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Message-ID: <f2fa7c95-1884-94aa-49e7-c82f47bf82cd@antgroup.com>
Date: Wed, 29 Mar 2023 20:14:43 +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 v6] net/packet: support mergeable feature of virtio
在 2023/3/29 上午12:30, 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 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>
>> ---
>>
>> V5 -> V6:
>> * rebase patch based on 6.3-rc2
>>
>> include/uapi/linux/if_packet.h | 1 +
>> net/packet/af_packet.c | 88 +++++++++++++++++++++-------------
>> net/packet/diag.c | 2 +-
>> net/packet/internal.h | 2 +-
>> 4 files changed, 59 insertions(+), 34 deletions(-)
>>
>> diff --git a/include/uapi/linux/if_packet.h b/include/uapi/linux/if_packet.h
>> index 78c981d6a9d4..9efc42382fdb 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 497193f73030..b13536767cbe 100644
>> --- a/net/packet/af_packet.c
>> +++ b/net/packet/af_packet.c
>> @@ -2090,18 +2090,18 @@ static unsigned int run_filter(struct sk_buff *skb,
>> }
>>
>> @@ -3925,11 +3938,19 @@ packet_setsockopt(struct socket *sock, int level, int optname, sockptr_t optval,
>> 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;
>> + }
>> +
> Since the below requires a change, I'd prefer
>
> if (optname == PACKET_VNET_HDR_SZ) {
> ...
> } else {
> hdr_len = val ? sizeof(struct virtio_net_hdr) : 0;
> }
>
> Rather than first doing that and then modifying val in the case of
> PACKET_VNET_HDR_SZ.
Good point. We will address this comment in the next version of patch.
>> lock_sock(sk);
>> if (po->rx_ring.pg_vec || po->tx_ring.pg_vec) {
>> ret = -EBUSY;
>> } else {
>> - packet_sock_flag_set(po, PACKET_SOCK_HAS_VNET_HDR, val);
>> + po->vnet_hdr_sz = hdr_len;
> Needs to use WRITE_ONCE to match the READ_ONCE elsewhere
Thanks for pointing out. We will fix this in the next version of patch.
>
>> ret = 0;
>> }
>> release_sock(sk);
>> @@ -4062,7 +4083,10 @@ static int packet_getsockopt(struct socket *sock, int level, int optname,
>> val = packet_sock_flag(po, PACKET_SOCK_ORIGDEV);
>> break;
>> case PACKET_VNET_HDR:
>> - val = packet_sock_flag(po, PACKET_SOCK_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 de4ced5cf3e8..5cf13cf0b862 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 (packet_sock_flag(po, PACKET_SOCK_ORIGDEV))
>> pinfo.pdi_flags |= PDI_ORIGDEV;
>> - if (packet_sock_flag(po, PACKET_SOCK_HAS_VNET_HDR))
>> + if (po->vnet_hdr_sz)
>> pinfo.pdi_flags |= PDI_VNETHDR;
>> if (packet_sock_flag(po, PACKET_SOCK_TP_LOSS))
>> pinfo.pdi_flags |= PDI_LOSS;
>> diff --git a/net/packet/internal.h b/net/packet/internal.h
>> index 27930f69f368..63f4865202c1 100644
>> --- a/net/packet/internal.h
>> +++ b/net/packet/internal.h
>> @@ -118,6 +118,7 @@ struct packet_sock {
>> struct mutex pg_vec_lock;
>> unsigned long flags;
>> int ifindex; /* bound device */
>> + u8 vnet_hdr_sz;
> Did you use pahole to find a spot that is currently padding?
>
> This looks good in principle, an int followed by __be16.
Yes, we have checked this spot with pahole to make sure it is a right
place to add vnet_hdr_sz.
Here's the result:
struct packet_sock {
struct sock sk; /* 0 776 */
/* --- cacheline 12 boundary (768 bytes) was 8 bytes ago --- */
struct packet_fanout * fanout; /* 776 8 */
union tpacket_stats_u stats; /* 784 12 */
/* XXX 4 bytes hole, try to pack */
struct packet_ring_buffer rx_ring; /* 800 200 */
/* --- cacheline 15 boundary (960 bytes) was 40 bytes ago --- */
struct packet_ring_buffer tx_ring; /* 1000 200 */
/* --- cacheline 18 boundary (1152 bytes) was 48 bytes ago --- */
int copy_thresh; /* 1200 4 */
spinlock_t bind_lock; /* 1204 4 */
struct mutex pg_vec_lock; /* 1208 32 */
/* --- cacheline 19 boundary (1216 bytes) was 24 bytes ago --- */
long unsigned int flags; /* 1240 8 */
int ifindex; /* 1248 4 */
u8 vnet_hdr_sz; /* 1252 1 */
/* XXX 1 byte hole, try to pack */
__be16 num; /* 1254 2 */
struct packet_rollover * rollover; /* 1256 8 */
struct packet_mclist * mclist; /* 1264 8 */
atomic_t mapped; /* 1272 4 */
enum tpacket_versions tp_version; /* 1276 4 */
/* --- cacheline 20 boundary (1280 bytes) --- */
unsigned int tp_hdrlen; /* 1280 4 */
unsigned int tp_reserve; /* 1284 4 */
unsigned int tp_tstamp; /* 1288 4 */
/* XXX 4 bytes hole, try to pack */
struct completion skb_completion; /* 1296 32 */
struct net_device * cached_dev; /* 1328 8 */
/* XXX 8 bytes hole, try to pack */
/* --- cacheline 21 boundary (1344 bytes) --- */
struct packet_type prot_hook; /* 1344 72 */
/* XXX 56 bytes hole, try to pack */
/* --- cacheline 23 boundary (1472 bytes) --- */
atomic_t tp_drops; /* 1472 4 */
/* Force padding: */
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
atomic_t :32;
/* size: 1536, cachelines: 24, members: 23 */
/* sum members: 1403, holes: 5, sum holes: 73 */
/* padding: 60 */
};
>> __be16 num;
>> struct packet_rollover *rollover;
>> struct packet_mclist *mclist;
>> @@ -139,7 +140,6 @@ enum packet_sock_flags {
>> PACKET_SOCK_AUXDATA,
>> PACKET_SOCK_TX_HAS_OFF,
>> PACKET_SOCK_TP_LOSS,
>> - PACKET_SOCK_HAS_VNET_HDR,
>> PACKET_SOCK_RUNNING,
>> PACKET_SOCK_PRESSURE,
>> PACKET_SOCK_QDISC_BYPASS,
>> --
>> 2.19.1.6.gb485710b
>>
>>
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