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Date: Tue, 28 Feb 2023 10:27:58 +0800
From: "沈安琪(凛玥)" <amy.saq@...group.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>,
netdev@...r.kernel.org
Cc: <mst@...hat.com>, <davem@...emloft.net>, <jasowang@...hat.com>,
"谈鉴锋" <henry.tjf@...group.com>
Subject: Re: [PATCH v2] net/packet: support mergeable feautre of virtio
在 2023/2/28 上午12:31, 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 header to be 12-byte long.
>>
>> Mergeable buffers, as a virtio feature, is worthy to support: packets
>> that 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, 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 as well.
>> This incorrect mac header parsing will cause packet 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 current using 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 hardcode
>> 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>
> net-next is closed
May we still send the revision of this patch and/or keep discussing
during the merge window? We understand that new features will not be
took until the merge window finishes.
>
>> @@ -2311,7 +2312,7 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
>> (maclen < 16 ? 16 : maclen)) +
>> po->tp_reserve;
>> if (po->has_vnet_hdr) {
>> - netoff += sizeof(struct virtio_net_hdr);
>> + netoff += po->vnet_hdr_sz;
>> do_vnet = true;
>> }
>> macoff = netoff - maclen;
>> @@ -2552,16 +2553,23 @@ 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);
>> +
>> + /* move iter to point to the start of mac header */
>> + if (ret == 0)
>> + iov_iter_advance(&msg->msg_iter, vnet_hdr_sz - sizeof(struct virtio_net_hdr));
>> + return ret;
> Let's make the error path the exception
>
> if (ret)
> return ret;
>
> And maybe avoid calling iov_iter_advance if vnet_hdr_sz == sizeof(*vnet_hdr)
>
>> case PACKET_VNET_HDR:
>> + case PACKET_VNET_HDR_SZ:
>> {
>> int val;
>> + int hdr_len = 0;
>>
>> if (sock->type != SOCK_RAW)
>> return -EINVAL;
>> @@ -3931,11 +3945,23 @@ static void packet_flush_mclist(struct sock *sk)
>> if (copy_from_sockptr(&val, optval, sizeof(val)))
>> return -EFAULT;
>>
>> + if (optname == PACKET_VNET_HDR_SZ) {
>> + if (val != sizeof(struct virtio_net_hdr) &&
>> + val != sizeof(struct virtio_net_hdr_mrg_rxbuf))
>> + return -EINVAL;
>> + hdr_len = val;
>> + }
>> +
> } else {
> hdr_len = sizeof(struct virtio_net_hdr);
> }
>
>> lock_sock(sk);
>> if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {
>> ret = -EBUSY;
>> } else {
>> - po->has_vnet_hdr = !!val;
>> + if (optname == PACKET_VNET_HDR) {
>> + po->has_vnet_hdr = !!val;
>> + if (po->has_vnet_hdr)
>> + hdr_len = sizeof(struct virtio_net_hdr);
>> + }
>> + po->vnet_hdr_sz = hdr_len;
> then this is not needed
>> ret = 0;
>> }
>> release_sock(sk);
>> @@ -4070,6 +4096,9 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
>> case PACKET_VNET_HDR:
>> val = po->has_vnet_hdr;
>> break;
>> + case PACKET_VNET_HDR_SZ:
>> + val = po->vnet_hdr_sz;
>> + break;
>> case PACKET_VERSION:
>> val = po->tp_version;
>> break;
>> diff --git a/net/packet/internal.h b/net/packet/internal.h
>> index 48af35b..e27b47d 100644
>> --- a/net/packet/internal.h
>> +++ b/net/packet/internal.h
>> @@ -121,7 +121,8 @@ struct packet_sock {
>> origdev:1,
>> has_vnet_hdr:1,
>> tp_loss:1,
>> - tp_tx_has_off:1;
>> + tp_tx_has_off:1,
>> + vnet_hdr_sz:8; /* vnet header size should use */
> has_vnet_hdr is no longer needed when adding vnet_hdr_sz. removing that simplifies the code
So we are going to indicate whether the packet socket has a vnet header
based on vnet_hdr_sz it is set to, right?
>
> drop the comment. That is quite self explanatory from the variable name.
>
>> int pressure;
>> int ifindex; /* bound device */
>> __be16 num;
>> --
>> 1.8.3.1
>>
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