Message-ID: <b00b3064-4a08-b844-3d09-7124f5ab0143@antgroup.com>
Date:   Wed, 15 Mar 2023 20:20:32 +0800
From:   "沈安琪(凛玥)" <amy.saq@...group.com>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org, "Michael S. Tsirkin" <mst@...hat.com>
Cc:     <davem@...emloft.net>, <jasowang@...hat.com>,
        "谈鉴锋" <henry.tjf@...group.com>
Subject: Re: [PATCH v4] net/packet: support mergeable feature of virtio


在 2023/3/13 下午10:05, Willem de Bruijn 写道:
> 沈安琪(凛玥) wrote:
>> From: Jianfeng Tan <henry.tjf@...group.com>
>>
>> Packet sockets, like tap, can be used as the backend for kernel vhost.
>> In packet sockets, virtio net header size is currently hardcoded to be
>> the size of struct virtio_net_hdr, which is 10 bytes; however, it is not
>> always the case: some virtio features, such as mrg_rxbuf, need virtio
>> net headers to be 12-byte long.
>>
>> Mergeable buffers, as a virtio feature, is worthy of supporting: packets
>> that are larger than one-mbuf size will be dropped in vhost worker's
>> handle_rx if mrg_rxbuf feature is not used, but large packets
>> cannot be avoided and increasing mbuf's size is not economical.
>>
>> With this virtio feature enabled by virtio-user, packet sockets with
>> hardcoded 10-byte virtio net header will parse mac head incorrectly in
>> packet_snd by taking the last two bytes of virtio net header as part of
>> mac header.
>> This incorrect mac header parsing will cause packet to be dropped due to
>> invalid ether head checking in later under-layer device packet receiving.
>>
>> By adding extra field vnet_hdr_sz with utilizing holes in struct
>> packet_sock to record currently used virtio net header size and supporting
>> extra sockopt PACKET_VNET_HDR_SZ to set specified vnet_hdr_sz, packet
>> sockets can know the exact length of virtio net header that virtio user
>> gives.
>> In packet_snd, tpacket_snd and packet_recvmsg, instead of using
>> hardcoded virtio net header size, it can get the exact vnet_hdr_sz from
>> corresponding packet_sock, and parse mac header correctly based on this
>> information to avoid the packets being mistakenly dropped.
>>
>> Signed-off-by: Jianfeng Tan <henry.tjf@...group.com>
>> Co-developed-by: Anqi Shen <amy.saq@...group.com>
>> Signed-off-by: Anqi Shen <amy.saq@...group.com>
>> ---
>>
>> V3 -> V4:
>> * read po->vnet_hdr_sz once during vnet_hdr_sz and use vnet_hdr_sz locally
>> to avoid race condition;
>> * modify how to check non-zero po->vnet_hdr_sz;
>> * separate vnet_hdr_sz as a u8 field in struct packet_sock instead of 8-bit
>> in an int field.
>>
>>   include/uapi/linux/if_packet.h |  1 +
>>   net/packet/af_packet.c         | 87 +++++++++++++++++++++++++++---------------
>>   net/packet/diag.c              |  2 +-
>>   net/packet/internal.h          |  2 +-
>>   4 files changed, 59 insertions(+), 33 deletions(-)
>>
>> diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
>> index 78c981d..9efc423 100644
>> --- a/include/uapi/linux/if_packet.h
>> +++ b/include/uapi/linux/if_packet.h
>> @@ -59,6 +59,7 @@ struct sockaddr_ll {
>>   #define PACKET_ROLLOVER_STATS		21
>>   #define PACKET_FANOUT_DATA		22
>>   #define PACKET_IGNORE_OUTGOING		23
