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Date: Mon, 27 Feb 2023 12:46:58 -0500
From: "Michael S. Tsirkin" <mst@...hat.com>
To: Willem de Bruijn <willemdebruijn.kernel@...il.com>
Cc: 沈安琪(凛玥) <amy.saq@...group.com>,
netdev@...r.kernel.org, davem@...emloft.net, jasowang@...hat.com,
谈鉴锋 <henry.tjf@...group.com>
Subject: Re: [PATCH v2] net/packet: support mergeable feautre of virtio
typo in $subj
On Mon, Feb 27, 2023 at 11:31:51AM -0500, Willem de Bruijn wrote:
> 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
worthy of
> > that larger than one-mbuf size will be dropped in vhost worker's
are larger
> > 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
you mean with this feature enabled in guest but without support in tap
> > 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.
as well as what?
> > This incorrect mac header parsing will cause packet be dropped due to
to be dropped
> > 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
currently used
> > 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
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>
>
> net-next is closed
> > @@ -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
>
> drop the comment. That is quite self explanatory from the variable name.
besides, it's agrammatical :)
> > int pressure;
> > int ifindex; /* bound device */
> > __be16 num;
> > --
> > 1.8.3.1
> >
>
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