linux-kernel - Re: [PATCH v3] virtio_net: Fix mismatched buf address when unmapping for small packets

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Message-ID: <20240918105803-mutt-send-email-mst@kernel.org>
Date: Wed, 18 Sep 2024 10:58:23 -0400
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Wenbo Li <liwenbo.martin@...edance.com>
Cc: jasowang@...hat.com, xuanzhuo@...ux.alibaba.com, eperezma@...hat.com,
	davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, virtualization@...ts.linux.dev,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jiahui Cen <cenjiahui@...edance.com>,
	Ying Fang <fangying.tommy@...edance.com>
Subject: Re: [PATCH v3] virtio_net: Fix mismatched buf address when unmapping
 for small packets

On Wed, Sep 18, 2024 at 09:20:05PM +0800, Wenbo Li wrote:
> Currently, the virtio-net driver will perform a pre-dma-mapping for
> small or mergeable RX buffer. But for small packets, a mismatched address
> without VIRTNET_RX_PAD and xdp_headroom is used for unmapping.
> 
> That will result in unsynchronized buffers when SWIOTLB is enabled, for
> example, when running as a TDX guest.
> 
> This patch unifies the address passed to the virtio core into the address of
> the virtnet header and fixes the mismatched buffer address.
> 
> Changes from v2: unify the buf that passed to the virtio core in small
> and merge mode.
> Changes from v1: Use ctx to get xdp_headroom.
> 
> Fixes: 295525e29a5b ("virtio_net: merge dma operations when filling mergeable buffers")
> Signed-off-by: Wenbo Li <liwenbo.martin@...edance.com>
> Signed-off-by: Jiahui Cen <cenjiahui@...edance.com>
> Signed-off-by: Ying Fang <fangying.tommy@...edance.com>

OK but can you please adhere to the kernel coding style?



> ---
>  drivers/net/virtio_net.c | 13 ++++++++++---
>  1 file changed, 10 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 6f4781ec2b36..9446666c84aa 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1804,9 +1804,15 @@ static struct sk_buff *receive_small(struct net_device *dev,
>  				     struct virtnet_rq_stats *stats)
>  {
>  	unsigned int xdp_headroom = (unsigned long)ctx;
> -	struct page *page = virt_to_head_page(buf);
> +	struct page *page;
>  	struct sk_buff *skb;
>  
> +	// We passed the address of virtnet header to virtio-core,
> +	// so truncate the padding.
> +	buf -= VIRTNET_RX_PAD + xdp_headroom;
> +
> +	page = virt_to_head_page(buf);
> +
>  	len -= vi->hdr_len;
>  	u64_stats_add(&stats->bytes, len);
>  
> @@ -2422,8 +2428,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>  	if (unlikely(!buf))
>  		return -ENOMEM;
>  
> -	virtnet_rq_init_one_sg(rq, buf + VIRTNET_RX_PAD + xdp_headroom,
> -			       vi->hdr_len + GOOD_PACKET_LEN);
> +	buf += VIRTNET_RX_PAD + xdp_headroom;
> +
> +	virtnet_rq_init_one_sg(rq, buf, vi->hdr_len + GOOD_PACKET_LEN);
>  
>  	err = virtqueue_add_inbuf_ctx(rq->vq, rq->sg, 1, buf, ctx, gfp);
>  	if (err < 0) {
> -- 
> 2.20.1