>> +#define PACKET_VNET_HDR_SZ		24
>>   
>>   #define PACKET_FANOUT_HASH		0
>>   #define PACKET_FANOUT_LB		1
>> diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
>> index 8ffb19c..06b9893 100644
>> --- a/net/packet/af_packet.c
>> +++ b/net/packet/af_packet.c
>> @@ -2092,18 +2092,18 @@ static unsigned int run_filter(struct sk_buff *skb,
>>   }
>>   
>>   static int packet_rcv_vnet(struct msghdr *msg, const struct sk_buff *skb,
>> -			   size_t *len)
>> +			   size_t *len, int vnet_hdr_sz)
>>   {
>> -	struct virtio_net_hdr vnet_hdr;
>> +	struct virtio_net_hdr_mrg_rxbuf vnet_hdr = { .num_buffers = 0 };
>>   
>> -	if (*len < sizeof(vnet_hdr))
>> +	if (*len < vnet_hdr_sz)
>>   		return -EINVAL;
>> -	*len -= sizeof(vnet_hdr);
>> +	*len -= vnet_hdr_sz;
>>   
>> -	if (virtio_net_hdr_from_skb(skb, &vnet_hdr, vio_le(), true, 0))
>> +	if (virtio_net_hdr_from_skb(skb, (struct virtio_net_hdr *)&vnet_hdr, vio_le(), true, 0))
>>   		return -EINVAL;
>>   
>> -	return memcpy_to_msg(msg, (void *)&vnet_hdr, sizeof(vnet_hdr));
>> +	return memcpy_to_msg(msg, (void *)&vnet_hdr, vnet_hdr_sz);
>>   }
>>   
>>   /*
>> @@ -2253,6 +2253,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>>   	bool is_drop_n_account = false;
>>   	unsigned int slot_id = 0;
>>   	bool do_vnet = false;
>> +	int vnet_hdr_sz;
>>   
>>   	/* struct tpacket{2,3}_hdr is aligned to a multiple of TPACKET_ALIGNMENT.
>>   	 * We may add members to them until current aligned size without forcing
>> @@ -2310,8 +2311,9 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>>   		netoff = TPACKET_ALIGN(po->tp_hdrlen +
>>   				       (maclen < 16 ? 16 : maclen)) +
>>   				       po->tp_reserve;
>> -		if (po->has_vnet_hdr) {
>> -			netoff += sizeof(struct virtio_net_hdr);
>> +		vnet_hdr_sz = po->vnet_hdr_sz;
>> +		if (vnet_hdr_sz) {
>> +			netoff += vnet_hdr_sz;
>>   			do_vnet = true;
>>   		}
>>   		macoff = netoff - maclen;
>> @@ -2552,16 +2554,27 @@ static int __packet_snd_vnet_parse(struct virtio_net_hdr *vnet_hdr, size_t len)
>>   }
>>   
>>   static int packet_snd_vnet_parse(struct msghdr *msg, size_t *len,
>> -				 struct virtio_net_hdr *vnet_hdr)
>> +				 struct virtio_net_hdr *vnet_hdr, int vnet_hdr_sz)
>>   {
>> -	if (*len < sizeof(*vnet_hdr))
>> +	int ret;
>> +
>> +	if (*len < vnet_hdr_sz)
>>   		return -EINVAL;
>> -	*len -= sizeof(*vnet_hdr);
>> +	*len -= vnet_hdr_sz;
>>   
>>   	if (!copy_from_iter_full(vnet_hdr, sizeof(*vnet_hdr), &msg->msg_iter))
>>   		return -EFAULT;
>>   
>> -	return __packet_snd_vnet_parse(vnet_hdr, *len);
>> +	ret = __packet_snd_vnet_parse(vnet_hdr, *len);
>> +
> nit: please drop the whitespace line
>
>> +	if (ret)
>> +		return ret;
>> +
>> +	/* move iter to point to the start of mac header */
>> +	if (vnet_hdr_sz != sizeof(struct virtio_net_hdr))
>> +		iov_iter_advance(&msg->msg_iter, vnet_hdr_sz - sizeof(struct virtio_net_hdr));
>> +
>> +	return 0;
>>   }
>>   
>>   static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
>> @@ -2730,6 +2743,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>>   	int status = TP_STATUS_AVAILABLE;
>>   	int hlen, tlen, copylen = 0;
>>   	long timeo = 0;
>> +	int vnet_hdr_sz = po->vnet_hdr_sz;
