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Date: Mon, 27 Feb 2023 23:31:53 -0500
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: 沈安琪(凛玥) <amy.saq@...group.com>,
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
沈安琪(凛玥) wrote:
>
> 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.
That is certainly fine. If patches are not expected to be merged,
perhaps label them RFC to avoid confusion.
>
>
> >
> >> @@ -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?
That's the idea. That has all state. The boolean doesn't add any useful info.
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