Re: [PATCH net-next] virtio-net: realign page_to_skb() after merges

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Aug 02, 2021 at 10:57:29AM -0700, Jakub Kicinski wrote:
> We ended up merging two versions of the same patch set:
> 
> commit 8fb7da9e9907 ("virtio_net: get build_skb() buf by data ptr")
> commit 5c37711d9f27 ("virtio-net: fix for unable to handle page fault for address")
> 
> into net, and
> 
> commit 7bf64460e3b2 ("virtio-net: get build_skb() buf by data ptr")
> commit 6c66c147b9a4 ("virtio-net: fix for unable to handle page fault for address")
> 
> into net-next. Redo the merge from commit 126285651b7f ("Merge
> ra.kernel.org:/pub/scm/linux/kernel/git/netdev/net"), so that
> the most recent code remains.
> 
> Acked-by: Michael S. Tsirkin <mst@redhat.com>
> Signed-off-by: Jakub Kicinski <kuba@kernel.org>

And maybe add

Fixes: 126285651b7f ("Merge ra.kernel.org:/pub/scm/linux/kernel/git/netdev/net")

so automated tools have an easier time finding this fixup.

> ---
>  drivers/net/virtio_net.c | 27 ++++++++-------------------
>  1 file changed, 8 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 56c3f8519093..74482a52f076 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -380,7 +380,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  				   struct page *page, unsigned int offset,
>  				   unsigned int len, unsigned int truesize,
>  				   bool hdr_valid, unsigned int metasize,
> -				   bool whole_page)
> +				   unsigned int headroom)
>  {
>  	struct sk_buff *skb;
>  	struct virtio_net_hdr_mrg_rxbuf *hdr;
> @@ -398,28 +398,16 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  	else
>  		hdr_padded_len = sizeof(struct padded_vnet_hdr);
>  
> -	/* If whole_page, there is an offset between the beginning of the
> +	/* If headroom is not 0, there is an offset between the beginning of the
>  	 * data and the allocated space, otherwise the data and the allocated
>  	 * space are aligned.
>  	 *
>  	 * Buffers with headroom use PAGE_SIZE as alloc size, see
>  	 * add_recvbuf_mergeable() + get_mergeable_buf_len()
>  	 */
> -	if (whole_page) {
> -		/* Buffers with whole_page use PAGE_SIZE as alloc size,
> -		 * see add_recvbuf_mergeable() + get_mergeable_buf_len()
> -		 */
> -		truesize = PAGE_SIZE;
> -
> -		/* page maybe head page, so we should get the buf by p, not the
> -		 * page
> -		 */
> -		tailroom = truesize - len - offset_in_page(p);
> -		buf = (char *)((unsigned long)p & PAGE_MASK);
> -	} else {
> -		tailroom = truesize - len;
> -		buf = p;
> -	}
> +	truesize = headroom ? PAGE_SIZE : truesize;
> +	tailroom = truesize - len - headroom;
> +	buf = p - headroom;
>  
>  	len -= hdr_len;
>  	offset += hdr_padded_len;
> @@ -978,7 +966,8 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  				put_page(page);
>  				head_skb = page_to_skb(vi, rq, xdp_page, offset,
>  						       len, PAGE_SIZE, false,
> -						       metasize, true);
> +						       metasize,
> +						       VIRTIO_XDP_HEADROOM);
>  				return head_skb;
>  			}
>  			break;
> @@ -1029,7 +1018,7 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  	rcu_read_unlock();
>  
>  	head_skb = page_to_skb(vi, rq, page, offset, len, truesize, !xdp_prog,
> -			       metasize, !!headroom);
> +			       metasize, headroom);
>  	curr_skb = head_skb;
>  
>  	if (unlikely(!curr_skb))
> -- 
> 2.31.1