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Date: Sun, 12 Feb 2023 04:54:37 -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 2/2] net/packet: send and receive pkt with given
vnet_hdr_sz
On Fri, Feb 10, 2023 at 10:36:16AM -0500, Willem de Bruijn wrote:
> Michael S. Tsirkin wrote:
> > On Fri, Feb 10, 2023 at 12:01:03PM +0800, 沈安琪(凛玥) wrote:
> > >
> > > 在 2023/2/9 下午9:07, Michael S. Tsirkin 写道:
> > > > On Thu, Feb 09, 2023 at 08:43:15PM +0800, 沈安琪(凛玥) wrote:
> > > > > From: "Jianfeng Tan" <henry.tjf@...group.com>
> > > > >
> > > > > When raw socket is used as the backend for kernel vhost, currently it
> > > > > will regard the virtio net header as 10-byte, which is not always the
> > > > > case since some virtio features need virtio net header other than
> > > > > 10-byte, such as mrg_rxbuf and VERSION_1 that both need 12-byte virtio
> > > > > net header.
> > > > >
> > > > > Instead of hardcoding virtio net header length to 10 bytes, tpacket_snd,
> > > > > tpacket_rcv, packet_snd and packet_recvmsg now get the virtio net header
> > > > > size that is recorded in packet_sock to indicate the exact virtio net
> > > > > header size that virtio user actually prepares in the packets. By doing
> > > > > so, it can fix the issue of incorrect mac header parsing when these
> > > > > virtio features that need virtio net header other than 10-byte are
> > > > > enable.
> > > > >
> > > > > 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>
> > > > Does it handle VERSION_1 though? That one is also LE.
> > > > Would it be better to pass a features bitmap instead?
> > >
> > >
> > > Thanks for quick reply!
> > >
> > > I am a little confused abot what "LE" presents here?
> >
> > LE == little_endian.
> > Little endian format.
> >
> > > For passing a features bitmap to af_packet here, our consideration is
> > > whether it will be too complicated for af_packet to understand the virtio
> > > features bitmap in order to get the vnet header size. For now, all the
> > > virtio features stuff is handled by vhost worker and af_packet actually does
> > > not need to know much about virtio features. Would it be better if we keep
> > > the virtio feature stuff in user-level and let user-level tell af_packet how
> > > much space it should reserve?
> >
> > Presumably, we'd add an API in include/linux/virtio_net.h ?
>
> If packet sockets do not act on the contents of these extended fields,
> it's probably better to leave them opaque.
Well. If the point is to support VERSION_1 which the
commit log says it is, the switch to LE format then does affect
all fields, both used and unused by the packet socket.
> This patch series probably should be one patch. The new option in the
> first patch modifies the data path. Now there is one SHA1 at which its
> behavior would not work.
>
> >
> > > >
> > > >
> > > > > ---
> > > > > net/packet/af_packet.c | 48 +++++++++++++++++++++++++++++++++---------------
> > > > > 1 file changed, 33 insertions(+), 15 deletions(-)
> > > > >
> > > > > diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
> > > > > index ab37baf..4f49939 100644
> > > > > --- a/net/packet/af_packet.c
> > > > > +++ b/net/packet/af_packet.c
> > > > > @@ -2092,18 +2092,25 @@ 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;
> > > > > + int ret;
> > > > > - 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))
> > > > > return -EINVAL;
> > > > > - return memcpy_to_msg(msg, (void *)&vnet_hdr, sizeof(vnet_hdr));
> > > > > + ret = memcpy_to_msg(msg, (void *)&vnet_hdr, sizeof(vnet_hdr));
> > > > > +
> > > > > + /* reserve space for extra info in vnet_hdr if needed */
> > > > > + if (ret == 0)
> > > > > + iov_iter_advance(&msg->msg_iter, vnet_hdr_sz - sizeof(vnet_hdr));
> > > > > +
>
> How about
>
> struct virtio_net_hdr_mrg_rxbuf vnet_hdr { .num_buffers = 0 };
>
> ..
>
> ret = memcpy_to_msg(msg, (void *)&vnet_hdr, vnet_hdr_sz);
>
> To avoid the iov_iter_advance and properly initialize those bytes.
>
> > > > > + return ret;
> > > > > }
> > > > > /*
> > > > > @@ -2311,7 +2318,7 @@ 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 +2559,23 @@ 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;
> > > > > }
> > > > > static int tpacket_fill_skb(struct packet_sock *po, struct sk_buff *skb,
> > > > > @@ -2730,6 +2744,7 @@ 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;
> > > > > mutex_lock(&po->pg_vec_lock);
> > > > > @@ -2811,8 +2826,9 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
> > > > > tlen = dev->needed_tailroom;
> > > > > if (po->has_vnet_hdr) {
> > > > > vnet_hdr = data;
> > > > > - data += sizeof(*vnet_hdr);
> > > > > - tp_len -= sizeof(*vnet_hdr);
> > > > > + vnet_hdr_sz = po->vnet_hdr_sz;
> > > > > + data += vnet_hdr_sz;
> > > > > + tp_len -= vnet_hdr_sz;
> > > > > if (tp_len < 0 ||
> > > > > __packet_snd_vnet_parse(vnet_hdr, tp_len)) {
> > > > > tp_len = -EINVAL;
> > > > > @@ -2947,6 +2963,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> > > > > int offset = 0;
> > > > > struct packet_sock *po = pkt_sk(sk);
> > > > > bool has_vnet_hdr = false;
> > > > > + int vnet_hdr_sz;
> > > > > int hlen, tlen, linear;
> > > > > int extra_len = 0;
> > > > > @@ -2991,7 +3008,8 @@ 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);
> > > > > + vnet_hdr_sz = po->vnet_hdr_sz;
> > > > > + err = packet_snd_vnet_parse(msg, &len, &vnet_hdr, vnet_hdr_sz);
> > > > > if (err)
> > > > > goto out_unlock;
> > > > > has_vnet_hdr = true;
> > > > > @@ -3068,7 +3086,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
> > > > > 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);
> > > > > }
> > > > > @@ -3452,10 +3470,10 @@ 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);
> > > > > + vnet_hdr_len = pkt_sk(sk)->vnet_hdr_sz;
> > > > > + 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
> > > > > --
> > > > > 1.8.3.1
> >
>
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