linux-kernel - Re: [PATCH net-next v6 12/12] net/mlx5e: Add TX support for netmems

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Message-ID: <aFM6r9kFHeTdj-25@mini-arch>
Date: Wed, 18 Jun 2025 15:16:15 -0700
From: Stanislav Fomichev <stfomichev@...il.com>
To: Mark Bloch <mbloch@...dia.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Simon Horman <horms@...nel.org>, saeedm@...dia.com, gal@...dia.com,
	leonro@...dia.com, tariqt@...dia.com,
	Leon Romanovsky <leon@...nel.org>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	Ilias Apalodimas <ilias.apalodimas@...aro.org>,
	Richard Cochran <richardcochran@...il.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Stanislav Fomichev <sdf@...ichev.me>, netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org, linux-kernel@...r.kernel.org,
	bpf@...r.kernel.org, Dragos Tatulea <dtatulea@...dia.com>,
	Mina Almasry <almasrymina@...gle.com>
Subject: Re: [PATCH net-next v6 12/12] net/mlx5e: Add TX support for netmems

On 06/16, Mark Bloch wrote:
> From: Dragos Tatulea <dtatulea@...dia.com>
> 
> Declare netmem TX support in netdev.
> 
> As required, use the netmem aware dma unmapping APIs
> for unmapping netmems in tx completion path.
> 
> Signed-off-by: Dragos Tatulea <dtatulea@...dia.com>
> Reviewed-by: Tariq Toukan <tariqt@...dia.com>
> Reviewed-by: Mina Almasry <almasrymina@...gle.com>
> Signed-off-by: Mark Bloch <mbloch@...dia.com>
> ---
>  drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h | 3 ++-
>  drivers/net/ethernet/mellanox/mlx5/core/en_main.c | 2 ++
>  2 files changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h b/drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h
> index e837c21d3d21..6501252359b0 100644
> --- a/drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h
> +++ b/drivers/net/ethernet/mellanox/mlx5/core/en/txrx.h
> @@ -362,7 +362,8 @@ mlx5e_tx_dma_unmap(struct device *pdev, struct mlx5e_sq_dma *dma)
>  		dma_unmap_single(pdev, dma->addr, dma->size, DMA_TO_DEVICE);
>  		break;
>  	case MLX5E_DMA_MAP_PAGE:
> -		dma_unmap_page(pdev, dma->addr, dma->size, DMA_TO_DEVICE);
> +		netmem_dma_unmap_page_attrs(pdev, dma->addr, dma->size,
> +					    DMA_TO_DEVICE, 0);

For this to work, the dma->addr needs to be 0, so the callers of the
dma_map() need to be adjusted as well, or am I missing something?
There is netmem_dma_unmap_addr_set to handle that, but I don't see
anybody calling it. Do we need to add the following (untested)?

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
index 55a8629f0792..fb6465210aed 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_tx.c
@@ -210,7 +210,9 @@ mlx5e_txwqe_build_dsegs(struct mlx5e_txqsq *sq, struct sk_buff *skb,
 		if (unlikely(dma_mapping_error(sq->pdev, dma_addr)))
 			goto dma_unmap_wqe_err;
 
-		dseg->addr       = cpu_to_be64(dma_addr);
+		dseg->addr = 0;
+		if (!netmem_is_net_iov(skb_frag_netmem(frag)))
+			dseg->addr = cpu_to_be64(dma_addr);
 		dseg->lkey       = sq->mkey_be;
 		dseg->byte_count = cpu_to_be32(fsz);