> nit: order variables longest to shortest ("reverse christmas tree")
>>   
>>   	mutex_lock(&po->pg_vec_lock);
>>   
>> @@ -2780,7 +2794,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>>   	size_max = po->tx_ring.frame_size
>>   		- (po->tp_hdrlen - sizeof(struct sockaddr_ll));
>>   
>> -	if ((size_max > dev->mtu + reserve + VLAN_HLEN) && !po->has_vnet_hdr)
>> +	if ((size_max > dev->mtu + reserve + VLAN_HLEN) && !vnet_hdr_sz)
>>   		size_max = dev->mtu + reserve + VLAN_HLEN;
>>   
>>   	reinit_completion(&po->skb_completion);
>> @@ -2809,10 +2823,10 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>>   		status = TP_STATUS_SEND_REQUEST;
>>   		hlen = LL_RESERVED_SPACE(dev);
>>   		tlen = dev->needed_tailroom;
>> -		if (po->has_vnet_hdr) {
>> +		if (vnet_hdr_sz) {
>>   			vnet_hdr = data;
>> -			data += sizeof(*vnet_hdr);
>> -			tp_len -= sizeof(*vnet_hdr);
>> +			data += vnet_hdr_sz;
>> +			tp_len -= vnet_hdr_sz;
>>   			if (tp_len < 0 ||
>>   			    __packet_snd_vnet_parse(vnet_hdr, tp_len)) {
>>   				tp_len = -EINVAL;
>> @@ -2837,7 +2851,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>>   					  addr, hlen, copylen, &sockc);
>>   		if (likely(tp_len >= 0) &&
>>   		    tp_len > dev->mtu + reserve &&
>> -		    !po->has_vnet_hdr &&
>> +		    !vnet_hdr_sz &&
>>   		    !packet_extra_vlan_len_allowed(dev, skb))
>>   			tp_len = -EMSGSIZE;
>>   
>> @@ -2856,7 +2870,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
>>   			}
>>   		}
>>   
>> -		if (po->has_vnet_hdr) {
>> +		if (vnet_hdr_sz) {
>>   			if (virtio_net_hdr_to_skb(skb, vnet_hdr, vio_le())) {
>>   				tp_len = -EINVAL;
>>   				goto tpacket_error;
>> @@ -2946,7 +2960,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>>   	struct virtio_net_hdr vnet_hdr = { 0 };
>>   	int offset = 0;
>>   	struct packet_sock *po = pkt_sk(sk);
>> -	bool has_vnet_hdr = false;
>> +	int vnet_hdr_sz = po->vnet_hdr_sz;
>>   	int hlen, tlen, linear;
>>   	int extra_len = 0;
>>   
>> @@ -2990,11 +3004,11 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>>   
>>   	if (sock->type == SOCK_RAW)
>>   		reserve = dev->hard_header_len;
>> -	if (po->has_vnet_hdr) {
>> -		err = packet_snd_vnet_parse(msg, &len, &vnet_hdr);
>> +
> nit: drop extra whitespace line
>
>> +	if (vnet_hdr_sz) {
>> +		err = packet_snd_vnet_parse(msg, &len, &vnet_hdr, vnet_hdr_sz);
>>   		if (err)
>>   			goto out_unlock;
>> -		has_vnet_hdr = true;
>>   	}
>>   
>>   	if (unlikely(sock_flag(sk, SOCK_NOFCS))) {
>> @@ -3064,11 +3078,11 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
>>   
>>   	packet_parse_headers(skb, sock);
>>   
>> -	if (has_vnet_hdr) {
>> +	if (vnet_hdr_sz) {
>>   		err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le());
>>   		if (err)
>>   			goto out_free;
>> -		len += sizeof(vnet_hdr);
>> +		len += vnet_hdr_sz;
>>   		virtio_net_hdr_set_proto(skb, &vnet_hdr);
>>   	}
>>   
>> @@ -3410,7 +3424,7 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>>   	struct sock *sk = sock->sk;
>>   	struct sk_buff *skb;
>>   	int copied, err;
>> -	int vnet_hdr_len = 0;
>> +	int vnet_hdr_len = pkt_sk(sk)->vnet_hdr_sz;
>>   	unsigned int origlen = 0;
>>   
