netdev - Re: [PATCH net-next 1/8] virtio_net: mergeable xdp: put old page immediately

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <4bd07874-b1ad-336b-b15e-ba56a10182e9@huawei.com>
Date:   Wed, 22 Mar 2023 16:22:18 +0800
From:   Yunsheng Lin <linyunsheng@...wei.com>
To:     Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, <netdev@...r.kernel.org>
CC:     "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        John Fastabend <john.fastabend@...il.com>,
        <virtualization@...ts.linux-foundation.org>, <bpf@...r.kernel.org>
Subject: Re: [PATCH net-next 1/8] virtio_net: mergeable xdp: put old page
 immediately

On 2023/3/22 11:03, Xuan Zhuo wrote:
> In the xdp implementation of virtio-net mergeable, it always checks
> whether two page is used and a page is selected to release. This is
> complicated for the processing of action, and be careful.
> 
> In the entire process, we have such principles:
> * If xdp_page is used (PASS, TX, Redirect), then we release the old
>   page.
> * If it is a drop case, we will release two. The old page obtained from
>   buf is release inside err_xdp, and xdp_page needs be relased by us.
> 
> But in fact, when we allocate a new page, we can release the old page
> immediately. Then just one is using, we just need to release the new
> page for drop case. On the drop path, err_xdp will release the variable
> "page", so we only need to let "page" point to the new xdp_page in
> advance.
> 
> Signed-off-by: Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
> ---
>  drivers/net/virtio_net.c | 15 ++++++---------
>  1 file changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index e2560b6f7980..4d2bf1ce0730 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -1245,6 +1245,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			if (!xdp_page)
>  				goto err_xdp;
>  			offset = VIRTIO_XDP_HEADROOM;
> +
> +			put_page(page);

the error handling of xdp_linearize_page() does not seems self contained.
Does it not seem better：
1. if xdp_linearize_page() succesed, call put_page() for first buffer just
   as put_page() is call for other buffer
2. or call virtqueue_get_buf() and put_page() for all the buffer of the packet
   so the error handling is not needed outside the virtqueue_get_buf().

In that case, it seems we can just do below without xdp_page:
page = xdp_linearize_page(rq, num_buf, page, ...);


> +			page = xdp_page;
>  		} else if (unlikely(headroom < virtnet_get_headroom(vi))) {
>  			xdp_room = SKB_DATA_ALIGN(VIRTIO_XDP_HEADROOM +
>  						  sizeof(struct skb_shared_info));
> @@ -1259,6 +1262,9 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			       page_address(page) + offset, len);
>  			frame_sz = PAGE_SIZE;
>  			offset = VIRTIO_XDP_HEADROOM;
> +
> +			put_page(page);
> +			page = xdp_page;

It seems we can limit the scope of xdp_page in this "else if" block.

>  		} else {
>  			xdp_page = page;
>  		}

It seems the above else block is not needed anymore.

> @@ -1278,8 +1284,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			if (unlikely(!head_skb))
>  				goto err_xdp_frags;
>  
> -			if (unlikely(xdp_page != page))
> -				put_page(page);
>  			rcu_read_unlock();
>  			return head_skb;
>  		case XDP_TX:
> @@ -1297,8 +1301,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  				goto err_xdp_frags;
>  			}
>  			*xdp_xmit |= VIRTIO_XDP_TX;
> -			if (unlikely(xdp_page != page))
> -				put_page(page);
>  			rcu_read_unlock();
>  			goto xdp_xmit;
>  		case XDP_REDIRECT:
> @@ -1307,8 +1309,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			if (err)
>  				goto err_xdp_frags;
>  			*xdp_xmit |= VIRTIO_XDP_REDIR;
> -			if (unlikely(xdp_page != page))
> -				put_page(page);
>  			rcu_read_unlock();
>  			goto xdp_xmit;
>  		default:
> @@ -1321,9 +1321,6 @@ static struct sk_buff *receive_mergeable(struct net_device *dev,
>  			goto err_xdp_frags;
>  		}
>  err_xdp_frags:
> -		if (unlikely(xdp_page != page))
> -			__free_pages(xdp_page, 0);

It seems __free_pages() and put_page() is used interchangeably here.
Perhaps using __free_pages() have performance reason? As the comment below:

https://elixir.bootlin.com/linux/v6.3-rc3/source/net/core/page_pool.c#L500

> -
>  		if (xdp_buff_has_frags(&xdp)) {
>  			shinfo = xdp_get_shared_info_from_buff(&xdp);
>  			for (i = 0; i < shinfo->nr_frags; i++) {
>