgl_ptr;
> +	}
> +
> +	if (mana_map_skb(skb, apc, &pkg, gso_hs)) {
>  		u64_stats_update_begin(&tx_stats->syncp);
>  		tx_stats->mana_map_err++;
>  		u64_stats_update_end(&tx_stats->syncp);
> @@ -1255,12 +1325,18 @@ static void mana_unmap_skb(struct sk_buff *skb, struct mana_port_context *apc)
>  {
>  	struct mana_skb_head *ash = (struct mana_skb_head *)skb->head;
>  	struct gdma_context *gc = apc->ac->gdma_dev->gdma_context;
> +	int hsg = 1; /* num of SGEs of linear part */
>  	struct device *dev = gc->dev;
>  	int i;
>  
> -	dma_unmap_single(dev, ash->dma_handle[0], ash->size[0], DMA_TO_DEVICE);
> +	if (skb_is_gso(skb) && skb_headlen(skb) > ash->size[0])
> +		hsg = 2;

nit: Maybe this is nicer?

	/* num of SGEs of linear part */
	hsg = (skb_is_gso(skb) && skb_headlen(skb) > ash->size[0]) ? 2 : 1;

> +
> +	for (i = 0; i < hsg; i++)
> +		dma_unmap_single(dev, ash->dma_handle[i], ash->size[i],
> +				 DMA_TO_DEVICE);
>  
> -	for (i = 1; i < skb_shinfo(skb)->nr_frags + 1; i++)
> +	for (i = hsg; i < skb_shinfo(skb)->nr_frags + hsg; i++)
>  		dma_unmap_page(dev, ash->dma_handle[i], ash->size[i],
>  			       DMA_TO_DEVICE);
>  }
> diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
> index 9f70b4332238..4d43adf18606 100644
> --- a/include/net/mana/mana.h
> +++ b/include/net/mana/mana.h
> @@ -103,9 +103,10 @@ struct mana_txq {
>  
>  /* skb data and frags dma mappings */
>  struct mana_skb_head {
> -	dma_addr_t dma_handle[MAX_SKB_FRAGS + 1];
> +	/* GSO pkts may have 2 SGEs for the linear part*/
> +	dma_addr_t dma_handle[MAX_SKB_FRAGS + 2];
>  
> -	u32 size[MAX_SKB_FRAGS + 1];
> +	u32 size[MAX_SKB_FRAGS + 2];
>  };
>  
>  #define MANA_HEADROOM sizeof(struct mana_skb_head)
> -- 
> 2.25.1
> 
>