Received-SPF: pass (google.com: domain of linux-kernel+bounces-8833-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.48.161 as permitted sender) client-ip=147.75.48.161;
Date: Thu, 21 Dec 2023 18:16:48 +0100
From: Simon Horman <horms@kernel.org>
To: Mina Almasry <almasrymina@google.com>
Cc: linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
	kvm@vger.kernel.org, virtualization@lists.linux.dev,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Stefano Garzarella <sgarzare@redhat.com>,
	David Howells <dhowells@redhat.com>,
	Jason Gunthorpe <jgg@nvidia.com>,
	Christian =?utf-8?B?S8O2bmln?= <christian.koenig@amd.com>,
	Shakeel Butt <shakeelb@google.com>,
	Yunsheng Lin <linyunsheng@huawei.com>,
	Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Subject: Re: [PATCH net-next v3 3/3] net: add netmem_ref to skb_frag_t
Message-ID: <20231221171648.GC1056991@kernel.org>
References: <20231220214505.2303297-1-almasrymina@google.com>
 <20231220214505.2303297-4-almasrymina@google.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20231220214505.2303297-4-almasrymina@google.com>

On Wed, Dec 20, 2023 at 01:45:02PM -0800, Mina Almasry wrote:
> Use netmem_ref instead of page in skb_frag_t. Currently netmem_ref
> is always a struct page underneath, but the abstraction allows efforts
> to add support for skb frags not backed by pages.
> 
> There is unfortunately 1 instance where the skb_frag_t is assumed to be
> a bio_vec in kcm. For this case, add a debug assert that the skb frag is
> indeed backed by a page, and do a cast.
> 
> Add skb[_frag]_fill_netmem_*() and skb_add_rx_frag_netmem() helpers so
> that the API can be used to create netmem skbs.
> 
> Signed-off-by: Mina Almasry <almasrymina@google.com>

...

> diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
> index 65d1f6755f98..3180a54b2c68 100644
> --- a/net/kcm/kcmsock.c
> +++ b/net/kcm/kcmsock.c
> @@ -636,9 +636,15 @@ static int kcm_write_msgs(struct kcm_sock *kcm)
>  		for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
>  			msize += skb_shinfo(skb)->frags[i].bv_len;
>  
> +		/* The cast to struct bio_vec* here assumes the frags are
> +		 * struct page based. WARN if there is no page in this skb.
> +		 */
> +		DEBUG_NET_WARN_ON_ONCE(
> +			!skb_frag_page(&skb_shinfo(skb)->frags[0]));
> +
>  		iov_iter_bvec(&msg.msg_iter, ITER_SOURCE,
> -			      skb_shinfo(skb)->frags, skb_shinfo(skb)->nr_frags,
> -			      msize);
> +			      (const struct bio_vec *)skb_shinfo(skb)->frags,
> +			      skb_shinfo(skb)->nr_frags, msize);
>  		iov_iter_advance(&msg.msg_iter, txm->frag_offset);
>  
>  		do {

Hi Mina,

something isn't quite right here.

  ...//kcmsock.c:637:39: error: no member named 'bv_len' in 'struct skb_frag'
  637 |                         msize += skb_shinfo(skb)->frags[i].bv_len;
      |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~ ^

-- 
pw-bot: changes-requested