>>   	err = -EINVAL;
>> @@ -3451,11 +3465,10 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>>   
>>   	packet_rcv_try_clear_pressure(pkt_sk(sk));
>>   
>> -	if (pkt_sk(sk)->has_vnet_hdr) {
>> -		err = packet_rcv_vnet(msg, skb, &len);
>> +	if (vnet_hdr_len) {
>> +		err = packet_rcv_vnet(msg, skb, &len, vnet_hdr_len);
>>   		if (err)
>>   			goto out_free;
>> -		vnet_hdr_len = sizeof(struct virtio_net_hdr);
>>   	}
>>   
>>   	/* You lose any data beyond the buffer you gave. If it worries
>> @@ -3921,8 +3934,9 @@ static void packet_flush_mclist(struct sock *sk)
>>   		return 0;
>>   	}
>>   	case PACKET_VNET_HDR:
>> +	case PACKET_VNET_HDR_SZ:
>>   	{
>> -		int val;
>> +		int val, hdr_len;
>>   
>>   		if (sock->type != SOCK_RAW)
>>   			return -EINVAL;
>> @@ -3931,11 +3945,19 @@ static void packet_flush_mclist(struct sock *sk)
>>   		if (copy_from_sockptr(&val, optval, sizeof(val)))
>>   			return -EFAULT;
>>   
>> +		hdr_len = val ? sizeof(struct virtio_net_hdr) : 0;
>> +		if (optname == PACKET_VNET_HDR_SZ) {
>> +			if (val && val != sizeof(struct virtio_net_hdr) &&
>> +			    val != sizeof(struct virtio_net_hdr_mrg_rxbuf))
>> +				return -EINVAL;
>> +			hdr_len = val;
>> +		}
>> +
>>   		lock_sock(sk);
>>   		if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {
>>   			ret = -EBUSY;
>>   		} else {
>> -			po->has_vnet_hdr = !!val;
>> +			po->vnet_hdr_sz = hdr_len;
>>   			ret = 0;
>>   		}
>>   		release_sock(sk);
>> @@ -4068,7 +4090,10 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
>>   		val = po->origdev;
>>   		break;
>>   	case PACKET_VNET_HDR:
>> -		val = po->has_vnet_hdr;
>> +		val = !!po->vnet_hdr_sz;
>> +		break;
>> +	case PACKET_VNET_HDR_SZ:
>> +		val = po->vnet_hdr_sz;
>>   		break;
>>   	case PACKET_VERSION:
>>   		val = po->tp_version;
>> diff --git a/net/packet/diag.c b/net/packet/diag.c
>> index 07812ae..dfec603 100644
>> --- a/net/packet/diag.c
>> +++ b/net/packet/diag.c
>> @@ -27,7 +27,7 @@ static int pdiag_put_info(const struct packet_sock *po, struct sk_buff *nlskb)
>>   		pinfo.pdi_flags |= PDI_AUXDATA;
>>   	if (po->origdev)
>>   		pinfo.pdi_flags |= PDI_ORIGDEV;
>> -	if (po->has_vnet_hdr)
>> +	if (po->vnet_hdr_sz)
>>   		pinfo.pdi_flags |= PDI_VNETHDR;
>>   	if (po->tp_loss)
>>   		pinfo.pdi_flags |= PDI_LOSS;
>> diff --git a/net/packet/internal.h b/net/packet/internal.h
>> index 48af35b..154c6bb 100644
>> --- a/net/packet/internal.h
>> +++ b/net/packet/internal.h
>> @@ -119,9 +119,9 @@ struct packet_sock {
>>   	unsigned int		running;	/* bind_lock must be held */
>>   	unsigned int		auxdata:1,	/* writer must hold sock lock */
>>   				origdev:1,
>> -				has_vnet_hdr:1,
>>   				tp_loss:1,
>>   				tp_tx_has_off:1;
>> +	u8			vnet_hdr_sz;
>>   	int			pressure;
>>   	int			ifindex;	/* bound device		*/
>>   	__be16			num;
>> -- 
>> 1.8.3.1
>>

Thanks for the comments! We will address them in the next version of patch.

Besides 1) adding READ_ONCE macro to local vnet_hdr_sz; 2) fixing some 
coding format; 3) nice to have some performance test, is there any other 
suggestion on this version? Again, thanks for all the advice : )

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